ALBERT

Description: Abstract In this work, cobalt phosphide (CoP) nanoparticles were successfully decorated on an ultrathin g‐C3N4 nanosheet photocatalysts by in situ chemical deposition. The built‐in electric field formed by heterojunction interface of the CoP/g‐C3N4 composite semiconductor can accelerate the transmission and separation of photogenerated charge‐hole pairs and effectively improve the photocatalytic performance. TEM, HRTEM, XPS, and SPV analysis showed that CoP/g‐C3N4 formed a stable heterogeneous interface and effectively enhanced photogenerated electron‐hole separation. UV‐vis DRS analysis showed that the composite had enhanced visible light absorption than pure g‐C3N4 and was a visible light driven photocatalyst. In this process, NaH2PO2 and CoCl2 are used as the source of P and Co, and typical preparation of CoP can be completed within 3 hours. Under visible light irradiation, the optimal H2 evolution rate of 3.0 mol% CoP/g‐C3N4 is about 15.1 μmol h−1. The photocatalytic activity and stability of the CoP/g‐C3N4 materials were evaluated by photocatalytic decomposition of water. The intrinsic relationship between the microstructure of the composite catalyst and the photocatalytic performance was analyzed to reveal the photocatalytic reaction mechanism.

Description: Abstract High volume fraction SiC nanowires‐reinforced SiC composites (SiCNWs/SiC) were prepared by hybrid process of chemical vapor infiltration and polymer impregnation/pyrolysis in this research. SiCNWs networks are first to be made promising a high volume fraction (20 vol%), and the pyrolytic carbon (PyC) interphase with 5 nm is designed on SiCNWs surface to optimize the bonding condition between SiCNWs and SiC matrix. Nanoindentation shows a modulus of 494 ± 14 GPa of SiCNWs/SiC composites without interphase comparing to the one with PyC interphase of 452 ± 13 GPa. However, the 3‐point bending test shows a higher strength of the composite with PyC interphase (273 ± 32 MPa) comparing with the one without interphase (240 ± 38 MPa). The fracture surface is observed under SEM, which shows a longer SiCNWs pullout of the composite with PyC interphase. The energy dissipation during the 3‐point bending test is calculated by the length of nanowire pull‐out, it demonstrates that the SiCNWs with PyC interphase possess better performance for toughening composite. Further characterization proves that the PyC interphase can give SiCNWs/SiC composites higher fracture toughness (4.49 ± 0.44 MPa·m1/2) than the composites without interphase (3.66 ± 0.28 MPa·m1/2).

Description: Here, we report a multicolor PersL phosphor Sr Ga GeO :Pr .The PersL color can be tuned from deep red to blue. It reveals that the multicolor luminescence of the phosphor is essentially associated with the crossrelaxation effect of Pr . What's more,the PersL lifetime of the multicolor phosphor can be also tuned. Based on the unique features of Sr Ga GeO :Pr phosphor, some luminescent images are fabricated for dynamic multicolor anticounterfeiting. Abstract Persistent luminescence (PersL) phosphor is a glow‐in‐the‐dark material that has been widely applied. Here, we report a multicolor PersL phosphor Sr2Ga2GeO7:Pr3+. The PersL color can be tuned from deep red to blue. It reveals that the luminescent color modulation of the Sr2Ga2GeO7:Pr3+ phosphor is essentially associated with the cross‐relaxation effect of Pr3+ in the host with low‐phonon assistance energy. The PersL lifetime of the multicolor phosphors can be also tuned. Based on the unique features of Sr2Ga2GeO7:Pr3+ phosphor, some simple PersL images are fabricated to emit dynamic multicolor information, and it shows that the PersL image even depicts dynamic multicolor anticounterfeiting.

Description: Abstract Although great advance has been made in glass science, predicting luminescence properties of laser glass poses a significant challenge for scientists due to the complex relationship between the composition, structure, and properties of the rare earth ions doped laser glasses. The development of high‐performance laser glass usually relies on intuition and trial‐and‐error. Recently, with the proposal of the materials genome engineering, the “glass genome” has also attracted much attention. Here, the structure of the Nd3+ doped B2O3‐Li2O laser glasses was analyzed using Fourier transform infrared spectra and nuclear magnetic resonance, revealing that the glass contains similar glass‐forming ion‐centered coordination polyhedron structure groups to the neighbor congruent glassy compounds. The structure and properties of glass largely depend on the neighbor congruent glassy compounds. Therefore, the structure and luminescence properties of Nd3+ doped B2O3‐Li2O and B2O3‐MgO‐Li2O laser glasses can be quantitatively predicted via the neighbor congruent glassy compounds. The predictive values are in good agreement with the experimental data, which indicates that our approach is an effective way to predict the structure and luminescence properties of Nd3+ doped borate laser glasses.

Description: Abstract Ba2Ti9O20 single‐phase ceramics were prepared by reaction sintering method using TiO2 and BaCO3 as raw materials after heat treating at 1150°C for 10h. Furthermore, the formation mechanism and microstructure evolution of Ba2Ti9O20 ceramics prepared by reaction sintering method were investigated. The formation behavior of Ba2Ti9O20 phase was analyzed from the perspective of diffusion, where the reaction activation energy required for the process was calculated to be about 386.17kJ/mol. Combined with the scanning electron microscopy and the energy dispersive spectrometer, it was revealed that the pores on Ba2Ti9O20 grains in the process of reaction sintering might be caused by the absence of oxygen element. Meanwhile, the reason for the roughness of ceramic surface was that the local inhomogeneous distribution of barium on the surface of Ba2Ti9O20 grain leaded to the enrichment of titanium.

Description: Abstract Two dimensional (2D) SnS2/MoS2 heterojunction with a 2D/2D novel structure were used as electrodes materials for enhanced supercapacitor performance. Compared with the sole SnS2, the as‐prepared 2D/2D SnS2/MoS2 layered heterojunction has exhibited great improvement in supercapacitor properties. This novel structure can effectively prevent agglomeration and stacking in electrochemical process, and 2D/2D structure is beneficial to intercalation and desorption of ions in electrochemical processes. The experiment result shows that MoSn5 (Samples with 5% Mo:Sn mole ratios) display a specific capacitance of 466.6 F/g at the current Density of 1 A/g in 0.5M Potassium hydroxide solution, an impressive cycling stability with 88.2 % capacitance retention at current density of 4 A/g. In addition, the as‐fabricated symmetric supercapacitor exhibited high energy density of 115 Wh kg‐1 at the power density of 2230 W kg‐1. This work provides a fundamental investigation of 2D/2D layered material synergistic effect on the electrochemical process.

Description: Abstract Freeze casting is an established method for fabricating porous ceramic structures with controlled porosity and pore geometries. Herein, we developed a novel freeze casting and freeze drying process to fabricate tubular anode supports for solid oxide fuel cells (SOFCs). Freeze casting was performed by injecting aqueous anode slurry to a dual‐purpose freeze casting and freeze drying mold wrapped with peripheral coils for flowing a coolant. With the use of an ice barrier layer, proper control of the experimental setup, and adjustments in the drying temperature profile, complete drying of the individual anode tubes was achieved in four hours. The freeze‐cast anode tubes contained radially aligned columnar pore channels, thus significantly enhancing the gaseous diffusion. SOFC single cells with conventional Ni/yttria‐stabilized zirconia (YSZ)/strontium‐doped lanthanum manganite (LSM) materials were prepared by dip coating the thin functional layers onto the anode support. Single‐cell tests showed that the concentration polarization was low owing to the highly porous anode support with directional pores. With H2/N2 (1:1) fuel, maximum power densities of 0.47, 0.36, and 0.27 W/cm2 were recorded at 800, 750, and 700 °C, respectively. Our results demonstrate the feasibility of using freeze casting to obtain tubular SOFCs with desired microstructures and fast turn‐around times. This article is protected by copyright. All rights reserved.

Description: Abstract Defect engineering plays an important role in property modification for piezoelectric materials. In this work, we pay much attention to the effect of Nb non‐stoichiometry on structure and properties of typical 0.95(K0.45Na0.55)Nb1+xO3‐0.05Bi0.5Na0.5HfO3 ceramics. Large piezoelectric constant (d33~425 pC/N and d33*~ 482 pm/V) together with high Curie temperature (TC~315 ºC) have been achieved in the ceramics with excess Nb content (x=0.01). However, the ceramics with deficient Nb element have seriously suppressed cryogenic εr‐T curves and deteriorated electrical properties. Multi‐scale characterizations including phase structure, microstructure, defect structure and domain structure have been adopted to explain the corresponding phenomenon. Defect complex of VNb'''''‐Vo.. caused by deficient Nb induces clamped domain wall motion, leading to blocked polarization vector and poor electrical properties. On the contrary, the enhanced properties for the ceramics with excess Nb are attributed to easier domain switching due to the suppressed vacancies. We believe that defect engineering, for example non‐stoichiometry, can not only modulate electrical properties but also help us to understand some fundamental and critical problems about KNN‐based ceramics. This article is protected by copyright. All rights reserved.

Description: Abstract The paper by Lee et al (J Am Ceram Soc 102:4555‐4561, 2019) reports on semiconductor quantum dots (QDs) obtained in a silicate glass matrix by a novel modification of the solid‐state precipitation technique and characterized by a variety of techniques. Based on their experimental data, we critically discuss their assessment of the QDs obtained as CdSe/Cd1−xZnxSe core/shell structures. By analyzing their results (in particular, Raman scattering data) and comparing them to other data available in literature, we show that the data presented give no evidence for the formation of core/shell structures and conclude that the authors obtained rather homogeneous Cd1−xZnxSe QDs without any noticeable compositional gradient.

Description: Abstract Solid‐oxide fuel cells (SOFCs) have the potential to increase electricity generation efficiency, but traditional SOFCs supported by nickel cermets suffer from reliability challenges due to weaker mechanical strength caused by cracking after redox cycling. To solve this problem, a new ceramic anode material, SrFe0.2Co0.4Mo0.4O3−δ (SFCM) combined with Ce0.9Gd0.1O2 (GDC), was evaluated for conductivity and mechanical strength at SOFC operating conditions and after redox cycling. Fracture toughness of SFCM was determined to be (0.124 ± 0.023) MPa√m at room temperature in air, increasing to (0.286 ± 0.038) MPa√m at 600°C. A mixture of SFCM:GDC showed fracture toughness between the two materials, following SFCM's trend with temperature. The SFCM‐GDC anode supported half‐cell strength increases by 31% from room temperature to 600°C as intrinsic stresses remaining from sintering are relaxed and thermal expansion pushes existing cracks closed. Exposure to reducing gasses decreases strength by 29% compared to ambient, due to oxygen vacancy formation and microstructural flaw changes. It is found that SFCM‐GDC based cells tolerate cycling well because of phase stability but weaken from 34.3 to 22.4 MPa due to uniform growth of critical microstructural flaws.

Description: Abstract Photoluminescence of rare earth ions doped glasses could be enhanced by diverse Ag species such as Ag+ ions, Ag+‐Ag+ pairs, Ag nano‐clusters (NCs) and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ions doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, the Ag+ ions and Ag NCs were selectively prepared in the Sm3+ doped borosilicate glass via the Ag+‐Na+ ion exchange. The influence of AgNO3/NaNO3 ratio in the molten salt on the Ag existing states was investigated. The results demonstrate the isolated Ag+ ions exist in the Sm3+ doped borosilicate glass when the ratio of AgNO3/NaNO3 is 1/1000. The Ag NCs are formed in the Sm3+ doped borosilicate glass when the AgNO3/NaNO3 ratio is 1/10. The influences of Ag+ ions or Ag NCs on the photoluminescence of Sm3+ were systematically investigated. The results show that the photoluminescence of Sm3+ was enhanced by the energy transfer from Ag+ ions or Ag NCs to Sm3+. This article is protected by copyright. All rights reserved.

Description: Journal of the American Ceramic Society, EarlyView.

Description: Abstract The Eu3+ ions doped (1‐x)Na0.5Bi0.5TiO3‐xSrTiO3 (Eu‐NBT‐xSTO) thin films were prepared on Pt/Ti/SiO2/Si substrates. Raman analysis reveals that the phase structure may undergo a phase evolution of rhombohedral → rhombohedral + tetragonal (morphotropic phase boundary) → tetragonal with increasing content of STO. The SEM images show that the uniformity and high density of Eu‐NBT‐xSTO films were increased by adding STO, resulting in a pronounced effect on energy‐storage properties. The ɛ‐T curves confirm that a high phase transition diffuseness of γ= 2.02±0.03 and 1.98±0.03 was achieved in Eu‐NBT‐0.24STO and Eu‐NBT‐0.3STO films, respectively. Further, a large recoverable energy‐storage density of 31.5 J/cm3 with an efficiency of 64% was obtained in Eu‐NBT‐0.3STO film, which also exhibited good thermal stability in the temperature range between ‐60 °C and 80 °C as well as long‐term stability up to 1×108 switching cycles. These results suggest that the Eu‐NBT‐xSTO films may be used in the novel and advanced energy‐storage capacitors. This article is protected by copyright. All rights reserved.

Description: Abstract A unique feature of cordierite is the negative thermal expansion of its c‐axis, while the a‐ and b‐axes show positive thermal expansion behavior. The thermal expansion mechanism of cordierite has been investigated in many theoretical studies, but the effect of Ti or Ge doping has not yet been studied theoretically. Here, we investigate the thermal expansion behavior of Ti‐ and Ge‐doped cordierite by ab initio molecular dynamics (AIMD) simulation. The computational cost of AIMD simulation for cordierite doped with Ti or Ge is challenging due to the many different configurations of crystal models. We overcame this computational difficulty by separating the respective models into groups with identical symmetry, then we performed the MD simulation for each different symmetry crystal model. To understand the mechanism of the negative thermal expansion of the c‐axis, we investigated the changes of all the bond lengths and angles. We found that the negative thermal expansion of the c‐axis is coupled with the increase in the O‐Al‐O angle and the shrinkage of the O‐Si‐O angle at the T1 site in cordierite, which suggests rotation of the six‐membered ring. This studyprovides insight into the mechanism of thermal expansion of cordierite with Ti and Ge doping. Moreover, the approach presented here can be generally applied to investigate the thermal expansion behavior of other ceramic materials within reasonable accuracy and computational cost. This article is protected by copyright. All rights reserved.

Description: Abstract Lateral nanoindentation provides access to the scratch hardness of glass surfaces. The specific sensitivity of the scratching experiment to surface mechanical properties can be enhanced when the local load at the tip apex is reduced. Here, we report on ramp‐load scratch tests on a range of silicate glasses using a sphero‐conical tip shape. Similar as with regular scratching experiments using sharp indenters, such tests create a sequence of micro‐ductile, micro‐cracking, and micro‐abrasive regimes. Detailed investigation of the indenter displacement h and of the lateral force FL as recorded in situ, however, reveals pronounced deviations in comparison to Vickers or Berkovich scratching experiments. Most notably, this includes an abrupt increase in both h and FL at moderate normal load, marking the onset of ductile fracture, and a yield point at the transition from fully elastic deformation to the elastic‐plastic regime at low load. For the range of examined silicate glasses, we find that structural cohesion controls yielding, whereas scratch‐induced fracture and micro‐abrasion are dominated by the volume density of bond energy.

Description: Abstract Heat transfer at the interfacial contact is a dominant factor in the thermal behavior of glass during nonisothermal glass molding process. Recent research is developing reliable numerical approaches to quantify contact heat transfer coefficients. In most previous studies, however, both theoretical and numerical models of thermal contact conductance in glass molding attempted to investigate this factor by either omitting surface topography or simplifying the nature of contact surfaces. In fact, the determination of the contact heat transfer coefficient demands a detailed characterization of the contact interface including the surface topography and the thermo‐mechanical behavior of the contact pair. This paper introduces a numerical approach to quantify the contact heat transfer by means of a microscale simulation at the glass‐mold interface. The simulation successfully incorporates modeling of the thermo‐mechanical behaviors and the three‐dimensional topographies from actual surface measurements of the contact pair. The presented numerical model enables the derivation of contact heat transfer coefficients from various contact pressures and surface finishes. Numerical predictions of these coefficients are validated by transient contact heat transfer experiments using infrared thermography to verify the model. This article is protected by copyright. All rights reserved.

Description: Abstract In the (Bi1‐xCex)VO4 (0 ≤ x ≤ 1) system, we found that the (Bi1‐xCex)VO4 (0 ≤ x ≤ 0.1) belongs to the monoclinic scheelite phase and the (Bi1‐xCex)VO4 (0.7 ≤ x ≤ 1) belongs to the tetragonal zircon phase, while the (Bi1‐xCex)VO4 (0.1 〈 x 〈 0.7) belongs to the mixed phases of both monoclinic scheelite and tetragonal zircon structure. Interestingly, two components with near‐zero temperature coefficient of resonant frequency (TCF) appeared in this system. In our previous work, a near‐zero TCF of ~ +15 ppm/oC was obtained in a (Bi0.75Ce0.25)VO4 ceramic with a permittivity (εr) of ~ 47.9, a Qf (Q = quality factor = 1/dielectric loss; f = resonant frequency) value of ~18,000 GHz (at 7.6 GHz). Furthermore, in the present work, another temperature stable microwave dielectric ceramic was obtained in (Bi0.05Ce0.95)VO4 composition sintered at 950 °C and exhibits good microwave dielectric properties with a εr of ~ 11.9, a Qf of ~ 22,360 GHz (at 10.6 GHz), a near‐zero TCF of ~ +6.6 ppm/oC. The results indicate that this system might be an interesting candidate for microwave device applications. This article is protected by copyright. All rights reserved.

Description: Abstract BiFeO3‐BaTiO3 (BF‐BT) solid solutions are lead‐free candidates for high‐temperature piezoelectric applications. BF‐BT ceramics with compositions near the morphotropic phase boundary (MPB) separating rhombohedral (R) and pseudo‐cubic (PC) phases were fabricated by the conventional high temperature sintering method, and their thermal stability and aging properties were studied in detail. BF‐BT ceramics with rhombohedral (R) phase show much better thermal stability and aging properties than those with pseudo‐cubic (PC) or coexistence of PC and R phases. The thermal degradation and aging rates of BF‐BT ceramics with R phase are on the order of 1% and 1.2% per decade, respectively. X‐ray diffraction results reveal that the domain state of poled rhombohedral BF‐BT ceramics is stable up to its Curie temperature, which is responsible for the high thermal stability. The Rayleigh analysis shows that the low aging rate is attributed to the low domain wall contribution to the overall piezoelectric response. The high thermal stability and low aging rates indicate that the lead‐free BF‐BT ceramics with R phase are potential candidates for sensor and transducer applications over a broad temperature range.

Description: Abstract In this report, a mixed‐metal cation‐based halide perovskite (HP) CsPb1−xTixBr3 quantum dots (QDs) were first embedded in the B–Si–Zn glasses using a traditional approach of melt quenching and heat treating. A battery of test results such as photoluminescence, X‐ray diffraction, and time‐resolved attenuation prove that Ti ions do not destroy the properties of CsPbBr3, and they are successfully doped into CsPbBr3. At the same time, the doping of Ti ions also reduces the toxicity of lead. By altering the ratio of Pb/Ti, we determined the optimum ratio of CsPb0.7Ti0.3Br3 QDs through experimental data. Due to the excellent optical properties and stability of CsPb0.7Ti0.3Br3 QDs glass, it was designed to construct the white‐light emitting diode device with tunable color coordinate, color rendering index, correlated color temperature, and a high luminous efficiency compared with CsPbBr3 QDs glass, which may be a promising candidate for the field of lighting and displays.

Description: Abstract Due to their superior piezo‐responses (strain S〉0.3%), bismuth sodium titanate (BNT)‐based relaxor ferroelectrics have received much attention. Compared to other chemical elements, tantalum (Ta) doping provides superior electro‐strain for these ferroelectrics, while the effect of Ta2O5 as oxide additive has been rarely reported. Herein, lead‐free piezoceramics of Bi0.5(Na0.72K0.22Li0.06)0.5TiO3‐xTa2O5 (BNKLT‐xTa2O5, x=0‐0.015) are synthesized. We study the effects of Ta2O5 addition on the crystal structure, piezoelectric responses, dielectric properties, and ferroelectric properties of BNKLT ceramics. All of the ceramics exhibit a typical perovskite structure, and Ta2O5 diffuses into the BNKLT lattice to form a uniform solid solution. The addition of Ta2O5 can make the grains more regular and uniform, while excess Ta2O5 result in finer grains. The undoped BNKLT ceramics show good ferroelectric and piezoelectric properties (remnant polarization Pr=22.5 μC/cm2 and piezoelectric coefficient d33=250 pC/N); however, the addition of Ta2O5 leads to an clear degradation in d33 and Pr. Meanwhile, the addition of an appropriate Ta2O5 amount leads to an increase in the electro‐strain, and the unipolar strain reaches 0.385% under 60 kV/cm for x=0.003, together with a higher normalized strain (d33*=Smax/Emax) of 633 pm/V (x=0.003). The enhanced strain behaviors can be attributed to the coexistence of the ferroelectric and relaxor states, and an excellent electrostriction coefficient Q33 (Q33=S/P2) value of 0.038 m4C‐2 is obtained under 60 kV/cm for x=0.003. This article is protected by copyright. All rights reserved.

Description: Abstract The primary goal of this study is to characterize the influence of the pore saturated gas media and their physical properties on the elasticity of porous ceramic materials. Resonant ultrasound spectroscopic (RUS) measurements were performed on test specimens of alumina with ~40% porosity, zirconia with ~48% porosity and sintered fully dense zirconia to determine the hydrostatic pressure dependent macroscopic elasticity. Here we report the variation of elasticity of porous and full dense samples over approximately five orders of magnitude (800 ‐ 0.02 psi) in absolute pressure. The time evolution of mechanical equilibrium of the porous materials at low pressure and high temperature conditions will also be discussed. This article is protected by copyright. All rights reserved.

Description: Abstract Calcium‐Silicate‐Hydrates (C‐S‐H) gel, the main binding phase in cementitious materials, has a complex multiscale texture. Despite decades of intensive research, the relation between C‐S‐H's chemical composition and mesoscale texture remains experimentally limited to probe and theoretically elusive to comprehend. While the nanogranular texture explains a wide range of experimental observations, understanding the fundamental processes that control particles' size and shape are still obscure. This paper strives to establish a link between the chemistry of C‐S‐H nanolayers at the molecular level and formation of C‐S‐H globules at the mesoscale via the potential‐of‐mean‐force (PMF) coarse‐graining approach. We propose a new thermo‐mechanical load cycling scheme that effectively packs polydisperse coarse‐grained nanolayers and creates representative C‐S‐H gel structures at various packing densities. We find that the C‐S‐H nanolayers percolate at ~ 0% packing fraction, significantly below the percolation of ideal hard contact oblate particles and rather close to that of overlapping ellipsoids. The agglomeration of C‐S‐H nanolayers leads to the formation of globular clusters with the effective thickness of ~ 5nm, in striking agreement with small angle neutron and X‐ray scattering measurements as well as nanoscale imaging observations. The study of pore structure and local packing distribution in the course of densification shows a transition from a connected pore network to isolated nanoporosity. Furthermore, the calculated mechanical properties are in excellent agreement with statistical nanoindentation experiments, positioning nanolayered morphology as a finer description of C‐S‐H globule models. Such high‐resolution description becomes indispensable when investigating phenomena that involve internal building blocks of globules such as shrinkage and creep. This article is protected by copyright. All rights reserved.

Description: Abstract Calcium silicate hydrate (C–S–H) is the main hydration product of cement and the most important binder that plays a pivotal role in the mechanical properties of concrete. However, one of the major drawbacks of C–S–H is its high brittleness and low flexural strength due to its disordered structure at the nano‐ and micro‐scales. Therefore, this study adopts graphene oxide (GO) to modify the structure of C–S–H, and investigates the effects of synthetic methods on the structure of C–S–H–GO composites. In this study, the highly ordered C–S–H–GO composite is successfully synthesized and exhibits itself the high toughness. Moreover, the formation mechanism of the highly ordered C–S–H–GO composite is explored and discussed, which provides a new insight into the design of high‐toughness cement‐based materials.

Description: The Nowotny phase Mo Si C (x = 0.9‐0.764) was found to be catalytically active in electrochemical water splitting. The electrocatalytic activity of the Mo Si C /C/SiC nanocomposite with respect to the hydrogen evolution reaction was characterized by low overpotentials of 22 and 138 mV vs reversible hydrogen electrode for applying 1 and 10 m A cm of current density, respectively, which exceeds that of most Mo‐based electrocatalysts and shows a high stability (over 90 %) during 35 h. Abstract The ternary Nowotny phase (NP), with a composition Mo3+2xSi3C0.6 (x = 0.9‐0.764), is found to be catalytically active in the field of electrochemical water splitting. The NP embedded in a porous SiC/C nanocomposite matrix is synthesized via a single‐source‐precursor approach which involves the reaction of allylhydridopolycarbosilane with MoO2(acac)2. Thermal treatment of the single‐source‐precursor up to 1400°C in a protective atmosphere results in the in situ formation of nanocrystalline Mo3+2xSi3C0.6 immobilized in a thermally and corrosion‐stable SiC/C matrix. The weight fractions of the observed crystalline phases Mo3+2xSi3C0.6 and SiC amount to ca. 28 (26) and 72 (74) wt%, respectively, when prepared at 1400°C (1350°C). The porosity of the formed nanocomposite is adjusted by the addition of polystyrene (PS) as a pore former to the single‐source‐precursor resulting in a specific surface area up to 206 m2/g. The electrocatalytic activity of the Mo3+2xSi3C0.6/C/SiC nanocomposite with respect to the hydrogen evolution reaction (HER) is characterized by low over potentials of 22 and 138 mV vs reversible hydrogen electrode (RHE) for applying 1 and 10 mA cm−2 of current density, respectively. The analyzed electrocatalytic performance exceeds that of most Mo‐based electrocatalysts and shows high stability (over 90%) during 35 hours.

Description: Abstract Making illumination light sources become comfortable to the human eye is a long‐term effort, which justifies the current research on warm white‐light‐emitting diodes (w‐LEDs). In this work, a novel phosphor for w‐LEDs, namely SrGa12O19: Dy3+(SGO: Dy3+), with a low‐color temperature (CT) was designed and synthesized. The crystal structure, the luminescence properties, the thermoluminescence properties and the stability of SGO: Dy3+ were investigated. We demonstrate outstanding luminescent characteristics and excellent stabilities. The intensity of emission light keep remained when excited by a flickering light source with a chopping speed or off‐time of a few seconds, which indicates that the SGO: Dy3+ phosphor has anti‐flicker properties that will be useful for potential applications, as LEDs driven by alternating current (AC‐LED). The chromaticity coordinates and the correlated color temperature (CCT) of SGO: Dy3+ phosphors with different Dy3+ concentrations are close with an optimal doping at 4.00 mol% Dy3+ for chromaticity coordinate (0.4269, 0.4348) and a lowest CCT of 3361 K. The perfect weatherability of this phosphor was also confirmed since the phosphorescence intensity and the color were stable at high temperature and in a high humidity environment. The performance obtained shows that SGO: Dy3+ is a suitable candidate for illumination sources that are beneficial to human health.

Description: Abstract The exhibited geometry of catalytic substrates can have a significant influence on the chemical activity and efficiency. Controlling their geometry can be challenging using the traditional techniques. In this work, we propose new and novel catalytic substrates with architected and controllable topologies based on the minimal surfaces framework. A novel design approach and an additive manufacturing (AM) technique were proposed to manufacture the catalytic substrates using ceramic materials. After 3D printing, their mechanical and flow properties were investigated experimentally. An elastic‐plastic‐damage coupled model was employed to investigate the underlying deformation mechanism of the investigated substrates. Results showed that the CLP substrate exhibited the highest mechanical properties as well as the least pressure drop among the tested substrates. Also, numerical simulations showed that the strut‐based substrates exhibit stress localization which leads to faster failure, while stress is distributed more homogeneously in the sheet‐based substrates. While the model showed to have a good agreement in the experimental and simulation stress‐strain responses, the damage mechanism was not fully captured by the numerical simulations. This was attributed mainly to the process‐induced defects in the form of microcracks and microvoids that can alter the nature of deformation and damage.

Description: Abstract The degradation of mechanical properties due to sintering is one of the major issues during high temperature service of thermal barrier coating system for advanced gas turbines. In this study, a constitutive model was developed by the variational principle, based on the experimentally observed microstructure features of suspension plasma‐sprayed thermal barrier coatings. The constitutive model was further implemented in finite element analysis software, in order to investigate the effect of vertical cracks. The evolution of microstructure during sintering, coating shrinkage and mechanical degradation were predicted. The numerical predictions of Young's modulus were generally in agreement with experimental results. Furthermore, the effect of vertical cracks on the strain tolerance and sintering resistance were discussed. It was confirmed that the introduction of vertical cracks contributed to the improvement of both properties.

Description: Abstract Hollandite has been studied as a candidate ceramic waste form for the disposal of high‐level radioactive waste due to its inherent leach resistance and ability to immobilize alkaline‐earth metals such as Cs and Ba at defined lattice sites in the crystallographic structure. The chemical and structural complexity of hollandite‐type phases developed for high‐level waste immobilization limits the systematic experimental research that is required to understand phase development due to the large number of potential additives and compositional ranges that must be evaluated. Modeling the equilibrium behavior of the complex hollandite‐forming oxide waste system would aid in the design and processing of hollandite waste forms by predicting their thermodynamic stability. Thus, a BaO–Cs2O–TiO2–Cr2O3–Al2O3–Fe2O3–FeO–Ga2O3 thermodynamic database was developed in this work according to the CALPHAD methodology. The compound energy formalism was used to model solid solution phases such as hollandite while the two‐sublattice partially ionic liquid model characterized the oxide melt. Results of model optimizations are presented and discussed including a 1473 K isothermal BaO–Cs2O–TiO2 pseudo‐ternary diagram that extrapolates phase equilibrium behavior to regions not experimentally explored.

Description: Abstract Suppression of charge recombination by thin amorphous alumina layers on metal oxide semiconductors has demonstrated a vital role in electronic appliances beside its role as an insulator. This study reports effect of amorphous alumina (Al2O3) on the structural, electrical, and optical properties of stannous oxide (SnO2). The samples for the present study are prepared as nanofibers by electrospinning a polymeric solution containing aluminum and stannous precursors and subsequent annealing; six samples with varying concentrations of aluminum and stannous are considered. A crystal‐amorphous SnO2/Al2O3 hybrid system was confirmed by both XRD and XPS analysis. Both BET and Mott‐Schottky analysis showed increase in the surface area and conduction band minimum of the sample with increase in the Al content, however, at the expense of its electrical conductivity. The electron lifetime of the sample increased with increase in the Al content, but the electron transport time increase with decrease in the electrical conductivity of the sample. Both Urbach energy measurement and Stoke's shift showed generation of deeper trap state with increase in the Al content. Investigation on sample photovoltaic performance showed that the loss in electrical conductivity of the sample can be compensated by the improved surface area to a certain extent. Interestingly, a composite nanofiber containing equal molar fraction of aluminum and stannous showed orders of magnitude higher photocurrent despite its similar resistivity as that of pure alumina fibers, which is shown to originate from a Fermi energy gradient at the Al2O3/SnO2 interface.

Description: Abstract Ba0.875Ca0.125Ti0.95Sn0.05O3 (BCT‐Sn) was examined for photocatalytic, piezocatalytic, and piezo‐photocatalytic effects. BCT‐Sn powder was poled through corona poling and it was found that poling induces significant impact on photocatalysis. This material was also able to degrade dye (Methylene blue) using poled powder under ultrasonication (piezocatalysis). There was a remarkable effect in dye degradation which is a clear indication of the importance of piezocatalytic behavior in catalytic reactions. Moreover, the piezo‐photocatalytic effect (piezocatalysis + photocatalysis) was also investigated. Results suggested an enormous scope of ferroelectric materials in the field of catalysis.

Description: Abstract A novel pale‐yellow Ba2ZnGe2O7:Bi3+ phosphor with site‐selected excitation and small thermal quenching was synthesized by conventional solid‐state sintering. The crystal structure and luminescence properties have been investigated in detail for the first time using XRD patterns, photoluminescence spectra, diffuse reflection spectra, decay curves, and temperature‐dependent emission spectra. The results reveal that the excitation spectrum of Ba2ZnGe2O7:Bi3+ phosphor locates in the near‐ultraviolet region of 300‐400 nm, and its emission shows an obvious site‐selective excitation phenomenon since Bi3+ ions occupy two different crystallographic sites in the Ba2ZnGe2O7 host. When excited under 360 nm, the phosphors show a pale‐yellow emission in the range of 400‐700 nm with the maximum peaking at 520 nm, while when excited under 316 nm, the phosphors show a blue emission in the range of 400‐700 nm with the maximum peaking at 480 nm. In addition, the emission of Ba2ZnGe2O7:Bi3+ can also be easily controlled by changing the Bi3+ concentration. The Ba2ZnGe2O7:Bi3+ phosphor has small thermal quenching, and its emission intensity only decreases by 2% at 200°C. The results indicate that this novel pale‐yellow Ba2ZnGe2O7:Bi3+ phosphor could be conducive to the development of white light‐emitting diodes.

Description: Abstract The binding of Na+, K+, and Li+ by magnesium silicate hydrate (M–S–H) was investigated in batch sorption experiments. Sorption isotherms and cation exchange measurements indicated the binding of alkalis in cation exchange sites compensating the negative surface charge of M–S–H. Higher pH values led to further deprotonation of the silanol groups and a higher alkali uptake by M–S–H. No significant incorporation of alkalis in the main silica or magnesium oxide sheets was observed. However, the silica sheets were less polymerized in the presence of higher alkali hydroxide concentrations.

Description: Abstract Large‐strain multilayer actuators (MLAs) were fabricated by tape‐casting 0.91(Na1/2 Bi1/2)TiO3–0.06BaTiO3–0.03AgNbO3 (NBT‐BT–3AN) lead‐free incipient piezoceramics co‐fired with Pt inner electrodes. Microstructures, dielectric properties, unipolar and bipolar strain, as well as fatigue properties of the MLAs were investigated. It was found that the actuator consisting of 15 ceramic layers with individual thicknesses of 114 μm could output a large unipolar strain of 0.3% and a dynamic displacement of 5 μm at 6 kV/mm at room temperature. It exhibited excellent cycling stability and provided a high strain of 0.23% after 107 cycles at 6 kV/mm. Moreover, these MLAs still can deliver a strain of 0.20% at 125°C.

Description: Abstract (0.96‐x)K0.48Na0.52NbO3‐0.04Bi0.5Na0.5ZrO3‐xLaFeO3 ceramics (abbreviated as KNN‐BNZ‐LF1000x) with enhanced piezoelectric performance and temperature stability were prepared by the conventional solid‐state sintering method. It was found that the incorporation of LaFeO3 gradually shifted the O‐T phase boundary toward room temperature, while maintaining the Curie temperature above 300°C. The optimal piezoelectricity was found at x = 0.006, with relatively high piezoelectric constant d33 of 345 pC/N as well as a high level of unipolar strain (0.126% at 3 kV/mm). Benefiting from the diffused phase transition induced by appropriate amount of LaFeO3 content, the KNN‐BNZ‐LF6 sample possessed greatly enhanced the temperature stability of , which varied less than 8% in the temperature range of 20°C‐100°C.

Description: Abstract Degradation of thermal barrier coatings (TBCs) in gas‐turbine engines due to calcium–magnesium–aluminosilicate (CMAS) glassy deposits from various sources has been a persistent issue since many years. In this study, state of the art electron microscopy was correlated with X‐ray refraction techniques to elucidate the intrusion of CMAS into the porous structure of atmospheric plasma sprayed (APS) TBCs and the formation and growth of cracks under thermal cycling in a burner rig. Results indicate that the sparse nature of the infiltration as well as kinetics in the burner rig are majorly influenced by the wetting behavior of the CMAS. Despite the obvious attack of CMAS on grain boundaries, the interaction of yttria‐stabilized zirconia (YSZ) with intruded CMAS has no immediate impact on structure and density of internal surfaces. At a later stage the formation of horizontal cracks is observed in a wider zone of the TBC layer.

Description: An effective and facile dip‐loading approach was adopted to fabricate Au nanoparticle (NPs) @TiO2 nanotube arrays (NTAs) heterostructured films with improved H2 generation rate under visible light. Abstract Au nanoparticle (NPs)@TiO2 nanotube arrays (NTAs) heterostructured films with enhanced H2 generation rate under full spectrum were synthesized, by using a controllable and facile dip‐loading approach. Size of the Au NPs was well‐distributed around 7 nm, and the TiO2 NTAs were found vertically aligned. Due to LSPR effect and Schottky contact, the as‐prepared Au NPs@TiO2 NTAs heterostructured films exhibited improved H2 generation abilities as well as photocatalytic degradation abilities. H2 evolution rate of the obtained samples (effective area: 5.25 cm2) reached 74.56 μmol/h, which was 38 times higher than that of the raw TiO2 NTAs. And the Au NPs@TiO2 NTAs samples also showed an obvious advantage over the raw TiO2 NTAs, in methyl orange degradation under UV illumination. Repetition experiments were further carried out to ensure the dip‐loading method was a reliable fabrication process, and the amount of Au particles attached on TiO2 tube walls could be manipulated by changing the dip‐loading cycle times.

Description: Abstract In this study, TiO2 nanorod arrays (TNR), Ag quantum dots (QDs) sensitized with TNR TiO2/Ag, bismuth oxyhalide (BiOI) nanosheets, and Ag QDs co‐modified with TNR and TiO2/BiOI/Ag (TBA) were prepared by a stepwise process. The morphological, structural, compositional, optical, photocatalytic (PC), and photoelectrochemical (PEC) properties of the samples were investigated. The TBA‐2 sample exhibited the highest photocurrent density (281.8 μA/cm2) and photodegradation efficiency (93.3%), with values 9.7 times and 2.25 times higher than those for TNR, respectively. The improvement in sample performance can be attributed to the formation of a heterojunction between BiOI and TiO2, thereby enhancing the absorption of visible light and improving the charge separation efficiency; Ag QDs limit interfacial electron‐hole pair recombination. The experimental results show that TBA can effectively promote light‐induced carrier transport and visible light absorption, while inhibiting the recombination rate of the electron‐hole pairs, PEC, and PC.

Description: Abstract The drastic reduction in dimensions in thin films, together with the low crystallization temperatures used, normally results in a large reduction in the grain size. It has been reported that relaxor ferroelectric states are stabilized at room temperature for fine‐grained ceramics and films that behave as normal ferroelectrics for large grains. In this work, the effects of the grain size reduction on the relaxor characteristics are analyzed for a composition that is already a canonical relaxor with a nonergodic state at room temperature: (Bi0.5Na0.5)1‐xBaxTiO3 (BNBT). The comparison of the local polar ordering within BNBT grains studied with piezoresponse force microscopy on large‐grained ceramics and fine‐grained thin films shows that the development of stable long‐range ferroelectric order with the application of an electric field is hampered due to the small grain size of the grains. The ergodic character of the high‐temperature phase is thus stabilized at room temperature, following a similar mechanism as the one discussed for other noncanonical relaxors.

Description: Abstract In this work, we have prepared a novel (K0.5Na0.5)0.99‐xPrxYb0.01NbO3 (abbreviated as KNN:xPr3+/0.01Yb3+, x = 0.0006, 0.0008, 0.001, 0.002, 0.003, and 0.004) ceramics, which possess visible UC emissions, photochromic (PC) and optical thermometric properties. Under the excitation of a 980‐nm diode laser, all the samples show the featured emissions of Pr3+ ions and the UC emission intensity is greatly dependent on the Pr3+ doping content. The optimal UC luminescence intensity is obtained at x = 0.001. All the prepared samples show a strong PC reaction, and a large luminescence quenching degree (ΔRt) of 74.94% is found. The optical thermometric properties of both the irradiated and unirradiated KNN:0.001Pr3+/0.01Yb3+ ceramics in the temperature range of 123‐573 K have been investigated via measuring the temperature‐dependent UC emission spectra of green emissions, which originate from the two 3P1 and 3P0 thermally coupled levels. It has been found that the prepared samples have both excellent PC behaviors and temperature‐sensing performances. These results suggest that the KNN:xPr3+/0.01Yb3+ ceramics are promising candidates for the applications in PC reaction and thermometers.

Description: Abstract In this work, we present a general sol‐gel protocol for the synthesis of highly porous monolithic transition metal borides via carbothermal conversion of the organic/inorganic interpenetrating networks (IPNs). The formation of organic/inorganic IPNs is clearly demonstrated by simple oxidation and boiling water treatment. A series of transition metal boride porous monoliths, including CrB2, ZrB2, TiB2, Cr3C2/CrB, and ZrB2/ZrC with porosities ranging from 70% to 85% and pore sizes ranging from 0.5 to 35 μm, have been prepared. In each case, a porous hybrid monolith is obtained by drying the wet gel under ambient pressure. It is believed that the formation of organic/inorganic IPNs strengthens the gel network, so that it can withstand the severe changes during desiccation to give out a monolithic xerogel. Samples are characterized by TG‐DSC, XRD, SEM, EDS, TEM, BET, and MIP, and the ceramic monoliths are shown to be well defined and rather homogeneous.

Description: Abstract Sr2[Ti1−x(Al0.5Nb0.5)x]O4 (x = 0, 0.10, 0.25, 0.30, 0.5) ceramics were synthesized by a standard solid‐state reaction process. Sr2[Ti1−x(Al0.5Nb0.5)x]O4 solid solutions with tetragonal Ruddlesdon‐Popper (R‐P) structure in space group I4/mmm were obtained within x ≤ 0.50, and only minor amount (1‐2 wt%) of Sr3Ti2O7 secondary phase was detected for the compositions x ≥ 0.25. The temperature coefficient of resonant frequency τf of Sr2[Ti1−x(Al0.5Nb0.5)x]O4 ceramics was significantly improved from 132 to 14 ppm/°C correlated with the increase in degree of covalency (%) with increasing x. The dielectric constant ɛr decreased linearly with increasing x, while high Qf value was maintained though it decreased firstly. The variation tendency of Qf value was dependent on the trend of packing fraction combined with the microstructure. Good combination of microwave dielectric properties was achieved for x = 0.50: ɛr = 25.1, Qf = 77 580 GHz, τf = 14 ppm/°C. The present ceramics could be expected as new candidates of ultra‐high Q microwave dielectric materials without noble element such as Ta.

Description: A small addition of TaC into HfC (or vice versa) induces a great improvement in materials properties of (Hf1‐xTax)C. Abstract Bond characteristics, mechanical properties, and high‐temperature thermal conductivity of ultrahigh‐temperature ceramics (UHTCs), hafnium carbide (HfC), tantalum carbide (TaC), and their solid solution composites, were investigated using first‐principles calculations. Mulliken analyses revealed that Ta formed stronger covalent bonds with C than did Hf. Bond overlap analyses indicated that the Hf–C bond possessed mixed covalent and ionic bond characteristics, compared with the more covalent character of the Ta–C bond. Consequently, the overall elastic properties were enhanced with increasing number of Ta–C bonds in the composites. The overall metallicity of the composites also increased with increasing TaC content; thus, the mechanical properties did not improve monotonically. Our results indicate that adding a small amount of TaC to HfC or vice versa to produce a composite would create a new UHTC with greatly improved elastic and mechanical properties as well as high‐temperature thermal conductivity.

Description: Abstract The charge compensation mechanisms that occur when Li+ substitutes a 2+ element in superionic conductor (MgCoNiCuZn)O high‐entropy oxide have been studied using a combination of thermogravimetric analysis and X‐ray photoemission spectroscopy. Depending on the concentration of Li+ in the compound, the charge compensation involves first partial oxidation of Co2+ into Co3+ for low fraction of Li+, and then a combination of both the oxidation of cobalt and the formation of oxygen vacancies for large fraction of Li+.

Description: Abstract HBO2‐II ceramics were prepared by cold sintering with 10wt% dehydrated ethanol as the transient liquid phase. When the processing temperature is 30°C, the relative density of the mechanically robust HBO2‐II ceramics increases from 77.5% to 84.5% with increasing the uniaxial pressure from 200 to 500 MPa. It changes less than 0.2% for higher pressure up to 700 MPa. Under a constant uniaxial pressure of 500 MPa, the relative density further increases to 94.7% for the processing temperature of 120°C. HBO2‐I is observed as the secondary phase when the processing temperature is 150°C. In comparison, the compacts prepared in the absence of ethanol are fragile, and the relative densities are 78.5%‐84.5% for the processing temperatures of 30‐120°C and uniaxial pressure of 500 MPa. It is indicated that ethanol promotes the densification significantly through the dissolution‐precipitation mechanism. The permittivity increases with increasing the processing temperature, while the Qf value decreases. The optimal properties with the relative density of 94.7%, εr = 4.21, Qf = 47 500 GHz, and τf = −70.0 ppm/°C were obtained in the single‐phase HBO2‐II ceramics cold sintered at 120°C under 500 MPa for 10 minutes. The relative density and Qf value are significantly higher than those of the HBO2‐II ceramic prepared by sintering the H3BO3 compact at 180°C for 2 hours (70.3% and 32 700 GHz, respectively). The results indicate that the nonaqueous solvent can also be used as the transient liquid phase for cold sintering, so that more materials that are unstable or insoluble in water can be densified by this method.

Description: Abstract Self‐healing capability in wet oxygen atmospheres is the key issue for long term service of SiC/SiC composites in aero‐engines. Polymer derived SiBCN ceramic (PDC SiBCN) was introduced into SiC fiber reinforced SiC as a self‐healing component to obtain SiC/(SiC‐SiBCN)x composites by a newly developed method, namely chemical vapor infiltration combined with polymer infiltration online pyrolysis (CVI + PIOP) process. The weight loss behavior and three‐point bending performance of the samples under different temperatures (1200, 1300 and 1400°C) and different wet oxygen partial pressures were tested up to 100 hours to demonstrate the oxidation behavior of the samples in wet oxygen environments. According to these tests, the antioxidant capacities of samples prepared from different preforms were compared. It has been found that the 2D plain weave samples with higher density have the best resistance to wet oxygen corrosion while the 2D plain weave samples have the worst resistance to wet oxidation and the antioxidant capacities of 2D satin weave samples is between them.

Description: Abstract Low‐permittivity ZnAl2‐x(Zn0.5Ti0.5)xO4 ceramics were synthesized via conventional solid‐state reaction method. A pure ZnAl2O4 solid‐state solution with an Fd‐3m space group was achieved at x ≤ 0.1. Results showed that partial substitution of [Zn0.5Ti0.5]3+ for Al3+ effectively lowered the sintering temperature of the ZnAl2O4 ceramics and remarkably increased the quality factor (Q × f) values. Optimum microwave dielectric properties (εr = 9.1, Q × f = 115,800 GHz and τf = −78 ppm/°C) were obtained in the sample with x = 0.1 sintered at 1400°C in oxygen atmosphere for 10 h. The temperature used for the sample was approximately 250°C lower than the sintering temperature of conventional ZnAl2O4 ceramics.

Description: Abstract A series of Dy3+/Eu3+ single‐ and co‐doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt‐quenching method. A compact glass structure is obtained by the addition of Dy3+/Eu3+ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy3+/Eu3+ fill in the interspaces of glass network and contribute to the conversion of [BO3] to [BO4]. Dy3+/Eu3+ co‐doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white‐emitting glasses have proved the existence of energy transfer. The average lifetime of Dy3+ decreases from 0.251 to 0.165 ms with the increasing Eu3+ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy3+/Eu3+ co‐doped glass shifts from cyan to white with increasing excitation wavelength. A white‐light emission is obtained when the concentration of Dy3+ and Eu3+ equals to 4% and 2%, respectively. Moreover, the Dy3+/Eu3+ co‐doped calcium borosilicate glass shows high‐thermal stability and it may be applicable for high‐quality white LEDs based on high power near ultraviolet (n‐UV) LED chip in the future.

Description: Abstract Freeze‐casting is a technique used to produce structures with anisotropic porosity in the form of well‐defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La0.66Ca0.26Sr0.07 Mn1.05O3. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze‐casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non‐gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB®.

Description: Abstract Here, we select simple Er3+‐doped tellurite glass as model system to systematically explore the up‐conversion, down‐shifting mechanisms with different excitations (980 nm and 447 nm), respectively. We observe for the first time, to the best of our knowledge, that tunable photo‐luminescence occurs from green to red & NIR region, rather than merely from the long‐accepted green to red region. Direct evidence of selective energy transfer mechanism is expounded in detail, and its potential applications are demonstrated. In addition, we provide evidence that the cross‐relaxation process between dopant ions can enhance photo‐luminescence in Er3+ doped tellurite glasses with high dopant concentrations, whereas the crucial reason for emission decrease is the energy loss long‐distance energy migration. These fundamental insights into the photophysical processes in heavily doped photonic glasses will broaden the applications of rare‐earth‐doped materials ranging from optical communications to medical imaging. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Description: Abstract In this work, the influence of starting particle size and sintering conditions on the microstructures and dielectric properties of BaTiO3‐based ceramics coated with 0.3Bi(Zn1/2Ti1/2)O3‐0.7BaTiO3 were investigated to reveal the core‐shell structure by using high resolution transmission electron microscopy technique coupled with energy‐dispersive spectrometer analysis. The ion‐diffusion behavior plays a critical role in the formation and evolution of the core‐shell structure and, therefore, significantly influences the dielectric properties. When using starting powders containing BaTiO3 particles larger than 100 nm in size and sintering for shorter dwelling times (0.5‐2.0 hours), a core‐shell structure could be formed and retained owing to the limited diffusion behavior, enabling BaTiO3‐based ceramics to meet the X8R specification for multilayer ceramic capacitors applications at high temperatures. However, when using 80 nm BaTiO3 nanopowders and further extending the dwelling time to 6.0 hours, more driving energy was provided to prompt ion diffusion, which led to the compositional inhomogeneity becoming homogenized.

Description: Abstract Ba{[Gax,Tax]Ti(1−2x)}O3 ceramics with x equal to 0, 0.0025, 0.005, 0.01, 0.025, and 0.05 have been prepared by conventional solid‐state reaction. Structural and dielectric characterization have been performed to investigate the effect of dipole‐pair substitution concentration on the macroscopic dielectric properties. Ba{[Gax,Tax]Ti(1−2x)}O3 evolves from a classic ferroelectric to a diffuse phase transition (DPT) as x increases. Ba{[Gax,Tax]Ti(1−2x)}O3 for x ≥ 0.01 possesses diffuseness parameters comparable to Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PMN‐PT) and recently reported (Ba0.97Pr0.03)(Ti0.9425Ce0.05)O3 (BPTC), yet it lacks the frequency and temperature dependence of Tm necessary to be a strictly defined relaxor ferroelectric. Additionally, Ba{[Ga0.05,Ta0.05]Ti0.9}O3 possesses a relative permittivity, ɛr, of 700 ± 16% and dissipation factor less than 0.05 at 10 kHz within the temperature range [−75°C, 120°C]. In comparison to BaTiO3, Ba{[Gax,Tax]Ti(1−2x)}O3 possesses enhanced electrical resistivity at and above room temperature. In situ XRD, including Rietveld refinement, have been performed to determine the lattice parameter, coefficient of thermal expansion, and phase transition temperature (Tc) of each composition within the temperature range [RT, 1000°C], thus linking the dielectric properties with the material's structure. These studies have been corroborated by temperature‐dependent Raman spectroscopy to compare the Tc determined by electrical and structural characterization. The properties of Ba{[Gax,Tax]Ti(1−2x)}O3 are discussed in context with available models that describe donor and acceptor dopants spatially separated in the parent matrix, inter‐relating lattice parameter, Curie temperature, and other material properties.

Description: Abstract Ab initio molecular dynamics simulations are executed to probe the short‐range order and the electrical features of the liquid and amorphous boron subarsenide (B12As2). A drastic volume swelling of ~40% is witnessed for the liquid state, relative to the crystal. The density of the melt is found to be close to that of liquid boron. As the temperature applied is gradually decreased, the volume progressively decreases and a glass‐transition zone at around 1400 K is observed. About 14% volume expansion is perceived for the amorphous phase. Due to the drastic density (volume) difference between the liquid and amorphous forms, their atomic structure is found to be different from each other. In the liquid phase at 2500 K, the mean coordination number (CN) of B and As atoms is 4.4 and 2.5, correspondingly. During the solidification process, both average CNs steadily increase and reach values of 5.5 (B‐atom) and 4.14 (As‐atom) at 300 K. The pentagonal pyramid‐like motifs barely survive at 2500 K but during the quenching process they develop progressively and some of which lead to the formation of B12 clusters. In the amorphous state, the chain‐like and A7‐like As‐As clusters are observed. Nonetheless, the noncrystalline state is proposed to be partially similar to the crystalline structure. The liquid state shows a metallic character while the amorphous form presents a semiconducting nature having an energy band gap much smaller than that of the crystalline phase.

Description: Abstract We have used digital holographic tomography (DHT) to study the refractive index (density) changes occurring under Vickers indentations in silica, soda‐lime, and non‐alkaline aluminoborosilicate glasses. The measurements confirm that the maximum refractive index (density) is not constant but increases with load up to 300 gf. At higher loads (500 gf and 1 kgf), a subsurface (median) crack in soda‐lime glass is observed with no apparent surface trace. The appearance of this crack reduces the maximum refractive index (density) observed. In addition, the vertical cross section of the 3D refractive index (density) map has been successfully obtained using a square fiber sample and lateral observation. These results clearly demonstrate a promising potential of DHT to evaluate the shape and the density distribution of the structurally modified zone in a Vickers‐indented glass.

Description: Abstract Weakly coupled relaxors based on compositions (1‐x) BaTiO3‐xBiMeO3, where Me is a metal ion, have attracted attention as potential candidates for high‐temperature high‐energy density capacitors. However, the necessary Bi content is typically high with x = 0.3‐0.4. In order to reduce problems associated with compatibility for base metal electrodes and due to additional problems due to Bi volatility, it is desirable to lower the Bi content in the overall composition for these materials. Here, we have explored a possible way to reduce BiMeO3 content through additional A‐site substitutions viz. Ca and Sn. The relaxor nature and energy storage properties of Sn‐modified (Ba,Ca)(Ti)O3‐BiScO3 ceramics were determined from their dielectric and ferroelectric behaviors. The material showed attractive properties in terms of a frequency‐independent (200 Hz‐1 MHz) dielectric response from room temperature to 200°C, extremely low loss and high‐energy storage efficiency. The structural phenomena underlying the functional properties of Sn‐modified (Ba,Ca)TiO3‐BiScO3 are characterized from temperature‐dependent X‐ray diffraction and pair distribution function analysis. In broader terms, the study illustrates the potential for tailoring relaxor behavior in Pb‐free ferroelectrics by combining phenomena, such as quantum fluctuations and lone pair stereochemical effect associated with different solid‐solution substitutions.

Description: Steps involved for investigation of the effect of AD processing at the substrate interface using NaCl coating. Abstract Aerosol deposition is a feasible method of fabricating dense ceramic films at room temperature by the impact consolidation of submicron‐sized particles on ceramic, metal, glass, and polymer substrates at a rapid rate. Despite the potential usefulness of the aerosol deposition process, there are issues, such as deposition mechanisms and structure of the film‐substrate interface, that are not well understood. We have used complementary structural and microstructural analysis to capture the state of the substrate surface after the aerosol deposition process. The results reveal that modification of the substrate surface by the ejected submicron‐sized particles is essential for the formation of anchoring layer, thereby, a change in internal residual stress state and surface free energy of the substrate is required to deposit film using AD process. Our analysis also suggests that the adhesion between the metal substrate and ceramic particles is possibly contributed by both physical bonding and mechanical interlocking.

Description: Abstract Silicon carbide fiber reinforced MoSi2 matrix composite (SiCf/MoSi2) is prepared by liquid silicon infiltration at 1450°C. SiC fiber preform is first impregnated with phosphomolybdic acid (PMA) solution in ethyl alcohol. After calcinations, the PMA is converted into MoO3. Following the heating in hydrogen atmosphere, the MoO3 is reduced into metallic Mo, leading to a porous SiCf/Mo. The porous preform is then infiltrated with liquid silicon above silicon melting point to produce SiCf/MoSi2. The microstructure evolution and the underlying mechanism are studied. It is found that MoSi2 is formed by dissolution‐precipitation. Through multiple impregnation‐calcination cycles, a fully dense SiCf/MoSi2 can be obtained with MoSi2 as the continuous matrix phase. The presence of Mo is found to significantly reduce the attack of liquid silicon the silicon carbide fiber reinforcements.

Description: Abstract 8 mol% yttria‐stabilized zirconia (8YSZ) ceramic is an oxide ion conductor at atmospheric pressure but shows the onset of p‐type semiconduction, in addition to the preexisting oxide ion conduction, on application of a dc bias in the range 4‐66 Vcm−1 and at temperatures in the range 150°C‐750°C. The p‐type behavior is attributed to the location and hopping of holes on oxygen. This contrasts with the commonly observed introduction of n‐type conduction under reducing conditions and high fields. The hole conductivity increases with both dc bias and pO2. Its occurrence may contribute to the early stages of flash phenomena in 8YSZ ceramics.

Description: Abstract BiMn3Cr4O12 shows an unusual joint multiferroicity, which facilitates the coexistence of considerable ferroelectric polarization and remarkable magnetoelectric coupling in a single‐phase multiferroic material. Based on first‐principles calculations, we investigate the two different types of ferroelectric phase transitions in the BiMn3Cr4O12 material. Our results show that the first ferroelectric phase transition is driven by soft mode and leads BiMn3Cr4O12 into the Cm space group. The predicted ferroelectric polarization in single crystal is about ~9.8 μC/cm2. With the emergence of spin order on both Mn and Cr sublattices, it is the polar Cm structure that triggers the exchange striction mechanism and therefore results in a large type‐II multiferroicity (~1.1 μC/cm2). In addition, the intrinsic direction of the spin‐driven ferroelectric polarization is always opposite to that of the existing Cm phase structure. Our results imply a feasible strategy in searching/designing novel type‐II multiferroics with large ferroelectric polarization.

Description: The crystal structure of Li5La3Ta2O12 and PL spectrum of Li5La3Ta2O12:Mn4+ phosphor with the chromaticity diagram and picture under UV 365 nm lamp. Abstract Li5La3Ta2O12:Mn4+ (LLTO:Mn4+) phosphors are prepared in air via high‐temperature solid‐state method and investigated for their crystal structures and luminescence properties. LLTO:Mn4+ phosphor under excitation at 314 nm shows deep‐red emission peaking at 714 nm due to the 2E→4A2 transition of Mn4+ ion. The excitation bands in the range 220 ‐ 570 nm are attributed to the Mn4+ ‐ O2‐ charge‐transfer band and the 4A2g→4T1g, 2T2g, and 4T2g transitions of Mn4+, respectively. The optimal Mn4+ ion concentration is ~0.4 mol%. The concentration quenching mechanism in LLTO:Mn4+ phosphor is electric dipole‐dipole interaction. The luminous mechanism and temperature quenching phenomenon are explained by the Tanabe‐Sugano energy level diagram and the configurational coordinate diagram of Mn4+ in the octahedron, respectively. The experimental results indicate that LLTO:Mn4+ phosphor has a potential application prospect as candidate of deep‐red component in light‐emitting diode (LED) lighting.

Description: Abstract The effect of the substitution of Na2O with K2O on the viscosity and structure of molten CaO‐SiO2‐CaF2‐based mold fluxes containing alkali‐oxides at high temperatures has been studied. The CaO/SiO2 mass ratio (C/S) and CaF2 were fixed at 0.8 and 10 mass pct., respectively. The total alkali‐oxide was fixed at 20 mass pct. By systematically substituting the Na2O with K2O, the K2O/(Na2O + K2O) mass ratio was modified between 0.0 and 1.0. Using the rotating spindle method to measure the viscosity at high temperatures, the viscosity was found to increase with higher K2O/(Na2O + K2O). From the slope of the temperature dependence of the viscosity, an apparent activation energy was calculated and increased with higher K2O/(Na2O + K2O), from 96 to 154 kJ/mol, due to the cation size effect on the resistance to shearing. Using Raman spectroscopy of as‐quenched fluxes, the mole fraction of Q3 was found to increase, while the mole fractions of Q2 and Q0 decreased with higher K2O/(Na2O + K2O). The nonbridged oxygen per silicon cation (NBO/Si) decreased from 1.97 to 1.58 with increasing K2O/(Na2O + K2O), suggesting greater complexity of the flux structure with higher K2O/(Na2O + K2O), resulting in a higher viscosity.

Description: Abstract A novel tantalate red‐emitting phosphors NaCa1‐xEuxTiTaO6 (x = 0.02‐0.50) is synthesized via the traditional solid‐state reaction sintering. The photoluminescence properties, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and thermal stability are characterized in detail. Photoluminescence spectra show strong red emission monitored at 614 nm at λex = 395 nm. The spectral properties exhibit excellent color purity and chromaticity coordinate (CIE) characteristics. White light‐emitting diodes (w‐LEDs) device are fabricated by the prepared phosphors and show high quality of color‐rendering index. The investigated results suggest that the Eu3+‐doped NaCaTiTaO6 phosphors can be as potential substitute red phosphors for w‐LEDs.

Description: Abstract Piezoceramics are widely‐used in high‐power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three‐stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high‐power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase. Piezoceramics are widely‐used in high‐power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three‐stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high‐power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase.

Description: Abstract ZnO thin films were deposited via atomic layer deposition (ALD) using H2O and H2O2 as oxidants with substrate temperatures from 100°C to 200°C. The ZnO films deposited using H2O2 (H2O2‐ZnO) showed lower growth rates than those deposited with H2O (H2O‐ZnO) at these temperature range due to the lower vapor pressure of H2O2, which produces fewer OH− functional groups; the H2O2‐ZnO films exhibited higher electrical resistivities than the H2O‐ZnO films. The selection of H2O2 or H2O as oxidants was revealed to be very important for controlling the electrical properties of ALD‐ZnO thin films, as it affected the film crystallinity and number of defects. Compared to H2O‐ZnO, H2O2‐ZnO exhibited poor crystallinity within a growth temperature range of 100‐200°C, while H2O2‐ZnO showed a strong (002) peak intensity. Photoluminescence showed that H2O2‐ZnO had more interstitial oxygen and fewer oxygen vacancies than H2O‐ZnO. Finally, both kinds of ZnO thin films were prepared as transparent resistive oxide layers for CIGS solar cells and were evaluated.

Description: Cu2O particles can be produced along with siloxene formation by simply dispersing layered CaSi2 into CuCl2 + HCl aqueous solution through the comproportionation reaction between Cu and [Cu(OH)4]2‐ ions. Abstract We demonstrate that Cu2O particles can be produced along with siloxene formation by simply dispersing layered CaSi2 into an aqueous solution of CuCl2 and HCl at room temperature. The Cl− ions induce oxidative extraction of Ca from CaSi2 to form siloxene and trigger the reductive deposition of Cu particles. All particles are then gradually oxidized to form Cu2O particles under optimized conditions as follows. A trace amount of residual CaSi2 is dissolved in the solution, which provides OH− ions, and a portion of the formed Cu particles are dissolved as [Cu(OH)4]2− ions. Accordingly, Cu2O particles would be formed through the comproportionation reaction between Cu and [Cu(OH)4]2− ions in the solution. However, under conditions with an excess amount of Cl− ions results in further oxidation of Cu to also form Cu2Cl(OH)3. Thus, CaSi2 acts as an effective reduction and/or oxidation mediator to tune the number of Cl− and OH− ions and control the oxidation state of Cu.

Description: The tunable color was obtained via the substitution of Sr2+, Ca2+, Zn2+ and Mg2+ ions for Ba2+ ions under the same excitation conditions. The emission color can be tuned from deep blue (0.15, 0.12) to cyan (0.16, 0.27) due to the variation of crystal field and distortion of the unit cell by replacing part of the host lattice cation Ba2+ with Sr2+, Ca2+, Zn2+ and Mg2+. The emission bands of BMBO:Ce3+, BZBO:Ce3+, BCBO:Ce3+ and BSBO:Ce3+ can be influenced by two factors: the crystal field splitting and centroid shifts. Abstract In this study, Sr2+, Ca2+, Zn2+, and Mg2+ ions act to tune the emission band to the blue‐cyan region in BaxSryB2O5:Ce3+ (BSBO), BaxCazB2O5:Ce3+ (BCBO), BaxZnuB2O5:Ce3+ (BZBO), and BaxMgvB2O5:Ce3+ (BMBO) phosphors. A red shift occurs with the increase of Sr2+, Ca2+, Zn2+, and Mg2+ concentration, and a blue shift occurs when the concentrations of Sr2+, Ca2+, Zn2+, and Mg2+ exceed the critical value. The emission color can be tuned from deep blue (0.15, 0.12) to cyan (0.16, 0.27) upon 365 nm UV lamp excitation due to the crystal field splitting and centroid shifts. The excitation band shift to long wavelength by introducing ions, so that the synthesized phosphor can be better matched with the n‐UV chip. The emission intensity slowly decreases with the temperature increasing. Therefore, the BMBO:Ce3+, BZBO:Ce3+, BCBO:Ce3+, and BSBO:Ce3+ phosphors with relatively good thermal stability were synthesized, which could have potential applications in the n‐UV white LEDs.

Description: Abstract We investigate the thermoelectric properties of bulk polycrystalline samples of WSe2‐based compounds with partial substitutions in the cationic (W) and the anionic (Se) sublattices in the temperature range from 4.2 to 650 K. The substitution of W for Nb leads to a significant increase in the charge carrier concentration, however, deteriorates the charge carrier mobility. In contrast, the substitution of selenium for sulfur increases the charge carrier mobility, the thermal conductivity, and the Seebeck coefficient but conductivity changes non‐monotonical. We show that the addition of sulfur in anionic sublattice affects the grain sizes in the polycrystalline material. Using substitutions in the anionic and cationic sublattices, we find the optimal ratio of the elements for better thermoelectric efficiency. The W0.98Nb0.02Se1.7S0.3 sample showed the best value of the figure of merit ZT = 0.26 (T = 650 K).

Description: Abstract Although heat‐cured concrete (HCC) has received extensive research interests in recent years, it still suffers from problems including coarsened microstructure, low cement hydration degrees, etc, which limited its application. Some of these problems can be solved by internal curing method resulting in low early strength of HCC and low‐production efficiency. This study addressed this issue by activating the aluminosilicate internal curing agent (lightweight fine aggregate, LWFA) with triisopropanolamine (TIPA). The results indicated that more Al3+ and Fe3+ ions were dissolved from LWFA by TIPA, which assisted the formation of hydrates with cement ions in interfacial transition zone (ITZ), and enhanced the density of ITZ in the early stage. The introduction of TIPA was found to increase the early compressive strength of HCC, by approximately 15.3%, 25.9% and 28.0%, respectively for the cement cured for 1, 3, and 7 days compared with control samples. Moreover, the results of rapid chloride migration and water absorption depth also suggested that coupling the aluminosilicate internal curing agent with TIPA improved the pore structure of HCC.

Description: Abstract Rare earth (RE) ions‐doped luminescent nanocrystals (NCs) with numerous unique advantages have attracted tremendous interest for the wide applications from science to engineering, yet suffering from the shortcoming of thermal quenching coming from surface organic ligands. We propose utilizing a facile acid‐base reaction to remove surface organic ligands introduced choosing carboxylic acids as stabilizing agent and weaken thermal quenching. The results showed that the acid‐base reaction displayed an outstanding cleaning effect. After acid‐treatment, most surface organic ligands were removed, and there was no influence on crystal structure and morphology of as‐prepared β‐NaYF4:Er3+ NCs. Meanwhile, with no surface organic ligands capping, β‐NaYF4:Er3+ NCs preferred brighter emission after thermal treatment, including up‐conversion (UC), near‐infrared (NIR), and mid‐infrared (MIR) emission. When calcined the acid‐treated β‐NaYF4:Er3+ NCs in different atmosphere, such as oxygen and reducing atmosphere (15%H2 + 85%N2), an unexpected enhancement of all emission bands in Er3+ was determined under phase transformation temperature, especially in oxygen atmosphere. Furthermore, all the fluorescence lifetimes of Er3+ also exhibited obvious extension. Our results supposed that the β‐NaYF4:Er3+ NCs have promising applications in safety ink, and the acid‐treatment by diluted hydrochloric acid is a general approach to remove deleterious organic ligands on NC surface further to weaken thermal quenching.

Description: Abstract Multicomponent boron‐containing carbide (ie, Zr‐Ti‐C‐B) composites show good ablation resistance. The present work is the first report to introduce the powder fabrication of Zr‐Ti‐C‐B using a new method for solid‐state diffusion of boron atoms. First, the nonstoichiometric carbide (ie, Zr0.8Ti0.2C0.8) with carbon vacancies was fabricated by free‐pressureless spark plasma sintering. Different boron sources such as B2O3, B, and B4C were used to react with the nonstoichiometric carbide. The Zr0.81Ti0.19C0.86B0.14 can be finally generated through the solid‐state diffusion of boron atoms using the B2O3 boron source at 1300°C followed by carbon thermal reduction using the phenolic resins at 1600°C.

Description: An intense green long‐persistent phosphor LaSrAl3O7:Eu2+, was synthesized. Optical data can be encoded on a flexible film by 405 nm laser and decoded by heating or by 980 nm laser, which opens new opportunities for information security system. Abstract Here, a green emission persistent luminescent phosphor LaSrAl3O7:Eu2+ which is chargeable by UV light, was synthesized by solid‐state reaction method. Elemental mapping and fluorescence microscopy photoluminescence of the sample demonstrated the homogeneous distribution of La, Sr, Al, O, and Eu in the phosphor. Rietveld refinement shows that the as‐prepared sample belongs to the tetragonal crystalline structure with space group of P421m. The Eu2+:5d‐4f broad persistent luminescence with maximum emission peaking at 518 nm can be effectively obtained after irradiating in the UV light. A series of excitation temperature‐dependent thermoluminescence measurements were conducted to gain some insight into the information of traps. Additionally, to verify its feasibility of optical data storage, specific information letters were encoded on the LaSrAl3O7:Eu2+ phosphor films using the laser of 405 nm, then the stored information could indeed be read out by thermal stimulation as expected. Meanwhile, NIR photo‐stimulated red persistent luminescence was also obtained, which holds great potential for optical information storage. Finally, combined with the experimental and density functional theory calculation results, we proposed a tentative schematic diagram to account for the PersL and photo‐stimulated persistent luminescence mechanism in LaSrAl3O7:Eu2+ phosphor.

Description: Abstract The influence of different SPS‐based methods, that is, conventional spark plasma sintering (SPS), flash SPS (FSPS), and reactive SPS (RSPS) on the properties of Al2O3/SiC composite was investigated. It was shown that the application of preliminary high energy ball milling of the powders significantly enhances the sinterability of the ceramics. It was also demonstrated that FSPS provides unique conditions for rapid, that is, less than a minute, consolidation of refractory ceramics. The Al2O3‐20 wt% SiC composite produced by FSPS possesses the highest relative density (~99%), fracture toughness (7.5 MPa m1/2), hardness (20.3 GPa) and wear resistance among all ceramics produced by other SPS‐based approaches with dwelling time 10 minutes. The RSPS ceramics hold the highest Young's modulus (390 GPa). Substitution of micron‐sized Al2O3 particles by nano alumina does not lead to measurable enhancement of the mechanical properties.

Description: Abstract The effect of the structural environment on the Cl− ion conductivity was demonstrated in LaOCl‐based solid electrolytes. By replacing the La3+ site with lower‐valent Mg2+ or Ca2+ ions, the conductivity was enhanced owing to the formation of a Cl− ion vacancy. Despite the same dopant content, the conductivity of La0.8Ca0.2OCl0.8 was considerably greater than La0.8Mg0.2OCl0.8. This enhancement of the conductivity was influenced by the high ionicity of the Cl− ions, which facilitated the weakening of the La‐Cl bond cleavage to conduct inside the lattice. The elongation of the La‐La distance, associated with the Cl− ion conduction, could also cause an increase of the conductivity.

Description: Abstract The diminished conductivity of pristine grain boundaries in oxide‐ion conducting electrolytes, such as (Ce,Gd)O2 and (Zr,Y)O2, is widely interpreted with the Mott–Schottky space‐charge model, or less frequently, with the Gouy–Chapman space‐charge model. Although routinely applied to the entire compositional range of solid solutions, from dilute to concentrated, these models, being based on the Poisson–Boltzmann formalism, are limited in their range of validity to dilute solutions of point defects. Analysing the grain‐boundary properties of concentrated solid solutions with such models is expected to lead to errors and inconsistencies. In this study we employ Poisson–Cahn theory to analyse literature data for the grain‐boundary resistance of CeO2–Gd2O3 materials as a function of Gd concentration. Poisson–Cahn theory combines the Cahn–Hilliard theory of inhomogeneous systems with the Poisson equation of electrostatics and it is valid over the entire compositional range. We treat the realistic case of a restricted equilibrium: Gd accumulation profiles are frozen‐in from sintering temperatures, while the oxygen‐vacancy distributions are in equilibrium at sintering and (much lower) measurement temperatures. Data for the grain‐boundary resistance are also analysed with the standard analytical expressions from the Mott–Schottky and Gouy–Chapman models. Outside the domain of their validity, these expressions are found to perform poorly. In general, we emphasise the importance of treating the interfacial properties of concentrated solid solutions with physically appropriate theories. This article is protected by copyright. All rights reserved.

Description: Abstract In the diffusion couple of Ti3SiC2 and Ti3AlC2, only interdiffusion of Si and Al occurred during diffusion treatment process. Based on the concentration profiles of Si and Al measured by electron probe microanalysis (EPMA), the interdiffusion coefficients of Si and Al at 1373‐1673 K in Ti3SiC2–Ti3AlC2 diffusion couple were determined by both the Boltzmann‐Matano (B‐M) method and the Saucer‐Freise (S‐F) method. At the position of Matano plane with the composition of Ti3Al0.5Si0.5C2, the interdiffusion coefficient could be expressed as Dint (m2/s) = 5.6 × 10−4⋅exp [−246 ± 14 (kJ/mol)/RT]. Based on the two methods, the calculated interdiffusion coefficients increased with increasing temperature, and the magnitudes of their absolute values were on the order of 10–13‐10–11 m2/s at 1373‐1673 K. At 1373‐1573 K, the calculated interdiffusion coefficients decreased monotonously with the increase of Si concentration, that is, xSi/(xAl + xSi). But at 1673 K, the variation trend of interdiffusion coefficients with xSi/(xAl + xSi) was no longer monotonous, probably due to the presence of Ti5Si3 phase and voids on Ti3AlC2 side.

Description: Dual tunable visible (380~750 nm) and near‐infrared (1000~1600 nm) emissions have been achieved by selecting the proper excitation scheme—350 nm UV light or 808 nm LD in Bi‐doped germanium‐borate glasses. Abstract The design of functional materials with tunable broadband luminescence performance is still of great interest in the fields of lighting, solar cells, tunable lasers, and optical amplifiers. Here, via a melt‐quenching method, a series of bismuth (Bi)‐doped germanium‐borate glasses with composition of 40GeO2–25B2O3–25Gd2O3–10La2O3–xBi2O3 have been prepared, in which multiple Bi active centers can be stabilized simultaneously. Dual‐modulating modes of visible (380‐750 nm) and near‐infrared (NIR) (1000‐1600 nm) broadband photoemissions were effectively controlled under flexible excitation scheme. Photoluminescence (PL) spectra at low temperature 10‐298 K were appropriately employed to interpret such an unusual wide visible emission band. To further illustrate the origin of NIR component, transmission electron microscopy (TEM) measurement was carried out. It is demonstrated experimentally that the visible emission mainly originates from the collective contribution of the 3P1/3P01S0 transitions of Bi3+, while the broadband NIR luminescence should be related to the formation of low valent Bi+ and (or) Bi0 centers. This work may help to enhance the knowledge of the complex luminescence mechanism for the Bi species and it also enables such transparent glass materials to be a promising candidate for the multifunctional tunable light source.

Description: Abstract This study investigates the influence of reactive MgO (r‐MgO) replacement levels and water‐to‐binder (w/b) ratios on the compressive strength, carbonation front, and pore structure of mortars with r‐MgO and Portland cement (r‐MgO‐PC) as binder. The experimental results reveal that an increase in the w/b ratio decreases the carbonation degree for mortars with 20% r‐MgO, but increases the carbonation degree for mortars with 60% r‐MgO. The r‐MgO replacement level together with the w/b ratio and carbonation degree impacts the type and quantity of the carbonation products, namely Mg‐calcite, nesquehonite and the hydrated amorphous Mg carbonate, which affects the pore structure and compressive strength of the matrix. The maximum strength for mortars with 20% r‐MgO occurs at the lowest w/b ratio (0.45), while the maximum strength for mortars with 60% r‐MgO occurs at the intermediate w/b ratio (0.65). A design of r‐MgO replacement level, w/b ratio in conjunction with the drying and carbonation curing regimes is needed for further advancement and application r‐MgO‐PC system.

Description: Abstract A series of YNbO4: Sm3+ powder phosphors with different doping concentrations were synthesized by a traditional high temperature solid‐state reaction method. The crystal structure of the obtained samples was characterized by means of X‐ray diffraction. Concentration quenching, energy transfer mechanism and luminescence thermal stability of YNbO4: Sm3+ samples were studied through the fluorescence spectra and decays. It was concluded that electric dipole‐dipole interaction was the dominant energy transfer mechanism between Sm3+ ions according to both Van Uitert's model and Dexter's model. By using the Arrhenius model, crossover process was proven to be responsible for the luminescence thermal quenching of Sm3+. Moreover, a novel approach for evaluating the optical transition properties of Sm3+ ion in YNbO4 powders by using the diffuse‐diffraction spectrum and fluorescence decay was examined in the framework of Judd‐Ofelt (J‐O) theory. It was confirmed that the J‐O parameters Ωλ (λ = 2, 4, 6) of Sm3+ in YNbO4 powder were reliable by comparing the radiation transition rate with the measured emission results. This article is protected by copyright. All rights reserved.

Description: a) When mCMAS/mYSZ ≤0.2, the melt reacts with YSZ fellow a grain boundary attack mechanism and a c‐ZrO2 phase is generated by the diffusion of Ca into the YSZ grains; b) When CMAS increases to a certain concentration, a dissolution‐precipitation reaction occurs instead, in which the original YSZ grains can reprecipitate as Y‐lean m‐ZrO2 after being dissolved by the molten CMAS. Abstract Recently, nanostructured thermal barrier coatings have received considerable attention because of some superior properties in comparison with their conventional counterpart. In this study, nanostructured 8 wt% yttria‐stabilized zirconia (n‐YSZ) coatings were deposited by atmospheric plasma spraying, and the degradation behavior caused by molten calcium‐magnesium‐aluminon‐silicate (CMAS) attack was investigated. Results showed that the thermo‐chemical reaction product between CMAS and YSZ (both powders and coatings) is different with the change of CMAS content. At low CMAS concentration, a cubic phase is generated by the diffusion of Ca into YSZ grains. As compared to the conventional YSZ, less C‐ZrO2 is detected for n‐YSZ. When CMAS reaches a certain concentration (eg 15 mg/cm2), disruptive phase transformation from tetragonal to monoclinic will occur and the reaction is more readily for n‐YSZ. Two different chemical reaction mechanisms governing the CMAS content effect were proposed. It should be noted that the nanozone in the coatings plays an important role in the CMAS degradation process, which enhances CMAS infiltration rate and accelerates the chemical reaction, leading to a poor CMAS resistance of the nanostructured coating than that of the conventional counterpart.

Description: Introducing Ca into B site of BaNbO2N helps to suppress Nb4+ species and increase surface hydrophilicity, which contributes to improved photocatalytic activity. Abstract Although BaNbO2N has visible light absorption as far as 740 nm, its photocatalytic activity is generally very poor under ordinary conditions, being incommensurate to its light absorption properties. In this work, we introduce Ca into the B site of BaNbO2N to form a complex perovskite BaNb1−x/3Cax/3O2+yN1−y (0 ≤ x, y ≤ 1). The presence of Ca in BaNbO2N has great impact on a number of important properties such as band gap value, nitrogen content, surface hydrophilicity, and defects levels. In particular, defects such as Nb4+ species are effectively suppressed in Ca‐modified BaNbO2N. More importantly, photocatalytic activity of BaNbO2N for water oxidation reactions is substantially improved after Ca modifications. Compared with pristine BaNbO2N, more than twofold enhancement in photocatalytic oxygen evolution is observed for BaNb0.8Ca0.2O2+yN1−y (x = 0.6). Such improvements probably stem from the suppression of Nb4+ species in the structure as well as enhanced surface hydrophilicity after Ca modification. The facile approach by incorporating alkaline earth cations into crystal structure can be well extended to other perovskite oxynitrides whose photocatalytic activity is subject to those defective species.

Description: Salt flux dissolution method for converting BaZrO3 micrometer to uniform submicron‐powder Abstract The “top‐down” process via direct conversion of the micro (μm)‐to‐submicroscale (sub‐μm) particle was applied in this work by using eutectic chloride salts to prepare BaZrO3. The particle size at optimum condition could be decreased by more than 10 times from 2.1 ± 0.9 μm to 168 ± 23 nm without destroying the 1:1 of Ba:Zr stoichiometry. The uniform sub‐μm‐BaZrO3 powder was sintered in order to obtain ~98% dense ceramic at 1400°C/10 h, which is significantly lower than the 1650°C in normal cases. The microwave dielectric constant, tan δ, and quality factor were also determined. Furthermore, this method also was applied to lead‐free piezoelectric material in the 0.87BaTiO3–0.13BaZrO3–CaTiO3 (0.87BT–0.13BZ–CT) system. The particle size of 0.87BT–0.13BZ–CT was reduced greatly from 〉10 µm to 2.8 ± 0.4 µm. It can be proved that salt flux dissolution method enables high‐purity with uniform sub‐micro/nanometer powder production in one step by using simple laboratory equipment and low‐cost raw materials.

Description: Abstract Due to the high growth rate and environmental‐friendly, fluorine‐free metal‐organic decomposition routes (FF‐MOD) have attracted more attention for growth of high‐quality YBa2Cu3O7‐δ (YBCO) films. Few works have been performed when using technical substrates. In this study, correlation among the sintering process, microstructure, and superconductivity of the YBCO was systematically established on the technical substrates capped with CeO2 layer. We found that the optimal process conditions are mainly related to the enhanced transient liquid phase and BaCeO3. Combined X‐ray diffraction and scanning electron microscopy analyses indicate that high‐quality growth of YBCO film is a trade‐off of two different competition phenomena during sintering: (a) the presence of enhanced transient liquid phase, (b) the formation of BaCeO3 at the interface. The former is beneficial to YBCO epitaxial growth/structure rearrangement, while the latter should be suppressed in view of minimizing YBCO partial decomposition triggered by the interfacial reaction. Moreover, we confirmed that both two aforementioned phenomena are somehow associated with the cross‐linkage between the sintering temperature and pO2 during the YBCO conversion. According to this systemic study, the key parameters are defined to avoid the BaCeO3 formation prior to the YBCO orientation nucleation. Structure and superconductivity of the YBCO film were also investigated. Remarkably, a high Jc value of 3.69 mA/cm2 (77 K, sf) was obtained in the YBCO film grown on the CeO2 technical substrate deposited under optimized deposition conditions, which is rather comparable with that on the LaAlO3 single crystal. TEM cross‐sectional observation reveals that the enhanced Jc (B) properties of the YBCO film are mainly contributed by high density of short stacking faults. This work demonstrates the feasibility of FF‐MOD to fabricate high‐performance YBCO films on the CeO2‐buffered technical substrate.

Description: Abstract The 0.34BiFeO3‐0.46PbTiO3‐0.2BaZrO3 (BF‐PT‐0.2BZ) ternary solid solutions were prepared by the solid‐state reaction methods. Different amounts of Li2CO3‐Bi2O3 (LB) additives were introduced into the based materials after the calcination process. Upon using LB additives, the sintering temperature of BF‐PT‐0.2BZ ceramics was lowered to 950°C, while the relative density was enhanced to the highest of about 97% for LB of 1 wt%. XRD results indicate that BF‐PT‐0.2BZ ceramics exhibit the perovskite structure without detectable second phases. SEM images reveal that BF‐PT‐0.2BZ ceramics are well densified and the grain size is enhanced with the addition of LB. Moreover, the piezoelectric properties are enhanced significantly, achieving the highest d33 and bipolar strain of 350 pC/N and 0.53%, respectively, for BF‐PT‐0.2BZ ceramics with LB of 1 wt%. Our results indicate that low‐temperature sintered BF‐PT‐0.2BZ ceramics with excellent piezoelectric properties have promising applications in multilayer piezoelectric actuators.

Description: Abstract (Al2OC)1−x(AlN)x solid solution‐reinforced Si–Al2O3 composite was successfully synthesized by designed heating of the Al–Si–Al2O3 composite to 580°C and held for 8 hours, followed by heating to 1300°C at a rate of 12°C/h in flowing nitrogen. The reaction mechanism is as follows: after the Al–Si–Al2O3 composite is heated to 580°C and held for 8 hours, an AlN cladding is formed on the surface of the Al powder, thus the composite is preconverted into (Al–AlN cladding structure)–Si–Al2O3 system. With increasing temperature, the AlN cladding ruptures and the reactive Al(l) flows out. The Al(l) preferentially undergoes active oxidation to form metastable Al2O(g), which lowers PO2 inside the composite and inhibits the active oxidation of Si. Moreover, ultrafine carbon is produced by the pyrolysis of the phenolic resin binder. Both metastable Al2O(g) and ultrafine carbon are highly reactive. Therefore, under the induction of AlN and N2, (Al2OC)1−x(AlN)x solid solution is formed by the reaction which easily occurs at a relatively low temperature. In the presence of a large amount of Al2O(g), the PO2 in the composite does not satisfy the condition required for both Si nitridation and active oxidation, so the free Si remains stable in the composite, forming a metal‐non‐oxide‐oxide composite. The cold crushing strength of the composites is up to 305 MPa, and the composites do not show hydration after 20 months of storage in the environment.

Description: Abstract Due to the widely tunable band gap and broadband excitation, CdS quantum dots (QDs) show great promise for yellow‐light luminescence center in white‐light‐emitting devices. The light intensity of the CdS QD‐doped glass was enhanced by doping the Tm3+ ions due to the higher absorption rate. The influence of Tm3+ ions on the surface structure of CdS QDs was enormous according to the first‐principles calculations. Doping Tm3+ ions change the surface state of CdS QDs, which will fix the QDs emission peaks and enhance the luminescence of CdS QDs at a lower heat‐treatment temperature. White‐light emission was obtained by tuning the relative concentration between Tm3+/CdS QDs. However, there is a fundamental challenge to fabricate QD‐doped glass fibers by rod‐in‐tube method since uncontrollable QDs crystallization is hard to avoid. Herein, a white‐light‐emitting borosilicate glass fiber was fabricated by the “melt‐in‐tube” method using a special designed Tm3+/CdS QDs co‐doped borosilicate glass with low‐melting temperature as fiber core. After heat treatment, ideal white‐light emission was observed from the fiber under excitation at single wavelength (359 nm). This finding indicates that Tm3+/CdS QDs co‐doped glass fiber with white‐light‐emitting devices has potential application as gain medium of white‐light‐emitting sources and fiber lasers.

Description: Cover Photograph: Button type specimen of a thermal barrier coating (TBC) for gas turbine application under test in a burner rig environment. Precursors of calcium‐magnesium‐aluminosilicates (CMAS) are injected to the flame to form corrosive deposits. The orange coloring indicates atomic emission spectra of dissolved CMAS constituents. Image Credit: Ms. Hiltrud Moitroux (Forschungszentrum Jülich GmbH). DOI: 10.1111/jace.16465 Cover Photograph: Button type specimen of a thermal barrier coating (TBC) for gas turbine application under test in a burner rig environment. Precursors of calcium‐magnesium‐aluminosilicates (CMAS) are injected to the flame to form corrosive deposits. The orange coloring indicates atomic emission spectra of dissolved CMAS constituents. Image Credit: Ms. Hiltrud Moitroux (Forschungszentrum Jülich GmbH). DOI: 10.1111/jace.16465

Description: Abstract ZrC–SiC ceramics were fabricated by high‐energy ball milling and reactive hot pressing of ZrH2, carbon black, and varying amounts of SiC. The ceramics were composed of nominally pure ZrC containing 0 to 30 vol% SiC particles. The relative density increased as SiC content increased, from 96.8% for nominally pure ZrC to 99.3% for ZrC‐30 vol% SiC. As SiC content increased from 0 to 30 vol%, Young's modulus increased from 404 ± 11 to 420 ± 9 GPa and Vickers hardness increased from 18.5 ± 0.7 to 23.0 ± 0.5 GPa due to a combination of the higher relative density of ceramics with higher SiC content and the higher Young's modulus and hardness of SiC compared to ZrC. Flexure strength was 308 ± 11 MPa for pure ZrC, but increased to 576 ± 49 MPa for a SiC content of 30 vol%. Fracture toughness was 2.3 ± 0.2 MPa·m1/2 for pure ZrC and increased to about 3.0 ± 0.1 MPa·m1/2 for compositions containing SiC additions. The combination of high‐energy ball milling and reactive hot pressing was able to produce ZrC–SiC ceramics with sub‐micron grain sizes and high relative densities with higher strengths than previously reported for similar materials.

Description: Journal of the American Ceramic Society, Volume 102, Issue 10, Page 5701-5704, October 2019.

Description: Abstract Correlating the melting rates of feeds in electric melters with results of simple laboratory experiments can help evaluate melter feed additives and their effects on melting rate, and support the feed scheduling and plant operation. A recently proposed melting rate correlation (MRC) equation, relating the melting rate to melt viscosity, feed‐to‐glass conversion heat, and cold‐cap bottom temperature, was tested using data from experiments covering various feed compositions and melter operating parameters. The MRC equation is shown to reasonably represent the measured data and thus can be used to quantify how individual variables (melt viscosity, cold‐cap bottom temperature, conversion heat, melter operating temperature, and bubbling flux) affect the glass production rate.

Description: Abstract The synthesis of high‐entropy metal carbide powders is critical for implementing their extensive applications. However, the one‐step synthesis of high‐entropy metal carbide powders is rarely studied. Herein, the synthesis possibility of high‐entropy metal carbide powders, namely (Zr0.25Ta0.25Nb0.25Ti0.25)C (ZTNTC), via one‐step carbothermal reduction was first investigated theoretically by analyzing chemical thermodynamics and lattice size difference based on the first‐principle calculations, and then the ZTNTC powders with particle size of 0.5‐2 μm were successfully synthesized experimentally. The as‐synthesized powders not only had a single rock‐salt crystal structure of metal carbides, but also possessed high‐compositional uniformity from nanoscale to microscale. More interestingly, they exhibited the distinguished coral‐like morphology with the hexagonal step surface, whose growth was governed by a classical screw dislocation growth mechanism.

Description: The fully covered by the partially dissociated species of H O exists for a wide range of temperature and the partial potential of H O. Abstract First‐principles calculations and thermodynamics analyses were combined to study the surface stabilities of 3C–SiC and H2O adsorption on the (110) surface. The stoichiometric (110) surface was predicted to be generally the most stable. Only at the extremely C‐poor condition, the nonstoichiometric Si‐terminated (100) could become more energetically favored. The adsorption and dissociation of single H2O molecule on the 3C–SiC (110) were then comparatively investigated. Calculations show that H2O molecules prefer to partially dissociate into one hydroxyl OH and one H adsorbed at the top‐most Si and C sites, respectively, leading to the formation of a hydrogen network on the surface. The calculated equilibrium adsorption diagram further suggested that the 3C–SiC (110) surface can be only either completely clean or fully covered by the partially dissociated species of H2O, for a wide range of temperature and the partial potential of H2O.

Description: Abstract Y2Si2O7 coatings were formed on Hi‐Nicalon‐S SiC fibers by reaction of solution‐derived YPO4 coatings with glass SiO2 scales formed by fiber oxidation. Two oxidation methods were used: pre‐oxidation, where fibers were oxidized prior to YPO4 coating, or post‐oxidation, where fibers were first coated with YPO4 and then oxidized. Fibers with YPO4/SiO2 films were heat‐treated in argon at 1200°C for 20 hours to react YPO4 and SiO2 to Y2Si2O7. The effects of SiO2 to YPO4 film thicknesses on fiber strength and on the Y2Si2O7formation kinetics were investigated. An optimized process to obtain single‐phase continuous Y2Si2O7 coatings on Hi‐Nicalon‐S fibers with low loss in fiber strength is suggested.

Description: With electric field amplitude (Emax), the number of cycles to fatigue failure (Ntail) varies as: Emax × = C, where a and C are constants. Similar relationships were obtained as a function of temperature, frequency and dc bias. Abstract Many devices containing ferroelectric ceramics are subjected to different loading conditions and cycles, and lack of adequate long‐term reliability studies is a major concern. Here, we explore a (Na1/2Bi1/2)TiO3–BaTiO3 solid solution and study electrical fatigue as a function of amplitude, temperature, frequency, and static offset voltage (dc bias). This is expected to act as a guide for other similar material systems. Empirical relationships to quantify the dependence of fatigue on these parameters are presented. With electric field amplitude (Emax), the number of cycles to fatigue failure (Nfail) varies as: Emax × = C, where a and C are constants whose values are different when the field amplitude is below and above the coercive field. With changes in temperature, Nfail exhibits an activated behavior and follows an Arrhenius relationship with an activation energy of 0.7 eV at an amplitude above the coercive field. In the absence of self‐heating, a power law relationship is observed between Nfail and frequency of fatigue cycles at an amplitude above the coercive field. On applying a dc bias, Nfail increases by an order of magnitude, an observation that is attributed to domain switching effects. A majority of the above‐mentioned effects have been explained in terms of the motion of domain walls under a given fatigue condition and their interaction with point defects.

Description: Abstract In recent years, BiCuSeO oxyselenides have been developed as a promising thermoelectric material. In this article, PbxBi1−xCu1−ySeO (x = y = 0, 0.02, 0.04, 0.06, and 0.08) are prepared by solid‐state reaction method and spark plasma sintering (SPS), and the combinatorial effects of Pb doping and Cu deficiencies on thermoelectric properties are investigated systematically. The transport properties are significantly enhanced due to the optimized carrier density, majorly contributing to the promotion of ZT values. As a result, the maximum ZT of 0.77 at 873 K and average ZT (from 300 to 873 K) of 0.50 are obtained for Pb0.06Bi0.94Cu0.94SeO sample. The values are 0.4 and 1.2 times, respectively, higher than that of pristine sample.

Description: Abstract Monolithic luminescent glass‐ceramic is highly desirable for solid‐state lighting as it is stable and robust, while in practical light‐emitting devices only a thin luminescent layer is used for more efficient excitation and light extraction. In this paper, Mn2+‐doped glass and glass‐ceramic with the composition of 60SiO2‐8Na2O–20ZnO–12Ga2O3 were fabricated by the conventional melt‐quenching technique. We observe that the crystallization of α‐Zn2SiO4 nanocrystals takes place on the glass surface with controllable thickness after heat treatment. The glass samples show typical red emission peaking at λ = 620 nm that can be ascribed to the spin‐forbidden 4T1g(G) → 6A1g(S) transition of Mn2+ (d5) located in the octahedral coordination site of the glass host. After surface crystallization this red emission is retained and a new green emission at 528 nm is observed through the control of the crystallization temperature and duration, thus offering tunable emission characteristics promising for the lighting application. This change in the visible emission is interpreted in terms of the change of coordination state of Mn2+ from octahedral in a glass matrix to tetrahedral in the surface precipitated α‐Zn2SiO4 crystals.

Description: Abstract The 0.97(Na0.5K0.5)(Nb1−xSbx)O3‐0.03CaZrO3 ceramic with x = 0.09 exhibits a high d33 of 518 pC/N and a strain of 0.13% at 4.0 kV/mm owing to its orthorhombic‐pseudocubic polymorphic phase boundary (PPB) structure. However, these values decreased considerably above 90°C owing to its low Curie temperature (TC), indicating that its thermal stability is not sufficient for practical applications. Li2O was added to the specimen with x = 0.11 to improve its thermal stability of the strain and d33 by increasing the TC without degrading the actual d33 and strain values. The 0.97(Li0.04Na0.46K0.5)(Nb0.89Sb0.11)O3‐0.03CaZrO3 ceramic, having an orthorhombic‐tetragonal PPB structure, exhibits a d33 of 502 pC/N and a strain of 0.16%. This large strain was maintained up to 150°C and the d33 slightly decreased to 475 pC/N at 130°C. Therefore, this lead‐free ceramic displays excellent piezoelectric characteristics with improved thermal stability, indicating that it can be applied to piezoelectric actuators.

Description: Abstract SiC‐fiber–reinforced binary Si eutectic alloy composites have been developed for aerospace applications using the melt infiltration method. In this study, the oxidation mechanisms of various binary Si eutectic alloys were evaluated at elevated temperatures. We suggest that the oxidation resistance of eutectic alloys could be predicted using the Gibbs energy change for the oxidation reaction. Based on these calculations, eutectic alloys of Si‐16at%Ti, Si‐17at%Cr, Si‐22at%Co, Si‐38at%Co, and Si‐27at%Fe were prepared. These alloys produced uniform SiO2 layers and showed the same oxidation resistance as Si at 1000°C under humid conditions. Therefore, SiC composites using Si alloys with excellent oxidation resistance can be predicted using thermodynamic calculations.

Description: Abstract Flexible antiferroelectric (AFE) Pb0.94La0.04Zr0.97Ti0.03O3 (PLZT) thick‐film capacitors were fabricated on nickel foil substrates using sol‐gel method. The thick PLZT film shows pure perovskite phase with dense microstructure. The discharge energy‐storage properties of the thick PLZT film are directly evaluated by the resistance‐inductance‐capacitance (RLC) circuit. The maximum value of the discharge energy‐storage density (Wdis) is 15.8 J/cm3 at 1400 kV/cm and 90% of the corresponding energy is released in a short time of about 250 ns. In addition, the Wdis and discharge time could be adjusted by the bent radius of the film, which provides a simple and feasible solution for the regulation of the electrical performance. Furthermore, the flexible AFE film exhibits good mechanical properties under cycling tests with bending radii down to 2.5 mm and 1500 rounds. This work shows a critical significance in fabricating flexible AFE capacitors for application in modern electronics and electrical power systems.

Description: Abstract Electron transport behavior of polymer‐derived amorphous silicoboron carbonitride (a‐SiBCNs) ceramics was studied by measuring DC/AC conductivities and optical absorption as functions of the temperature. Structural information of materials was investigated by combining X‐ray diffraction (XRD), nuclear magnetic resonance (NMR), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron paramagnetic resonance (EPR) techniques. Conductive mechanisms and electronic structure of the materials (eg, hopping mechanism, conduction band, band‐tail, and defect energy) were deduced by fitting experimental results to theoretical models. Results revealed that DC/AC conduction of materials followed band‐tail hopping mechanism instead of previously assumed variable‐range hopping mechanism. Hopping mechanism, associated with overlapped band‐tail and defect levels, was likely originated by the presence of certain number of defects and highly disordered structure of materials. The content of donor defects in materials was considered to have great influence on the type of electronic mechanism. These results were discussed in line with microstructural evolution of materials.

Description: Abstract In electric melters, the conversion heat is transferred through the foam layer at the cold‐cap bottom. Understanding cold‐cap foaming is thus important for enhancing the efficiency of both commercial and waste glass melters as well as for the development of advanced batch‐to‐glass conversion models. Observing foam behavior is still impossible “in situ,” that is, directly, in glass melters. To investigate the feed foaming behavior in laboratory conditions, we employed the feed volume expansion test, evolved gas analysis, and thermogravimetry. Combining these techniques helps assess the cold‐cap bottom temperature that directly influences the temperature gradient at the melt/cold‐cap interface, and thus the rate of melting. We also discuss the behavior of cavities formed by coalescing primary foam bubbles and ascending secondary bubbles.

Description: Abstract The focus of this study is to elucidate the role of particle size distribution (PSD) of metakaolin (MK) on hydration kinetics of tricalcium silicate (C3S–T1) pastes. Investigations were carried out utilizing both physical experiments and phase boundary nucleation and growth (pBNG) simulations. [C3S + MK] pastes, prepared using 8%mass or 30%mass MK, were investigated. Three different PSDs of MK were used: fine MK, with particulate sizes 〈20 µm; intermediate MK, with particulate sizes between 20 and 32 µm; and coarse MK, with particulate sizes 〉32 µm. Results show that the correlation between specific surface area (SSA) of MK's particulates and the consequent alteration in hydration behavior of C3S in first 72 hours is nonlinear and nonmonotonic. At low replacement of C3S (ie, at 8% mass), fine MK, and, to some extent, coarse MK act as fillers, and facilitate additional nucleation and growth of calcium silicate hydrate (C–S–H). When C3S replacement increases to 30% mass, the filler effects of both fine and coarse MK are reversed, leading to suppression of C–S–H nucleation and growth. Such reversal of filler effect is also observed in the case of intermediate MK; but unlike the other PSDs, the intermediate MK shows reversal at both low and high replacement levels. This is due to the ability of intermediate MK to dissolve rapidly—with faster kinetics compared to both coarse and fine MK—which results in faster release of aluminate [Al(OH)4−] ions in the solution. The aluminate ions adsorb onto C3S and MK particulates and suppress C3S hydration by blocking C3S dissolution sites and C–S–H nucleation sites on the substrates’ surfaces and suppressing the post‐nucleation growth of C–S–H. Overall, the results suggest that grinding‐based enhancement in SSA of MK particulates does not necessarily enhance early‐age hydration of C3S.