ALBERT

Description: The present work reports a simple, inexpensive method for synthesis of calcium hydroxide [Ca(OH) 2 ] nanoparticles (CHNPs). The method involves chemical precipitation (CP) in aqueous medium at room temperature. Calcium nitrate dihydrate [Ca(NO 3 ) 2 .2H 2 O] and sodium hydroxide were used as precursors. The CHNPs were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Rietveld analysis, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), BET surface area evaluation as well as particle size distribution analysis techniques. The results confirmed the synthesis of CHNPs as the major phase. The CHNPs exhibited an average size of about 350 nm. In addition, some calcite phase formed due to the inevitable carbonation process. A very minor amount of aragonite phase was also present. A schematically developed new qualitative model is proposed to explain the genesis and subsequent evolution of the various phases at the nanoscale. The model helps to identify the rate-controlling step. It also highlights the implication of reaction kinetics control in synthesis of predesigned nanophase assembly.

Description: The mechanical properties of dense, hot-pressed ZrB 2 –30 vol% SiC ceramics were characterized from room temperature up to 1600°C in air. Specimens were tested as hot-pressed or after hot-pressing followed by heat treatment at 1400°C, 1500°C, 1600°C, or 1800°C for 10 h. Annealing at 1400°C resulted in the largest increases in flexure strengths at the highest test temperatures, with strengths of 470 MPa at 1400°C, 385 MPa at 1500°C, and 425 MPa at 1600°C, corresponding to increases of 7%, 8%, and 12% compared to as hot-pressed ZrB 2 –SiC tested at the same temperatures. Thermal treatment at 1500°C resulted in the largest increase in elastic modulus, with values of 270 GPa at 1400°C, 240 GPa at 1500°C, and 120 GPa at 1600°C, which were increases of 6%, 12%, and 18% compared to as hot-pressed ZrB 2 –SiC. Neither ZrB 2 grain size nor SiC cluster size changed for these heat-treatment temperatures. Microstructural analysis suggested additional phases may have formed during heat treatment and/or dislocation density may have changed. This study demonstrated that thermal annealing may be a useful method for improving the elevated temperature mechanical properties of ZrB 2 -based ceramics.

Description: Si 3 N 4 -based nanocomposites containing 0–50 wt% TiC 0.37 N 0.63 are directly consolidated at 1700°C by spark plasma sintering, and their reciprocal sliding behavior against a Si 3 N 4 counterbody is investigated under a maximum Hertzian stress of 1.27 GPa in unlubricated conditions. The average grain widths of Si 3 N 4 and TiC 0.37 N 0.63 are about 85 and 90 nm, respectively. The decreasing relative densities of the as-sintered nanocomposites indicate that the nano-TiC 0.37 N 0.63 may introduce pores and reduce the hardness and fracture resistance of the materials. The brittleness index for sliding contacts in all the samples is 25–31, indicating brittle fracture taking place on the wear surface and inducing cavities. When the mean free paths of nano-TiC 0.37 N 0.63 are slightly greater than grain length of Si 3 N 4 , the best wear resistance is achieved in Si 3 N 4 containing 20/30 wt% TiC 0.37 N 0.63 due to the process of surface smoothing by triboproducts. Severe wear response can be observed in Si 3 N 4 nanocomposites containing 0, 10, 40, and 50 wt% of TiC 0.37 N 0.63 . The wear responses are explained by considering the microstructural parameters (like grain characteristics for both phases and mean free path of nano-TiC 0.37 N 0.63 ) and contact-induced fracturing behavior, as well as tribochemical reactions.

Description: In this study, a novel chalcogenide glass system, Ga–Sb–S, is reported. The glass-forming ability, the physical properties, and the structure are investigated; and the potential applications of the glasses are evaluated. The compositions consisting of ~3%–10% Ga, ~29%–37% Sb, and ~57%–63% S can form glasses. The glasses have a wide transparent window of ~0.8–14 μm, high linear refractive indices of ~2.62–2.70 (@10 μm), high third-order nonlinear refractive indices of ~12.4 × 10 −14 cm 2 /W (@ 1.55 μm), low phonon energy, and large rare earth solubility. These favorable properties make them promising materials for mid-infrared applications such as thermal imaging, nonlinear optics, and lasers.

Description: We demonstrate the resistive switching behavior on SrTiO 3 (STO) (100) single-crystalline substrate with graphene nanoribbon (GNR) electrodes. The planar GNR was fabricated on STO substrate by means of dip-pen nanolithography and polystyrene-etching techniques. The nanogap for the GNR electrodes was induced by electroburning, which was performed by applying a voltage across the GNR. The nanoscale GNR/STO/GNR RRAM device showed bipolar resistive switching behavior with low set/reset voltages and current as well as good retention characteristics. The bipolar resistive switching behavior might be attributed to roles of oxygen vacancies, originating from intrinsic characteristics of dislocation of STO single crystal.

Description: A model of reactive ion-exchange diffusion in glassy materials (glasses and glass-ceramics) has been developed. The model can be used to simulate the processes of ion-exchange-induced decrystallization of glass-ceramics and ion-exchange-induced glass crystallization. Analysis of the model in dimensionless form resulted in determining a set of dimensionless complexes comprising dimensional parameters of the ion exchange system (diffusivity, rate constant of grain dissolution, initial size and composition of the crystalline grains, etc.). Numerical values of the complexes enable one, not solving the problem, to predict the composition and structure of glass-ceramic subsurface layers produced in a certain glassy material and under given ion-exchange conditions. It was shown that the developed model correctly describes experimental data on ion-exchange-induced glass-ceramics decrystallization. It appears that the model can be used in developing a new technology of optical glass-ceramics for photonic applications.

Description: Yb:(LaY) 2 O 3 ceramic samples have been sintered to almost full density in a fast microwave heating process with zero hold time. Rapid densification is observed at heating rates ranging from 50°C to 2400°C/min. The estimated value of the power absorbed in the materials per unit volume is from 10 to 400 W/cm 3 , which is similar to the processes of flash sintering under an applied dc/ac voltage. The microstructure of the sintered samples exhibits traces of a liquid-like intergranular phase. The observed flash microwave sintering effect is associated with both preferential microwave absorption and enhanced mass transport within the softened grain boundaries arising due to an elevated concentration of defects and impurities therein. The volumetric nature of microwave heating gives rise to thermal stresses which can act as an additional driving force for sintering. The advantage of the microwave flash sintering process is that no electrodes are needed to supply the power to the articles undergoing sintering.

Description: High-temperature aero-thermal heating in a 30 kW inductively coupled plasma torch was used to replicate the effects of harsh oxidizing environments during hypersonic atmospheric entry on fracture behavior and microstructure of two-dimensional woven SiC fibers. Hi-Nicalon SiC woven cloths were exposed to surface temperatures over 1400°C with different high-enthalpy dissociated oxygen and nitrogen plasma flows, and were subsequently deformed in pure tension at room temperature. Changes in fiber microstructure and surface chemistry after thermal exposure were examined by scanning electron microscopy. Pure nitrogen plasmas resulted in a 50% decrease of strength in woven SiC fibers with minimal effects on the fiber structure, except for highly localized surface pitting caused by partial decomposition of silicon oxycarbonitride phase at high temperature. In contrast, exposure to dissociated oxygen and air plasmas led to severe strength reduction and embrittlement over significantly short time scales, corresponding to degradation rates up to 200 times higher than those reported with static heating at equivalent temperatures. The origin of accelerated embrittlement at microscopic scale was found related to complex gas-surface interactions and high-temperature oxidizing processes involving the formation of SiO 2 bubbles and microcracks on the surface. These findings are important for the development of outer fabric materials for new flexible thermal protection systems in space applications.

Description: Pressure-less spark plasma sintering (SPS) is a new approach during which rapid densification of ceramic nanopowder green bodies is accompanied by rapid grain growth. Although the origin of this phenomenon has not yet been fully understood significant, difference in grain growth between pressure-less and pressure-assisted SPS was expected. In this work 3Y-TZP nanopowder with average particle size of 12 nm was consolidated using two-step approach: (1) at an intermediate temperature (600°C to 1000°C) SPS warm pressing followed by (2) high temperature (1400°C to 1600°C) pressure-less SPS. The standard one step pressure-assisted SPS experiments were quoted as references. Rapid grain growth was observed during both pressure-less and standard SPS. The samples prepared by both approaches at the same sintering temperature (1400°C–1600°C) achieved identical grain size and grain size distribution, if large pores were eliminated in early stage by SPS warm pressing. The electric current, electromagnetic field, and mechanical pressure is proven to have a negligible direct influence on grain growth in 3Y-TZP ceramics at temperatures above 1000°C under standard SPS conditions.

Description: Bismuth ferrite, BiFeO 3 , is an important multiferroic material that has attracted remarkable attention for potential applications in functional devices. While thin films of BiFeO 3 are attractive for applications in nanoelectronics, bulk polycrystalline BiFeO 3 has great potential as a lead-free and/or high-temperature actuator material. However, the actuation mechanisms in bulk BiFeO 3 are still to be resolved. Here we report the microscopic origin of electric-field-induced strain in bulk BiFeO 3 ceramic by means of in situ high-energy X-ray diffraction. Quantification of intrinsic lattice strain and extrinsic domain switching strain from diffraction data showed that the strain response in rhombohedral bulk BiFeO 3 is primarily due to non-180° ferroelectric domain switching, with no observable change in the phase symmetry, up to the maximum field used in the study. The origin of strain thus differs from the strain mechanism previously shown in thin film BiFeO 3 , which gives a similar strain/field ratio as rhombohedral bulk BiFeO 3 . A strong post-poling relaxation of switched non-180° ferroelectric domains has been observed and hypothesized to be due to intergranular residual stresses with a possible contribution from the conductive nature of the domain walls in BiFeO 3 ceramics.

Description: Morphological details of calcium silicate hydrate (C–S–H) stemming from the hydration process of Portland cement (PC) phases are crucial for understanding the PC-based systems but are still only partially known. Here we introduce the first soft X-ray ptychographic imaging of tricalcium silicate (C 3 S) hydration products. The results are compared using both scanning transmission X-ray and electron transmission microscopy data. The evidence shows that ptychography is a powerful method to visualize the details of outer and inner product C–S–H of fully hydrated C 3 S, which have fibrillar and an interglobular structure with average void sizes of 20 nm, respectively. The high-resolution ptychrography image enables us to perform morphological quantification of C–S–H, and, for the first time, to possibly distinguish the contributions of inner and outer product C–S–H to the small angle scattering of cement paste. The results indicate that the outer product C–S–H is mainly responsible for the q −3 regime, whereas the inner product C–S–H transitions to a q −2 regime. Various hypotheses are discussed to explain these regimes.

Description: Rare-earth containing phosphors have been widely applied in lighting and display fields in the past century. Lower cost rare-earth free phosphors with high performance are highly desired driven by the exhaustion of rare earth resources and the requirement of cheaper production. Herein, Cu + ions doped tetracalcium phosphate (TTCP) yellow emitting phosphors with quantum yield of 21% are exploited. Particularly, ultra-broad band emission with a full width at half maximum (FWHM) about 200 nm throughout almost entire visible light region is observed for TTCP: Cu + phosphors, evidencing its promising application in high color rendering index (CRI) lighting source. White light emission with CRI value about 94.3 is generated by combining this TTCP: Cu + phosphor with commercial BaMgAl 10 O 17 : Eu 2+ blue phosphor, exhibiting superiority over the traditional trichromatic phosphors. Therefore, we predict great potential application for this cheaper rare-earth free TTCP: Cu + phosphor in high CRI lighting sources.

Description: Eu 3+ -doped tungstate Ba 2 La 2 ZnW 2 O 12 phosphors with perovskite-structure were prepared by the high temperature solid-state reaction. The X-ray powder diffraction (XRD) patterns and structure refinements indicate that the phosphors crystalized in the trigonal layer-perovskite. The luminescence properties of the phosphors were investigated such as photoluminescence (PL) excitation and emission spectra, decay lifetimes, and color coordinates. It was found that the pure host shows self-activated emission excited by the UV light. Moreover, Ba 2 La 2 ZnW 2 O 12 also shows scintillation characteristics under the X-ray irradiation. The near-UV and blue light can efficiently excite Eu 3+ -doped Ba 2 La 2 ZnW 2 O 12 phosphors inducing the strong orange–red luminescence. The optimal Eu 3+ doping concentration in this host is 40 mol%. The luminescence spectra and the luminescence color of the phosphors strongly depend on the doping levels and excitation wavelength. The different luminescence features were discussed on the base of crystal structure. Eu 3+ ions have two possible substitutions on A or B sites in this trigonal layered perovskite. The phosphor could act as a candidate for the potential application in near-UV excited white-LEDs lighting.

Description: The solubility of Co 3 O 4 , Cu 2 O, CuO, NiO, and Mn 2 O 3 in molten B 2 O 3 and Na 2 O–2B 2 O 3 has been studied at a temperature of 900°C under static conditions. The concentration of the dissolved metal oxides was determined by X-EDS and XPS elemental analysis. Uniformity of metal distribution has been confirmed using X-EDS and backscatter electron image mapping. It was found that the solubility of all metal oxides increased significantly with Na 2 O content in the B 2 O 3 solvent. The impact of a temperature increase of 150°C and the influence of K 2 O doping were evaluated and found to not cause any significant change.

Description: An original catalytic method has been proposed to synthesize carbon nanotubes (CNTs)–ZrB 2 –ZrO 2 heterostructures using ZrB 2 polymeric precursor. The pyrolysized gases from the ZrB 2 polymeric precursor are identified to be the carbon sources for CNTs growth. A parametric study is conducted to control the CNTs growth by optimizing parameters such as synthesis temperature and catalyst content. Observations show that the in situ grown CNTs are homogeneously dispersed in the powders, and the structure and the amount of CNTs are significantly dependent on the synthesis parameters. There are two kinds of grown CNTs existed in the produced hybrid heterostructures: (i) the kinking structured CNTs that are disordered and incomplete graphitization; (ii) the improved and graphitized CNTs. The ZrB 2 polymeric precursor during thermal pyrolysis provides capable of supplying substantial carbon source for CNTs nucleation and growth by homogeneous vapor–liquid–solid reactions.

Description: The setting processes in the commercial glass ionomer cement (Fuji IX Fast) and resin modified glass ionomer cement (Fuji II LC) were investigated by the dielectric spectroscopy. The changes in the real and imaginary parts of the dielectric permittivity [ε*(ω)] as well as dielectric loss (tan δ) with time for Fuji IX Fast show several distinct regions which are related to the different stages of the acid–base reaction. Interestingly, the first stage that lasts for approximately 12 min terminates with a sharp decrease in dielectric parameters which is most probably related to the instantaneous (micro)fracturing of the sample due to a rapid build–up of the shrinkage stress. On the other hand, evolution of the dielectric properties during the setting of Fuji II LC indicates fast reaction in the initial stage (within few minutes) followed by the slow gradual change as a result of the competing nature of the acid–base reaction and light-activated polymerization.

Description: The crystal structure and microwave dielectric properties of a novel low-firing compound Li 2 Mg 2 W 2 O 9 were investigated in this study. The phase purity and crystal structure were investigated using X-ray diffraction analyses and Rietveld refinement. The best microwave dielectric properties of the ceramic with a low permittivity (ε r ) ~11.5, a quality factor ( Q  ×  f) ~31 900 GHz (at 10.76 GHz) and a temperature coefficient of the resonant frequency (τ f ) ~ −66.0 ppm/°C were obtained at the optimum sintering temperature (920°C). CaTiO 3 was added into the Li 2 Mg 2 W 2 O 9 ceramic to obtain a near zero τ f , and 0.93Li 2 Mg 2 W 2 O 9 –0.07CaTiO 3 ceramic exhibited improved microwave dielectric properties with a near-zero τ f ~ −1.3 ppm/°C, a ε r ~ 21.6, a high Q u   ×  f value ~20 657 GHz. The low sintering temperature and favorable microwave dielectric properties make it a promising candidate for LTCC applications.

Description: The Al 2 O 3 –CaO–SiO 2 system provides the basis for describing many important chemical processes. Although the system has previously been extensively studied, recent advances in experimental technique have provided the opportunity to obtain accurate liquidus measurements in the low-silica region at fixed temperatures. The experimental procedures involve equilibration of high-purity oxide powder mixtures at selected temperatures, rapid quenching, and accurate measurement of phase compositions using electron probe X-ray microanalysis. The liquidus isotherms have been determined at selected temperatures between 1503 and 1873 K in the anorthite, gehlenite, pseudowollastonite, corundum, CaAl 12 O 19 , CaAl 2 O 6 , lime, Ca 3 SiO 3 , and Ca 2 SiO 4 primary phase fields. The results are compared with currently available thermodynamic model predictions of the phase chemistry.

Description: The mechanical properties of a ZrB 2 -10 vol% ZrC ceramic were measured up to 2300°C in an argon atmosphere. Dense billets of ZrB 2 -9.5 vol% ZrC-0.1 vol% C were produced by hot-pressing at 1900°C. The ZrB 2 grain size was 4.9 μm and ZrC cluster size was 1.8 μm. Flexure strength was 695 MPa at ambient, decreasing to 300 MPa at 1600°C, increasing to 345 MPa at 1800°C and 2000°C, and then decreasing to 290 MPa at 2200°C and 2300°C. Fracture toughness was 4.8 MPa·m ½ at room temperature, decreasing to 3.4 MPa·m ½ at 1400°C, increasing to 4.5 MPa·m ½ at 1800°C, and decreasing to 3.6 MPa·m ½ at 2300°C. Elastic modulus calculated from the crosshead displacement was estimated to be 505 GPa at ambient, relatively unchanging to 1200°C, then decreasing linearly to 385 GPa at 1600°C, more slowly to 345 GPa at 2000°C, and then more rapidly to 260 GPa at 2300°C. Surface flaws resulting from machining damage were the critical flaw up to 1400°C. Above 1400°C, plasticity reduced the stress at the crack tip and the surface flaws experienced subcritical crack growth. Above 2000°C, microvoid coalescence ahead of the crack tip caused failure.

Description: A new foaming route, which was imitated from the foaming of aerated foods, was used by the protein foaming method in preparing highly porous silicon nitride (Si 3 N 4 ) foams. Effects of air fraction on the structure and property of the products were investigated. It was indicated that the porosity increased with the air fraction exponentially, whereas the air fraction had little effect on the average pore sizes of Si 3 N 4 foams. Thermal conductivity of the product measured using the laser flash method decreased from 4.07 to 2.29 W/(m·K) when the porosity increased from 80.00% to 87.61%.

Description: In this study, a simple thick-film humidity sensor was fabricated by coating wet-synthesized ZnO nanorods on screen-printing interdigitated electrodes. We investigated the influence of the coating procedure on the microstructure of ZnO nanorod films and thereby on humidity sensing. The experimental results revealed that the specific surface area (SSA) decreased and the average pore size (APS) increased with increasing the sintering time and the number of coating layer. The humidity response depended significantly on the pore properties of the ZnO nanorod films. By virtue of the incipient wetness analysis, it was found that the adsorption of water molecules on the ZnO surface led to the decrease in electrical resistance even though the ZnO was rod like, n -type semiconductor. While tuning the pore structure of the ZnO nanorod film, the thick-film humidity sensor might display near-linear response in the full range of 0%–100% relative humidity (RH).

Description: A functionally graded sintered body consisting of laminated SiO 2 /Mo layers was fabricated using spark plasma sintering. A high sintered-body density was achieved using fine powders of SiO 2 (4.0 μm) and Mo (1.3 μm), which ensured no cracks were formed between layers. The highest joining stress (1.2 MPa) was found to occur at the interface between SiO 2 layers with 0 and 8 vol% Mo, with the electrical resistance decreasing rapidly when the Mo content was increased to 13 and 22 vol%. This is attributed to the use of spark plasma sintering, suggesting further work is needed to fully optimize this process.

Description: Microelectromechanical Systems (MEMS) devices typically need to be designed against a very low failure probability, which is on the order of or lower. Experimental determination of the target strength for such a low failure probability requires testing of tens of thousands of specimens, which can be cost prohibitive for the design process. Therefore, understanding the probabilistic failure of MEMS devices is of paramount importance for design. Currently available probabilistic models for predicting the strength statistics of MEMS structures are based on classical Weibull statistics. Significant advances in experimental techniques for measuring the strength of MEMS devices have produced data that have unambiguously demonstrated that the strength distributions consistently deviate from the Weibull distribution. Such deviations can be explained by the fact that the Weibull distributions are derived based on extreme value statistics, which is inapplicable to MEMS devices where the dimensions of the material microstructure are not negligible compared to the characteristic structural dimensions. This paper presents a robust probabilistic model for strength distribution of polycrystalline silicon (poly-Si) MEMS structures that could be extended to other brittle materials at the microscale. The overall failure probability of the structure is related to the failure probability of each material element along its sidewalls through a weakest-link statistical model. The failure statistics of the material element is determined by both the intrinsic random material strength as well as the random stress field induced by the sidewall geometry. Different from the classical Weibull statistics, the present model is designed to account for structures consisting of a finite number of material elements, and it predicts a scale effect on their failure statistics. It is shown that the model agrees well with the measured strength distributions of poly-Si MEMS specimens of different sizes, and the calibrated mean strength of the material element is consistent with the theoretical strength of silicon. Meanwhile, it is shown that the two-parameter and three-parameter Weibull distributions cannot provide optimum and consistent fits of the observed size-dependent strength distributions, and thus have very limited prediction capability. The present model explicitly relates the strength statistics to the size effect on the mean structural strength, and therefore provides an efficient means of determining the failure statistics of MEMS structures.

Description: The conduction parameters related to dc conductivity and electric modulus formulation in the temperature range 313–533 K for x Li 2 O (100 −  x ) (50V 2 O 5. 20 Bi 2 O 3 . 30 ZnO) glass system have been studied. The temperature-dependant dc conductivity is analyzed using the Mott's model for transition metals and modified Mott's VRH model. It is observed that Mott's model is in good agreement with the experimental data in high- and intermediate-temperature region as a strong electron–phonon interaction seems to be prevalent. The conduction in these glasses has been attributed to small polaron hopping at the vanadium sites in nonadiabatic regime. The ion-polaron effect (coupling between ions and polarons) leads to drop of the effective mobility and it can manifest itself as decrease in the dc conductivity with the addition of lithium content. The composition and temperature dependence of imaginary part of electric modulus ( ) collapsed onto a single master curve, confirms the presence of same type of relaxation phenomenon in all the studied glass compositions.

Description: Enhancing the performance of dielectric capacitors toward higher energy density and higher operating temperatures has been drawing increased interest. Therefore, in this investigation, research efforts were dedicated to the fabrication and characterization of nanocomposites in order to enhance the energy density at both room temperature and elevated temperature. The dielectric capacitors are fabricated using nanocomposites composed of BaTiO nanoparticles with polyimide (PI) matrix aiming at combining the high relative dielectric permittivity of the ceramic filler and the high breakdown strength of the polymeric matrix. Dielectric energy storage performance is assessed for nanocomposites with volume fractions ranging from 0 to 20% under operating frequency from 20 Hz to 1 MHz and temperatures ranging from 20 to 120 C. It is observed that with the increase of temperature, the capacitance increased while the energy density slightly decreased but significantly higher than pure polymer samples. The highest energy density was found for BaTiO /PI nanocomposites with 20% volume fraction, 9.63 J/cm at 20 C and 6.79 J/cm at 120 C. Overall, testing results indicate that using nanocomposites of BaTiO /PI as a dielectric component shows promise for implementation to preserve high energy density values up to temperatures of 120 C.

Description: The possibility of the application of fluorescence-based detection method in a microfluidic system is discussed. It consists of a microfluidic module and complementary housing. Both parts are made from LTCC technology. Three microfluidic module designs are analysed. They vary by way of their constructions of a transparent window, which is used for the transmission of a fluorescence signal from the module to the photodetector integrated onto the housing. The influence of the type of materials used for optical windows on performance of the system is discussed. According to the performed measurements, a concentration as low as 0.03 ng/mL was detected.

Description: High-performance BaMgAl 10 O 17 :Eu 2+ (BAM) phosphor was prepared by a facile aqua-suspension method, based on the in situ surface charge modification of starting powders with the aid of the γ-Al 2 O 3 porous structure. When stirred in de-ionized water at 80°C, the starting powders of BaCO 3 , MgO, and Eu 2 O 3 were positive surface charged, and attracted by the porous and negative charged γ-Al 2 O 3 powders. Through the electrostatic effect, high uniformed BAM precursor was achieved after the aqua-medium was removed. Fourier transform infrared (FTIR) spectra indicated some new chemical bonds among the reactants of the BAM precursor, which improved the powder activity and made it possible to achieve high-performance BAM phosphor at a lower calcination temperature. The obtained BAM phosphor exhibited a narrow particle size distribution, enhanced crystallinity, and a short decay time.

Description: By means of dielectric permittivity, electric modulus and impedance, the dielectric properties of LiF single crystals were investigated in the temperature range of 30°C–800°C and frequency range of 50 Hz–10 MHz. Two thermally activated relaxations, R1 and R2, were observed. The relaxation R1 showing activation energy around 0.8 eV was found to be related to the Li-ion diffusion in the crystal. The relaxation R2 contains three Arrhenius segments, the low-, mid-, and high-T segments, separated by boundary temperatures of 325°C and 425°C. These segments in the order of ascending temperature were found to be associated with F 3 , F 3 + centers, F 2 centers, and F centers, respectively.

Description: Coatings with the 0.7BaTiO 3 –0.3BiScO 3 solid-solution composition were formed on palladium and single-crystal (001) SrTiO 3 substrates using a polymeric metal citrate precursor. Solutions of TiOCl 2 , Ba(NO 3 ) 2 , Sc(NO 3 ) 3 , and Bi(NO 3 ) 3 were mixed with citric acid and polymerized with ethylene glycol. Stable mixed-metal citrate solutions were formed at pH 〉 9 and used for coatings. The phase and composition of powders and coatings were characterized using DTA, TGA, SEM, TEM, and X-ray diffraction. Single-phase cubic 0.7BaTiO 3 –0.3BiScO 3 solid solutions formed at 600°C. Coatings on Pd using precursors doped with 5 wt% lithium nitrate were dense after sintering at 950°C/1 h. Coatings without lithium nitrate required 1050°C/50 h to densify. Coatings on SrTiO 3 heat-treated at 1150°C were dense but formed a (Sc,Ti)-rich second phase.

Description: This article presents electrocaloric effect in Ba 0.85 Ca 0.15 Ti 0.9 Zr 0.1 O 3 (BCTZO) using an indirect approach based on Maxwell's relations. The peak electrocaloric performance is found to be an adiabatic temperature change of 0.41 K with electrocaloric strength of 19 mK cm/kV and a heat carrying capacity of ~0.17 J/g under an electric field of 0–21.5 kV/cm. The ferroelectric hysteresis scaling relations for coercive field ( E C ), remnant polarization ( P r ), and hysteresis area (〈 A 〉) as a function of temperature ( T ) are also systematically investigated. The power-law temperature exponents are obtained for all the hysteresis parameters. The scaling relations are established as E c ∝ T −0.6584 , P r ∝ T −1.59 , and 〈 A 〉 ∝ T −1.01623 . The presented scaling relations are compared with those reported in the literature for other ferroelectric materials.

Description: Dense (~98.5%), lithium aluminum silicate glass-ceramics were obtained via the sinter-crystallization of glass particle compacts at relatively low temperatures, that is, 790–875°C. The effect of P 2 O 5 on the glass-ceramics' sinter-crystallization behavior was evaluated. We found that P 2 O 5 does not modify the surface crystallization mechanism but instead delays the crystallization kinetics, which facilitates viscous flow sintering. Our glass-ceramics had virgilite (Li x Al x Si 3-x O 6 ; 0.5 〈 x 〈 1), a crystal size 〈1 μm, and a linear thermal expansion coefficient of 2.1 × 10 −6 °C −1 in the temperature range 40–500°C. The overall heat treatment to obtain these GCs was quite short, at ~25 min.

Description: The effect of postgrowth thermal annealing on ZnO/ZnCr 2 O 4 nanocomposites synthesized by hydrothermal method has been thoroughly investigated. XRD data have clearly revealed the transformation of spinel cubic phase of ZnCr 2 O 4 to wurtzite phase ZnO and indicated the incorporation of Cr in ZnO lattice with annealing at high temperatures. Photoluminescence spectra have shown a strong dependence of emission on annealing temperatures. This work demonstrated the unique and simple route to fabricate Cr-doped ZnO and tuning of the luminescence with annealing temperature. Thus, the work has immense potential for optoelectronic and photovoltaic applications.

Description: Analyzing the temperature evolution in pressureless mold-assisted flash sintering, we found the same onset condition as in standard flash sintering: When sample's DC or AC Joule heating replaces environment's radiation heating as the dominant power input term, thermal runaway ensues. Various serial and parallel components connected to the sample, including the mold, insulation, and punches, can affect Joule heating and conduction heat loss, thus play an important role in successful mold-assisted flash sintering.

Description: This work reports the processing steps of Al 2 O 3 (1–5 vol%) nanoparticulate ( d V.50 = 13 nm) LZS glass–ceramic matrix (19.58Li 2 O·11.10ZrO 2 ·69.32SiO 2 , mol%, d v.50 = 3.5 μm) composites for production of multilayered materials with thermal expansion gradients obtained by tape casting. Suspensions were prepared in water to solids contents ranging from 40 to 47 vol% using ammonium polyacrylate as a deflocculant, and an acrylic copolymer and polyvinyl alcohol as binders. Optimum performance was achieved by sonication and controlling the rheological properties for every step of the process. To prepare the composites, different concentrations (1, 2.5 and 5 vol%) of nanoalumina were added to fresh, as-prepared LZS suspensions, by changing the solid contents as required to maintain similar viscosities. Green tapes with high uniformity, without macroscopic defects and easy to handle were sintered to relative densities between 89% and 94%. Dense and homogeneous laminates with gradual composition with increasing concentrations of alumina were obtained.

Description: A new lead-free perovskite solid solution (1− x )BaTiO 3 – x Bi(Mg 1/2 Zr 1/2 )O 3 with morphotropic phase boundary (MPB) has been developed, and its structural and dielectric properties have been investigated. Rietveld structural analysis of the X-ray diffraction data suggest a composition-dependent tetragonal ( P 4 mm ) to cubic ( ) phase transition with an intermediate, phase coexistence region, demarcating the MPB. The compositions with x ≤ 0.05 are tetragonal in the P 4 mm space group and the compositions with x ≥ 0.25 are cubic in the space group. Coexistence of monoclinic phase (space group Cm ) with tetragonal/cubic phase (space group P 4 mm / ) is observed in the MPB region for the compositions with 0.10 ≤ x ≤ 0.22. The temperature dependence of permittivity exhibits a nonrelaxor type diffuse phase transition for all the compositions across the MPB.

Description: The amorphous silica (a-SiO 2 ) and germania (a-GeO 2 ) have a wide range of applications in glass industry. Based on a previously constructed near-perfect continuous random network model with 1296 atoms and periodic boundary conditions, we extend our study to amorphous Si 1− x Ge x O 2 models of homogeneous random substitution of Si by Ge with x ranging from 0 to 1. We have calculated the structural, electronic, mechanical, and optical properties for the series by using the first-principles density functional theory methods. The x -dependence of the variations in the properties is analyzed and critically compared with available experimental data. The mass density, volume, total bond order density, bulk mechanical properties, and refractive index are found to vary linearly as a function of x . For x = 0.5, we have also constructed six different kinds of particle immersion models to test the effect of inclusion of spherical particles of one glass of different sizes in the medium of the other glass on their physical properties. It is shown that particle sizes do affect the properties of particle immersion. Our calculations provide deep insight on the properties of mixture and nanocomposites of a-SiO 2 and a-GeO 2 glasses.

Description: Hertzian testing is applied to obtain flaw distributions in two fusion-drawn glasses and two glass-ceramics. A tungsten carbide sphere (diameter either 1.0, 2.5, or 5.0 mm) was used to produce surface cracks (ring cracks and cone cracks). Two theoretical approaches were employed to describe the data. Both approaches are only descriptive for very high strength materials in which the surface flaw sizes are small (e.g., 〈1 μm). In the first, a Weibull distribution for strength was assumed, and an expression for the probability of fracture was derived based on the stress field around the indent contact area. The unique aspect of this is that the stress field used includes material that has been “probed” at loads below the fracture load. A Weibull plot with this expression shows a slope of m + 2, where m is the conventional Weibull modulus. For the four different materials, the Weibull modulus varied between 8.0 for β-quartz glass-ceramic to 14.2 for fusion drawn alumni silicate glass. The second theoretical approach employs a modification of the method of Poloniecki and Wilshaw (the PW Method) to describe the distributions of very small flaws. The modification removes the need to bin the flaw distribution data. The modified PW Method revealed distinct differences in the flaw distributions between the four materials. These differences are consistent with the different Weibull moduli determined by ranking the different materials according to flaw size. However, Hertzian testing only probes relatively small flaw sizes and thus may differ from typical tensile or bending tests; nevertheless, the method should be applicable for extremely high strength materials.

Description: A strain-induced structural phase transition and its subsequent effect on the piezoelectric properties of BZT-BCT– x CeO 2 ( x  = 0–0.1 wt%) ceramics have been reported in this manuscript. BZT-BCT– x  wt% CeO 2 lead-free piezoceramics were successfully been prepared using sol–gel method. X-ray diffraction spectra of BZT-BCT– x  wt% CeO 2 ( x  = 0–0.10 wt%) ceramics showed a purely single-phase perovskite structure and a change in crystal structure between tetragonal and rhombohedral phases with increasing CeO 2 content. The strain-induced structural phase transition has resulted in excellent piezoelectric properties, d 33  = 673 pC/N, k p ~ 56%, and T c  = 110°C for BZT-BCT–0.08 wt% CeO 2 ceramics. Greatly improved temperature stability of the piezoelectric properties has been observed over a temperature range between 20°C and 90°C. The ferroelectric–paraelectric transition temperature, T c obtained in this study is 17°C higher than those reported earlier.

Description: The oxygen nonstoichiometry of large oxygen-deficient Ruddlesden–Popper oxides La x Sr 3− x Fe 2 O 7−δ (LSFO7- x ) ( x  = 0, 0.25, 0.5) was measured by the high-temperature gravimetry and the coulometric titration. In the composition series, the P (O 2 ) dependencies exhibited typical plateaus at δ = (2−[ ])/2. Meanwhile, La 0.5 Sr 2.5 Fe 2 O 7−δ showed the smallest oxygen nonstoichiometry and was the most thermochemically stable compound against P (O 2 ), temperature, and the La content. Based on the defect equilibrium model and the statistical thermodynamic calculation derived oxygen nonstoichiometric data, the substitution of La for Sr-site can promote the forward reaction of oxygen incorporation, the backward reaction of the disproportionation of the charge carriers, and oxygen redistribution between the O1 and O3 sites, resulting in the reduction of oxygen-deficient and the lower decomposition P (O 2 ). The obtained thermodynamic quantities of the partial molar enthalpy of oxygen, , and the partial molar entropy of oxygen, , calculated from the statistical thermodynamic calculation are in good agreement with those using the Gibbs–Helmholtz equation.

Description: Microstress in reaction-bonded silicon carbide (RBSiC) has been measured using piezo-Raman spectroscopy. Compressive microstresses as high as 2 GPa exist in the silicon phase and tensile microstresses as high as 2.3 GPa exist in the SiC phase of RBSiC. This is much larger than expected for thermoelastic microstress from coefficient of thermal expansion mismatch would provide. Instead the microstresses arise from the crystallization of liquid silicon. During the reaction bonding process, not all of the silicon reacts to form SiC and there is liquid free silicon. The phase transformation of the free silicon from liquid to solid has a large volume expansion, which results in large residual microstress within the silicon and SiC phases of RBSiC.

Description: The single crystal solid-state conversion of fluorapatite-type Sr 5 (PO 4 ) 3 F (Sr-FAP) has been achieved by spark plasma sintering with the assistance of NaF additive. NaF was determined to act as both a sintering aid and impurity solute along the grain boundaries (GBs), controlling both the space charge and GB migration rate. Postsintering isothermal annealing was performed to examine the effect of DC electric field on grain growth. From the space charge potential determined from impedance spectra measurements, in combination with the theoretical contribution of space charge to grain-boundary energy reduction, it was concluded that the magnitude of the space charge in Sr-FAP is temperature dependent. As such, a moderate decrease in polycrystalline GB driving force is the main cause for the increased single crystal migration length that was observed in this study.

Description: Phase relationships of the CaO–ZnO system in equilibrium with air ( = 0.21 atm) have been studied for the first time using the equilibration/quenching/EPMA technique in the temperature range from 1000°C to 1600°C. In this study, the mutual solubility boundaries of the CaO and ZnO phases have been determined. Both CaO and ZnO have obvious solubilities in each other. The maximum solubility of ZnO in solid CaO phase is 23.21 at.% at 1535°C, and ZnO solid phase can take up to 4.81 at.% CaO at 1535°C. The eutectic point and parts of the liquidus lines have also been determined. The eutectic point was found to be at 1535°C ± 2°C and 0.6612 mole fraction of ZnO. No compound was found in this system, and there were two primary phases: halite-structured CaO (lime) and wurtzite-structured ZnO (zincite). Results from this study were compared with the CaO–ZnO phase diagram calculated by MTDATA 5.10 and its MTOX 8.1 database. The difference was significant, and the thermodynamic description of the system requires a reassessment.

Description: The method of pulsed electric current sintering (PECS) has been used to obtain dense boron carbide (B 4 C) and B 4 C-based composite materials containing tungsten boride (W 2 B 5 ). To elucidate the role of the sintering additives and the mechanism of reactive densification, three types of materials have been obtained by PECS at 1850°C and 1900°C: “pure” B 4 C, B 4 C doped with 10 wt% W 2 B 5 , and B 4 C doped with 10 wt% tungsten carbide (WC). X-ray diffraction and X-ray photoelectron spectroscopy have been used to determine crystallite size, phase changes, and the peculiarities of the chemical bonds of the densified materials. Structural and mechanical properties of the materials have been investigated using scanning electron microscopy, optical microscopy, ultrasound velocity measurements, and hardness tests. The electrochemical impedance spectra have been used to investigate the electrical properties of the PECS-ed materials.

Description: Forsterite powders with controllable morphology were synthesized using oxides as raw materials in NaCl–KCl molten salt media. The effects of MgO/SiO 2 ratio, calcining temperature, and salt/oxide ratio on the phase composition and morphology of the powders are investigated. The results indicate that single-phase forsterite powders can be synthesized from a mixture of MgO and SiO 2 with a MgO/SiO 2 molar ratio of 2:1.3 at 700°C. With the increase in calcining temperature, the powders obtained changes from an irregular to a columnar morphology. In addition, the morphology of the forsterite powders produced can also be controlled by altering the salt/oxide ratio.

Description: This work investigated the effect of MnO 2 addition on the phase structure, microstructure, and electrical properties of AgSbO 3 -modified (Li,K,Na)(Nb,Ta)O 3 (abbreviated as LKNNT-AS) lead-free piezoelectric ceramics with an optimized composition endowed with a state of two-phase coexistence. A small amount (0.1 wt%) of MnO 2 can significantly further enhance the piezoelectric property of LKNNT-AS ceramics, whose piezoelectric constant d 33 and converse piezoelectric coefficient d 33 * as well as planar electromechanical coupling factor k p reach 363 pC/N, 543 pm/V, and 0.49, respectively. The temperature stability of piezoelectricity in MnO 2 -modified LKNNT-AS samples also improved, which is associated with the more uniform and better thermally stable ferroelectric domains that were revealed by piezoresponse force microscopy.

Description: Crystalline pure NaTi 2 (PO 4 ) 3 (NTP) powder was synthesized at 700°C using a simple and low energy, hybrid inorganic–organic, steric entrapment method. Sodium nitrite (NaNO 2 ) and ammonium phosphate dibasic ((NH 4 ) 2 HPO 4 ) dissolved in water, whereas titanium (IV) isopropoxide (Ti[OCH(CH 3 ) 2 ] 4 ) hydrolyzed in water. Ethylene glycol (HOCH 2 CH 2 OH) was used as a polymeric entrapper and hydrolysis of the Ti source was hindered by its dissolution in isopropyl alcohol. The resulting NTP powder was characterized by thermogravimetric analysis/differential thermal analysis, X-ray diffractometry, scanning electron microscopy, specific surface area by Brunauer–Emmett–Teller nitrogen absorption, and particle size analysis. Furthermore, C, H, N were measured by the classical Pregl-Dumas method. The thermal expansion behavior in all { hkl } pole directions was also determined by in situ high-temperature X-ray diffraction using synchrotron radiation and was found to be in agreement with other published studies.

Description: The synthesis of scandium nitride (ScN) nanoscale crystals by dissolving N 2 into In-Sc melts is demonstrated for the first time. The crystallization mechanism of ScN from In-Sc melts is investigated. In the N 2 pressure of 0.3 MPa, the ScN yield increases with the Sc concentration in flux and the growth temperature within the range 900–1100°C, achieving a maximum value of about 70% at temperatures above 1100°C. Scanning electron microscopy evidences the growth of round-shaped ScN crystals with increasing average size from 48 to 860 nm in the temperature range of 900–1300°C. This study shows that Sc effectively promotes the dissolution of N 2 in the In-Sc melt, and In-Sc is a promising flux for the synthesis of ScN nanocrystals.

Description: In the present study, the influences of three different types of carbon (carbon black, graphite, and petroleum coke) on SiC synthesis via mechanical activation and sintering were evaluated. In this regard, the phase components, morphology, and the formation mechanism were investigated. SiC nanoparticles were detected to be formed after 4 h of milling and sintering at 1450°C, regardless of the sources of carbon. The carbon types exert their effects on the morphology of the as-synthesized particles, where carbon black leads to form rod-like SiC particles and the other two carbon types result in semi-spherical SiC particles. This is due to the dominant mechanism in the mentioned process. The rod-like particles obtained from the carbon black-containing powder were synthesized via the VSL mechanism, whereas the solid-state reactions occurred to form the SiC particles in the graphite- or petroleum coke-containing samples. In the VSL mechanism, any increase in the milling time leads to facilitate the SiC formation due to entrance of Fe debris, whereas in the other samples (graphite or petroleum coke) the procedure is reversed.

Description: Bending strength of 5 vol.% Ni/Al 2 O 3 composites as a function of testing temperature is investigated at temperatures ranging from room temperature to 1200°C. Self-healing performance at high temperatures of the composites is evaluated by conducting high-temperature bending tests for as-sintered, as-cracked, and as-healed specimens. Bending strength of as-sintered specimens dramatically decreases from 995 MPa at room temperature to 205 MPa at 1200°C. Additionally, the plastic deformation of the as-sintered specimens occurs when the testing temperature reaches to 1200°C. The values of high-temperature bending strength of as-healed specimens are comparable with those of as-sintered specimens. Similar to that of as-sintered specimens, bending strength of as-healed specimens degrades when the testing temperature increases. Results of the present study indicate that the recovery of bending strength by the self-healing function is able to achieve at temperatures as high as 1200°C. Unlike the mechanical behaviors at high temperatures of as-sintered and as-healed specimens, the bending strength of as-cracked specimens slightly increases with the increase of testing temperature. This phenomenon is attributed to the effect of the self-healing mechanism during high-temperature bending tests.

Description: Reaction-bonded silicon carbide (RBSC) was prepared by ceramic injection molding (CIM) technique with feedstocks containing silicon carbide (SiC), a wax-based organic system and different amounts of carbon black. As a critical effect of the reaction sintering process, carbon was introduced from the carbon black and the decomposition product of the organic polymers, respectively. This study described the influence of carbon content on the mixing and injection process firstly and then emphasized the debinding process since it played a large role in the process of the pyrolysis of organic. Results indicated that the preferable thermal debinding was performed in N 2 and the optimal performance was obtained for RBSC with 7 wt.% of carbon black, with the density of 2.98 g/cm 3 , apparent porosity of 0.24%, bending strength of 301.59 MPa and fracture toughness of 4.18 MPa·m 1/2 .

Description: As highly integrated circuits are demanded for high-performance electric devices, small sizes of barium titanate (BaTiO 3 ) as a dielectric material are desirable for the application of multilayer ceramic capacitors. Since the small sizes of the particles degrade the dielectric property, especially below a certain critical size, understanding the probable cause is significant for the high-performance capacitors. Here, we have demonstrated nanosized BaTiO 3 with average size below 30 nm and a uniform size distribution. High-resolution transmission electron microscopy (TEM) shows that the as-synthesized BaTiO 3 contains intragranular pores. We have analyzed the correlation between the intragranular pores inside nanoparticles and their phase ratio of cubic and tetragonal. We have found that the presence of the intragranular pores affects low tetragonality of BaTiO 3 particles, and the intragranular pores are generated by the accumulation of hydroxyl groups during hydrothermal reaction. Formation and accumulation of intragranular pores have been investigated by ex-situ synchrotron X-ray diffraction and TEM analysis, suggesting the phase evolution model of nanosized BaTiO 3 .

Description: In this study, we prepared an aqueous dispersion of fluorine-doped hydroxyapatite (FHA) nanoparticles by a wet chemical method. For the first time, the as-prepared aqueous dispersion of FHA nanoparticles was directly used as suspension for depositing nanostructured FHA coating on stainless steel substrate by suspension plasma spray (SPS) method. Field-emission scanning electron microscopy images confirm that the coating was nanostructured. X-ray Diffraction pattern, Fourier-transform infrared spectroscopy, and Raman spectra show that the as-sprayed coating was FHA phases. The experimental result confirmed that OH − and F − ions have been well kept in FHA crystal lattice and structural integrity has been maintained during SPS process by using an aqueous dispersion of FHA nanoparticles. The potentiodynamic polarization and electrochemical impedance spectroscopy results prove that the nanostructured FHA coating can greatly enhance the anticorrosion performance of stainless steel in phosphate-buffered saline solution.

Description: We report a novel joint fabrication method for YBa 2 Cu 3 O 7− x (Y123) bulk superconductors without pressure loading, based on a well-controlled high-temperature process. Due to the direction of the heat fluxes in a box furnace, the surfaces of the joined samples melt first, and the crystal morphology of the original YBa 2 Cu 3 O 7− x bulks remains. After the joining process, part of the texture zone is used as a seed to grow new texture crystals for nucleation during cooling. Finally, a high-quality artificial grain boundary forms without acting as a weak link, which is supported by the trapped field distribution. Details of the joint are presented, including its microstructure and micro-orientation. Moreover, the trapped field values at 65 and 45 K are presented.

Description: A comparison between 2D and 3D Finite Element Method based simulations on the tunability properties of ferroelectric – linear dielectric composites is presented. Dependences of the effective permittivity and tunability on the concentration of the linear phases are presented and it is shown that there are important differences between the two approaches. The appropriateness of such simulations in describing realistic composite systems is discussed, too.

Description: A novel molten-salt and microwave coassisted carbothermal reduction (termed as MSM-CTR) method was developed to prepare ZrB 2 powders from raw materials of ZrO 2 , B 4 C, and amorphous carbon. The results indicated that the carbothermal reduction reaction for synthesizing ZrB 2 was initiated at the temperature as low as 1150°C, and phase pure ZrB 2 powders were obtained after only 20 min at 1200°C, which were significantly milder than that of the conventional CTR method as well as the modified CTR method even using active metal as additional reducing agents. More interestingly, the as-obtained ZrB 2 powders consisted of well-defined single-crystalline nanorods, which had diameters of 40–80 nm and high aspect ratios of 〉10. These results demonstrated that the MSM-CTR is a simple and efficient route for preparation of high-quality ZrB 2 powders.

Description: Oxide glasses exhibit slow crack growth under stress intensities below the fracture toughness in the presence of water vapor or liquid water. The log of crack velocity decreases linearly with decreasing stress intensity factor in Region I. For some glasses, at a lower stress intensity, K o , log v asymptotically diminishes where there is no measurable crack growth. The same glasses exhibit static fatigue, or a decreasing strength for increasing static loading times, as cracks grow and stress intensity eventually reaches the fracture toughness. In this case, some glasses exhibit a low stress below which no fatigue/failure is observed. The absence of slow crack growth under a low stress intensity factor is called the fatigue limit. Currently, no satisfactory explanation exists for the origin of the fatigue limit. We show that the surface stress relaxation mechanism, which is promoted by molecular water diffusion near the glass surface, may be the origin of the fatigue limit. First, we hypothesize that the slowing down of slow crack growth takes place due to surface stress relaxation during slow crack growth near the static fatigue limit. The applied stress intensity becomes diminished by a shielding stress intensity due to relaxation of crack tip stresses, thus resulting in a reduced crack velocity. This diminishing stress intensity factor should result in a crack growth rate near the static fatigue limit that decreases in time. By performing Double Cantilever Beam crack growth measurements of a soda-lime silicate glass, a decreasing crack growth rate was measured. These experimental observations indicate that surface stress relaxation is causing crack velocities to asymptotically become immeasurably small at the static fatigue limit. Since the surface stress relaxation was shown to take place for various oxide glasses, the mechanism for fatigue limit explained here should be applicable to various oxide glasses.

Description: Strontium barium niobate (SBN) is a tungsten bronze family ferroelectric which shows promising thermoelectric properties under reducing conditions. It is found here that the enhanced electrical conductivity of oxygen-deficient SBN correlates with the formation of a NbO 2 secondary phase. The effects of the reducing environment and the NbO 2 phase formation are studied via a detailed defect chemistry analysis. Increasing amounts of the NbO 2 phase are accompanied by an interesting mechanism where the A-site occupancy of the SBN matrix increases. The resulting donor defects source the large carrier concentrations which cause the enhanced electrical conductivity necessary for thermoelectric performance. In investigation of the phase equilibria, it is found that a solid solution between (Sr 0.6 ,Ba 0.4 )Nb 2 O 6 and (Sr 0.6 ,Ba 0.4 ) 1.2 Nb 2 O 6 exists and that the A-site filling is found to occur at more modest reduction conditions in Sr- and Ba-rich compositions. Finally, thermogravimetric analysis of the reoxidation process is performed, and the results suggest that the A-site filling is compensated ionically. Not only do the presented results explain the enhanced electrical conductivity of oxygen-deficient strontium barium niobate but also modification of the site occupancies by reduction and reoxidation may widen the design space for property modification in tungsten bronze-structured materials in general.

Description: This study evaluates the change of flow stress as related to dislocation density in SrTiO 3 single crystals in order to provide guidance for later electrical studies. The key parameters varied are temperature and loading rate during the deformation. It is found that in 〈100〉-oriented SrTiO 3 single crystals, the dislocation density is enhanced by plastic deformation, more so at higher temperature as compared to room temperature. The experimental approach of quantifying the dislocation density through a determination of ex situ X-ray diffraction rocking curves was successfully applied over the upper temperatures region of the lower temperature ductility zone for strontium titanate, i.e., in the so-called “A-regime”. For 1.0% deformed samples deformed at 300°C, a fourfold increase in dislocation density to 1.4 × 10 13  m −1 was found as compared to the nondeformed state (3.7 × 10 12  m −1 ). Cross-section techniques confirmed that the observed dislocation densities measured at the surfaces were identical to those seen in the core of the crystals. The use of rapid changes in loading rate provided an estimate for activation volume of the dislocation core for both 25°C and 300°C.

Description: To understand the potential for use of the Hf–Al–C ternary compounds, (HfC) n Al 3 C 2 (Hf 2 Al 3 C 4 and Hf 3 Al 3 C 5 ) and (HfC) n Al 4 C 3 (Hf 2 Al 4 C 5 and Hf 3 Al 4 C 6 ) were investigated using density functional theory, including crystal structure, electronic structure, compressibility, and elastic properties. The theoretical density of (HfC) n Al 3 C 2 (4.10–4.16 g/cm 3 ) is higher than that of (HfC) n Al 4 C 3 (3.92–3.98 g/cm 3 ), due to the smaller number of lighter Al–C layers. With increasing numbers of Hf–C layers, the Hf–C and Al–C bond lengths remain almost unchanged. In none of the compounds is there a gap around the Fermi energy ( E f ), which implies they are metal-like conductors. With increasing pressure, there is greater shrinkage along the c axis than the a axis. The bond stiffness increases with increasing pressure. In general, (HfC) n Al 3 C 2 has higher elastic stiffness than (HfC) n Al 4 C 3 , with the moduli increasing with the number of Hf–C layers. The Hf–Al–C compounds as well as the brittle Zr–Al–C compounds all have low shear moduli/bulk moduli ratio ( G / B ) from 0.71 to 0.78, suggesting that the G / B ratio is not always a suitable measure of ductility.

Description: Inorganic coatings are being developed to protect marble monuments and sculpture from weathering. In this work, the acid resistance of hydroxyapatite (HAP), calcium oxalate, and calcium tartrate coatings on Carrara marble were compared. To quantify the rate of attack on calcite, the pH of the solution was measured. This approach was validated by confirming that the rate of dissolution of untreated calcite inferred from the change in pH agrees with data in the literature. Calcium tartrate coatings were incomplete, and the mineral is so soluble that it offered no significant protection. Calcium oxalate forms coherent coatings, so it serves as a sacrificial coating in spite of having solubility comparable to that of calcite. HAP was deposited from aqueous solutions of 1 M diammonium hydrogen phosphate (DAP), with or without millimolar additions of CaCl 2 (which improved coverage) and (NH 4 ) 2 CO 3 (which resulted in cracking). The best HAP coatings remained porous; nevertheless, they were comparable to oxalate coatings in the short term and superior in the long term, reducing the dissolution rate by about 40%.

Description: Ceria-stabilized zirconia (CSZ) microspheres of ~100 μm were prepared by external gelation process. The inner diameter of nozzle was 0.2 mm. The key process parameters including broth pH value, Zr concentration, flow rate, and vibration frequency were optimized for precise control of the diameter. The optimum parameters were found to be flow rate of 11.08 mL/min, Zr concentration of 0.72 mol/L, and vibration frequency of 2650 Hz. CSZ microspheres with an average diameter of 103.1 μm and standard deviation of 4.4 were prepared under these conditions. CSZ microspheres showed good monodispersity, good sphericity, and high density.

Description: Infrared transparent ceramics found to have numerous civilian and defense applications. In the present work, Y 3 Al 5 O 12 nanoparticles were synthesized by an auto-igniting modified single-step combustion method. The structure and morphology of the as-prepared powder revealed the phase purity and ultrafine nature of the powder having an average crystallite size of 16 nm and well-defined lattice planes. Coupling of the resistive and microwave heating at precise proportion leads to a sintered density of the powder with 99.3% of the theoretical density at a temperature as low as 1470°C for a soaking duration of just 20 min. Marked reduction in grain size and the porosity was also observed for the hybrid sintered pellets. An average grain size of 167 nm was measured for the sintered pellets, which also showed a high transmittance of 80% in the UV–vis region and 82.5% in the mid-IR region.

Description: Single-phase, c -axis-oriented BiCuSeO thin films have been directly grown on the commercial silicon (001) wafers without any surface pretreatment by using pulsed laser deposition. X-ray diffraction pole figure confirms that the film does not have any ab- plane texture, whereas cross-sectional transmission electron microscopy shows good crystallinity of the film even if there exists an amorphous native oxide layer on the wafers surface. At room temperature, the resistivity of the film is about 14 mΩ cm, which is much lower than that reported for corresponding single crystals as well as polycrystalline bulks. This work demonstrates the possibility of using the available state-of-the-art silicon processing techniques to create BiCuSeO-based thin-film thermoelectric devices.

Description: An approach to improve the lifetime of air plasma sprayed (APS) thermal barrier coatings (TBCs) by modifying the interfacial microstructure has been reported. The laser powder deposition technique was employed to fabricate the mesh structure (with the same composition as the bond coat) at the ceramic–substrate interface. After thermal cycling test, the APS TBCs with the mesh exhibited a much less spallation degree (5%–10%) compared with the reference samples without mesh (〉50%), implying that the mesh is effective in impeding the crack propagation along the interface. In addition, the effect of the mesh geometry parameters, e.g., height and spacing of mesh, on the spallation degree of TBCs was also investigated. Based on the results of experiment and calculation, the optimal mesh parameters were proposed.

Description: (Cr 2 Ti)AlC 2 is a newly discovered MAX phase with ordered occupations of Ti and Cr atoms on M sites. The Cr-containing MAX phase is expected showing magnetic property, which provides functional applications in spintronics and as self-monitoring smart coating. The magnetic states of (Cr 2 Ti)AlC 2 are predicted by GGA and GGA +  U methods and compared to those of Cr 2 AlC. The ground states are predicted as FM or AFM-XX configurations depending on the calculation methods. Analysis of the electronic structure shows that the magnetic moments mainly originate from the net spins of Cr 3 d valence electrons, whereas the contribution of other atoms is negligible. The calculated magnetic moments of Cr atoms in (Cr 2 Ti)AlC 2 are higher than those in Cr 2 AlC due to the larger distance between the out-plane Cr atoms separated by the intercalated nonmagnetic Ti–C slab. This work provides an insight on tailoring magnetic properties of MAX phases by modifying the crystal structure.

Description: A two-step solid-state reaction is proposed to synthesize monophasic cobalt tellurate Co 3 TeO 6 (CTO), a type II multiferroic, using Co 3 O 4 and TeO 2 as the starting reagents. First step of the reaction results in the secondary monoclinic ( P 2 1 / c ) CoTeO 4 compound, which on further calcination (second step) leads to the primary monoclinic ( C 2/ c ) Co 3 TeO 6 phase. High-resolution synchrotron X-ray diffraction and the subsequent Rietveld analysis are used to probe different phases present in the synthesized CTO and to achieve its single phase. X-ray absorption near-edge structure studies at Co K and Te L edges reveal mixed oxidation states (Co 2+/3+ ) of Co and hexavalent Te, respectively. Charge imbalance due to mixed valence Co ions has been attributed to cations vacancies. Enhanced multiferroic properties, such as effective magnetic moment, spin phonon coupling, etc., have been attributed to the aforementioned observations in grown ceramic CTO via proposed synthesis route.

Description: Low-temperature conductivity mechanisms were identified in acceptor-doped SrTiO 3 single crystals quenched from high temperatures under reducing conditions. Impedance spectroscopy measurements made on samples of the prototypical perovskite structure doped with iron provided a framework for creating a complete conductivity model for a well-defined point defect system. The dominant conductivity mechanism in the room-temperature range was identified as being controlled by oxygen vacancy hopping. The activation energy for oxygen vacancy migration, an often debated value in the perovskite community, is determined to lie within the range of 0.59–0.78 eV for the iron-doped system with the bottom of this range approaching the intrinsic value for oxygen vacancy hopping in an undoped single crystal. At low temperatures, oxygen vacancies form defect complexes with iron impurities, and the observed range of activation energies is explained and modeled in terms of an oxygen vacancy trapping mechanism.

Description: In this study, the influence of the shape of the doctor blade on the flow inside the tape casting unit and on the resulting tape properties is investigated both numerically and experimentally. Using the results from the analysis of the produced tape and from the simulations of the flow inside the tape casting unit, the relationships between blade geometry and the particle orientation in the resulting tape, as well as the resulting tape thickness, are shown. Additionally, the experimentally and numerically obtained results were compared to an analytical model for the prediction of the tape thickness. The simulations were carried out using the particle-based smoothed particle hydrodynamics method using a non-Newtonian fluid model to describe the ceramic slurry. Both in experiment and simulation, the influence of the blade geometry on the resulting tape shows good agreement.

Description: Na 0.5 Bi 0.5 TiO 3 (NBT) platelets with high aspect ratio were synthesized from Na 0.5 Bi 4.5 Ti 4 O 15 (NBIT) precursors via a topochemical microcrystal conversion in molten salt conditions. The effect of the synthesis parameters, such as the molten salt system, synthesis temperature, and the molar ratio of Na 2 CO 3 and NBIT, was investigated. The results showed that NaCl–KCl molten salt environment and excess Na 2 CO 3 played a positive role in the synthesis, square-shaped NBT was obtained at 950°C in NaCl–KCl molten salt and a TiO 2 -free environment, and it was a suitable template candidate to achieve NBT-based textured ceramics using the reactive template grain growth (RTGG) method.

Description: The crystallization mechanisms for Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) glass ceramics were studied using thermophysical property characterization techniques. Differential scanning calorimetry (DSC) revealed two separate exothermic events that were ascribed to the initial growth and growth to coherency of a dendritic phase. It was found that the commonly used Johnson-Mehl-Avrami is not a suitable kinetic model for this material. Rather, the Sestak-Berggren (SB) autocatalytic kinetic model was used to analyze the DSC data and the activation energy for initial growth (259 kJ/mol) and coherency (272 kJ/mol) was calculated using isoconversional methods. The calculated parameters for the SB model were used to compare experimental and calculated values for heat flow during the crystallization of LATP and good fits were found for both exothermic events.

Description: An environment friendly nonlinear chalcogenide glass fiber with a Ge-Sb-Se core and a Ge-Se cladding is fabricated for bright broadband mid-infrared (MIR) supercontinuum (SC) generation. The fabricated Ge-Sb-Se/Ge-Se fiber with a core diameter of 6 μm shows zero group velocity dispersion at ~4.2 μm and ~7.3 μm. By pumping the fiber with a length of 11 cm at 4.485 μm with 330 fs pulses, we achieve a SC covering the 2.2–12 μm spectral range and with an output average power of ~17 mW. This bright broadband SC source is promising for high-resolution MIR spectroscopy.

Description: CeO 2 /CoPc nanocomposites were synthesized by simple chemical method. Thermal behavior of these nanocomposites was studied by thermogravimetric and differential thermal analysis. The as-synthesized nanocomposite samples were characterized by various techniques. A decrease in band-gap energy together with an improved absorption intensity of the composite material confirms the role of the cobalt phthalocyanine in the absorption properties of CeO 2 /CoPc composite. This study confirms structural modifications and extended spectral response of the synthesized CeO 2 /CoPc nanocomposites. The results demonstrate that CeO 2 /CoPc nanocomposite samples are promising materials for organic light-emitting diodes, solar cells, and optoelectronic devices.

Description: Fully dense (TiB 2 + SiC) reinforced Ti 3 SiC 2 composites with 15 vol% TiB 2 and 0–15 vol% SiC were designed and synthesized by in situ reaction hot pressing. The increase in SiC content promoted densification and significantly inhibited the growth of Ti 3 SiC 2 grains. The in situ incorporated TiB 2 and SiC reinforcements showed columnar and equiaxed grains, respectively, providing a strengthening–toughening effect by the synergistic action of particulate reinforcement, grain's pulling out, “self-reinforcement,” crack deflection, and grain refining. A maximum bending strength of 881 MPa and a fracture toughness of 9.24 MPam 1/2 were obtained at 10 vol% SiC. The Vickers hardness of the composites increased monotonously from 9.6 to 12.5 GPa.

Description: SiO 2 -CaO-P 2 O 5 -based mesoporous bioactive glass (MBG) is a potential material for bone implants due to its superior bioactivity. Sol-gel is a common technique for preparing MBG. Early studies showed that for MBG, the composition and surface area have critical influences on the bioactivity of MBG. However, there is a counteractive effect if both factors are used to enhance the bioactivity of MBG: a higher Ca content (lower Si content) provides more nonbridging oxygen groups, which enhance the bioactivity, but a higher Ca content also allows a lower viscosity at high temperature. Low viscosity is not able to prevent the MBG liquid flowing into the mesopores and results in the reduction of the surface area, which deteriorates the bioactivity. Unlike sol-gel, spray pyrolysis (SP) offers a rapid cooling rate, which can avoid the lower viscosity and resultant damage to the mesoporous structure, and the rapid cooling rate also preserves more metastable siloxane groups, which enhance the bioactivity. In this study, MBG particles with various Si:Ca ratios were synthesized using SP, and the morphology and bioactivity were investigated. Two typical morphologies, spherical mesoporous and wrinkled mesoporous, were observed. Also, a faster hydroxyl apatite formation time was observed in MBG with lower silica concentration (70 mol% SiO 2 ).

Description: Dielectric composite thick films containing a high dielectric constant CaCu 3 Ti 4 O 12 (CCTO) filler in a UV-cured polymer matrix were investigated as flexible planar capacitors on Cu foils. Dielectric performance depended on the volume fraction and size of CCTO particles dispersed in the cured polymer matrix. As a result, the thick films containing 33.3 vol.% CCTO with an average particle size of 0.47 μm exhibited a dielectric constant of ~80 and a dielectric loss of ~0.06 at 10 kHz. The effective medium theory model incorporating a morphology fitting parameter has been proven to be most close to the experimental values.

Description: The modified sol–gel method was used to synthesize lead zirconate titanate nanoparticles, and the lead zirconate titanate nanoparticles and polyvinylidene fluoride were used to prepare piezoelectric nano-ceramic–polymer composites with 0–3 connectivity type. The composites were successfully prepared by cold-pressing and curing-molding methods. X-ray diffraction and scanning electron microscopy were adopted to characterize the microstructure of the obtained lead zirconate titanate nanoparticles and composites. The normal vibration modes of the lead zirconate titanate nanoparticles were investigated by Fourier transform infrared spectroscopy. The dielectric and piezoelectric properties of the composites were analyzed in detail with respect to different volume fractions of the lead zirconate titanate nanoparticles. It demonstrated that the values of d 33 and ε increased with the increase in the content of lead zirconate titanate. The results here pointed to potential and simple methods to fabricate the lead zirconate titanate nanoparticles and the piezoelectric ceramic–polymer composites for piezoelectric applications.

Description: SiC-based composites exhibit oxidative embrittlement at intermediate temperatures. Although the mechanisms of internal oxidation in composites with initially hermetic matrices have been studied extensively, comparable studies on composites with semipermeable matrices, such as those produced by polymer infiltration and pyrolysis, have not been reported. The present article focuses on the latter class of composites, specifically a SiC f /SiCN m with a dual BN/Si 3 N 4 fiber coating. It describes detailed SEM and TEM analyses of the microstructure before and after oxidation in dry air or water vapor at 800°C. The results show that internal oxidation is more aggressive in water vapor and occurs appreciably even in the absence of an applied stress. The sequence of oxidation of the constituent phases appears to be consistent with the underlying thermodynamic hierarchy for the respective oxidation reactions. Notably, contrary to existing models based on preferential oxidation of BN coatings, oxidation occurs first on the SiC fiber surfaces and the Si 3 N 4 overcoat; crystalline BN remains even after significant fiber and matrix oxidation has occurred. The results are discussed in terms of rate-controlling kinetic processes, the effect of oxidant type, and applied stress.

Description: Ultralight Si 3 N 4 ceramic foams have been successfully prepared through particle-stabilized foams method, which is based on the adsorption of in situ hydrophobized Si 3 N 4 particles to the liquid/air interface of the foams. Here, we firstly used a long-chain surfactant cetyltrimethylammonium chloride to render the Si 3 N 4 particles partially hydrophobic. By tailoring the surfactant concentration and pH values of the suspensions, the wet foams were stabilized to avoid coarsening and coalescence. SEM results show that the Si 3 N 4 ceramic foams possess single strut walls with elongated β-Si 3 N 4 grains interlocking with each other, and their pores are uniform with an average pore size of 95 μm. The obtained ceramic foams maintain compressive strength of 1.34 ± 0.13 MPa with porosity of 92.0%, when the suspension contains 3 mmol/L surfactant at the pH of 11.0.

Description: Mullite whiskers frameworks with an ultrahigh porosity were fabricated by the vapor-phase reaction of AlF 3 , Al 2 O 3 , and SiO 2 and adding expandable mesocarbon microbeads (MCMB) as a pore-forming agent. A large volume expansion of 122% for MCMB due to its layered structure occurred during the formation of mullite whiskers, resulting in the expansion of samples and high porosities of 87.7%–98.2% at 50–90 wt% MCMB contents. Perfect whiskers and a lap-joint structure formed due to the formation of mullites through the vapor-phase reaction. A bimodal pore structure was achieved from the spaces of the whiskers framework and burning of the expanded MCMB. High compressive strengths of 1.7 to 5.4 MPa were obtained for the porous mullite at porosities of 94.2%–87.7%, which suggested a rigid structure; these strengths at the ultrahigh porosities are attributed to the merit of the framework with high strength whiskers and their strong bonding.

Description: A specimen having a stoichiometric composition of KSbO 3 ·(KSb) calcined at 800°C has an R rhombohedral structure (RS), and changes to a Pn cubic structure (CS) when calcined at 1100°C. Finally, a 〈111〉-oriented rhombohedral phase is formed in the specimen calcined at 1230°C. K/Sb ratio decreases from 1.0 in RS, 0.93 in CS, and finally to 0.85 in 〈111〉-oriented rhombohedral phases. On the other hand, a specimen having a K-excess composition of K 1.1 SbO 3 calcined at 800°C shows a RS that is maintained in the K-excess specimen calcined at 1230°C. The composition of these specimens is very close to KSb. Therefore, the RS with a space group of R is a stable form of KSbO 3 . The formation of Pn cubic and 〈111〉-oriented R phases can be explained by the evaporation of K 2 O during the calcination process at temperatures above 1100°C.

Description: Forsterite (Mg 2 SiO 4 ) was chosen as a new candidate for bone implant application because of its superior fracture toughness and good bioactivity. However, synthesizing pure forsterite has been a challenge to many researchers because of its inability to eliminate secondary phases that have similar chemical compounds as forsterite. Attritor mill was introduced to form pure forsterite via solid-state method through the reaction between magnesium carbonate (MgCO 3 ) and talc (Mg 3 Si 4 (OH) 2 ). Attritor-milled samples showed superior mechanical properties compared with ball-milled samples because of the smaller particle size of the former which in turn eliminated the secondary phases at low sintering temperature.

Description: Praseodymium nickelate (Pr 2 NiO 4 ) is an active oxygen electrode for solid oxide fuel cells, but undergoes phase transition at elevated temperatures (e.g., 750°C). Quantification of this phase evolution in an operating single cell is challenging because of the overlap of X-ray diffraction (XRD) peaks between the cathode and oxide current collector. In this work, we replace the oxide current collector with a gold metal grid, circumventing these challenges by allowing the exposure of the cathode to the X-ray beam, while eliminating peak overlap. Quantification of the phase evolution was performed by a least-squares fitting of the linear combination of XRD standards against the experimental patterns. Energy-dispersive spectroscopy analysis on long-term operated cells showed the absence of reactions between the gold grids and the cathodes. Additionally, the grids exhibited excellent mechanical stability under operating conditions and enabled similar cell performance as an oxide current collector.

Description: Carbon–carbon (C/C) composite is one of the best ceramic matrix composite due to its high mechanical properties and applications at control environments in various sectors. Carbon–carbon composite is made of woven carbon fibers; carbonaceous polymers and hydrocarbons are used as matrix precursors. These composites generally have densities 〈2.0 g/cm 3 even after densification. C/C composites have good frictional properties and thermal conductivity at high temperature. Also C/C composite can be used as brake pads in high-speed vehicles. In spite of various applications, C/C composites are very much prone to oxidation at high temperature. Therefore, C/C composites must be protected from oxidation for the use at high temperature.

Description: Spinel materials of composition Zn 1− x Cu x Al 2 O 4 (ZCA, x = 0–0.015) were prepared via the conventional solid-state route. The lattice structure, microstructure, and microwave dielectric properties were investigated as a function of Cu content. Cu doping was found to improve the sinterability and, meanwhile, significantly increase the quality factor ( Q × f 0 ), which is due to the Cu-O bond is stronger than Zn-O bond, and inhibit the oxygen vacancy considered to be responsible for the enhanced Q × f 0 value of ZCA materials. The best microwave dielectric properties were obtained in Zn 0.99 Cu 0.01 Al 2 O 4 with ε r = 8.69, Q × f 0 = 69,300 GHz and τ f = −58.3 ppm/°C, which was sintered at 1520°C for 3 h in air.

Description: Crystal s tructures, characteristics, and preparations of 12CaO·7Al 2 O 3 family and CaO–Al 2 O 3 (C–A) system have been reviewed in detail with relevant thermodynamic parameters being assessed or recalculated. 12CaO·7Al 2 O 3 (shortened as C12A7) can form several derivatives of type C12A7:M n− or C12A7–M n− through replacing so-called “free oxygen ion” by many anions including OH − , H − , O − , , F − , Cl − , and e − in their cages, or being adopted by rare earth metals or alkaline earth metal oxides at cation sites (Ca 2+ or Al 3+ ). These doped C12A7 derivatives show unique material properties of transparent conduction, catalysis, and antibacterial with potential applications in fast ion conductors, optoelectronics, oxidants, and catalysts etc.

Description: Li 2 O–MgO–TiO 2 ternary system is an important microwave dielectric ceramic material with excellent properties and prospect in both scientific research and application. A phase diagram of the Li 2 O–MgO–TiO 2 ternary system was established in this article, based on earlier research results and our present work. Microwave dielectric properties with compositions in different regions of the phase diagram have been analyzed. We found that the 0.33 Li 2 MgTi 3 O 8 –0.67 Li 2 TiO 3 ceramics sintered at 1200°C exhibited excellent dielectric properties: Q × f value = 80 476 GHz (at 7.681 GHz), ε r = 24.7, τ f = +3.2 ppm/°C. We also designed two ceramic systems in the Li-rich region of the Li 2 O–MgO–TiO 2 ternary system, which received little attention in the past decades, because many excellent single-phase ceramics, such as Li 2 MgTiO 4 , Li 2 MgTi 3 O 8 and MgTiO 3 , have been found in the Ti-rich region. The ceramic systems have low sintering temperatures but also relatively poor dielectric properties.

Description: Through a careful composition design, new oxyfluoride glass-ceramics (GCs) containing BaLiF 3 nanocrystals with sizes of around 30 nm were prepared. Microstructural characterizations show interpenetrating phase separation in the sample with a composition of 15BaF 2 –15ZnF 2 –70SiO 2 , after thermal treatment at 580°C for 40 h which leads to the nanocrystallization of BaLiF 3 . The BaLiF 3 nanocrystals embedded in the glassy matrix could provide Ba or Li sites for the incorporation of optically active rare earth and transition-metal ions, which provides a possibility to explore novel photonic properties by the codoping of rare earth and transition-metal ions in GC materials.

Description: The process–microstructure relationship in suspension plasma spray (SPS) of yttria partially stabilized zirconia (YSZ) has been studied experimentally. An ethanol-based suspension with a powder loading of 25 wt% was plasma sprayed with radial injection under four different plasma conditions, to examine the effects of plasma gas composition (Ar/He ratio), secondary gas (Ar/He and Ar/H 2 ), and the nozzle diameter of the plasma gun. The suspension feeding rate was optimized firstly and coatings were prepared for microstructural observation. Capturing of in-flight particles into water as well as collection of splats formed on heated flat metal substrates were utilized in order to better understand the more complicated intermediate process steps in SPS. It was found that a plasma jet with higher momentum allowed a higher suspension flow rate and both columnar and deep vertically cracked structure could be created depending on the plasma parameters as well as the substrate surface roughness.

Description: CsPbBr 3 quantum dots were precipitated in phosphate glasses through heat treatment. Controlled formation of CsPbBr 3 quantum dots was realized by adjustment of heat-treatment conditions. Absorption and photoluminescence spectra of CsPbBr 3 quantum dots were tuned from 432 to 521 nm. Upon ultraviolet or blue light excitation, efficient photoluminescence from these CsPbBr 3 quantum dots doped phosphate glasses was observed.

Description: The Static Current Density–Electric Field characteristics of Sr(MnTi) x Fe (12-2x) O 19 ferrite compositions ( x = 0.5, 1.0, 1.5, and 2.0) have been investigated from 4.15 to 36.30 kV/m at room temperature. Ohmic and nonohmic regions are observed at low and high field regimes. The various models, governing nonlinear conduction, are discussed qualitatively in terms of Space charge limited current (SCLC), Ionic hopping, Poole–Frenkel, Schottky–Richardson, and Fowler–Nordheim mechanisms. The results depict Child-Langmuir type SCLC in the investigated compositions.

Description: Disperse fine equiaxed α-Al 2 O 3 nanoparticles with a mean particle size of 9 nm and a narrow size distribution of 2–27 nm were synthesized using α-Fe 2 O 3 as seeds and isolation via homogeneous precipitation-calcination-selective corrosion processing. The presence of α-Fe 2 O 3 acting as seeds and isolation phase can reduce the formation temperature to 700°C and prevent agglomeration and growth of α-Al 2 O 3 nanoparticles, resulting in disperse fine equiaxed α-Al 2 O 3 nanoparticles. These α-Al 2 O 3 nanoparticles were pressed into green compacts at 500 MPa and sintered first by normal sintering to study their sintering behavior and finally by two-step sintering (heated to 1175°C without hold and decreased to 1025°C with a 20 h hold in air) to obtain nanocrystalline α-Al 2 O 3 ceramics. The two-step sintered bodies are nanocrystalline α-Al 2 O 3 with an average grain size of 55 nm and a relative density of 99.6%. The almost fully dense nanocrystalline α-Al 2 O 3 ceramic with finest grains achieved so far by pressureless sintering reveals that these α-Al 2 O 3 nanoparticles have an excellent sintering activity.

Description: This study presents an interesting phenomenon of the simultaneous occurrence of adsorption and synthesis of Mg–Al layered double hydroxide (Mg–Al–LDH) by stirring a precursor in an aqueous solution with methyl orange (MO) as target adsorbate with the precursor prepared by first milling Mg(OH) 2 for 1 h followed by another 3 h milling with Al(OH) 3 .The prepared precursor and LDH samples were characterized by a set of analytical methods including X-ray diffraction (XRD), thermogravimetry/differential scanning calorimetry (TG–DSC), and Fourier-transform infrared (FT–IR). The maximum adsorption capacity ( Q m ) of MO by the prepared precursor sample was 1110.2 mg/g, much higher than that from the synthesized LDH sample. Engineering application may be expected from the easy preparation of such precursor as adsorbent to purify the tremendous amounts of dye wastewater.

Description: The optical quality and microstructure of the Tb 3 Al 2.5 Ga 2.5 O 12 transparent ceramic were investigated and compared with those of Tb 3 Ga 5 O 12 (TGG) and Tb 3 Al 5 O 12 (TAG). The transmission of the Tb 3 Al 2.5 Ga 2.5 O 12 ceramic was as high as 80% in the visible and near-infrared (IR) regions, which was close to the theoretical value. The Verdet constant of the Tb 3 Al 2.5 Ga 2.5 O 12 ceramic measured at 632.8 nm and room temperature was −150.6 rad/Tm, which was 12% larger than that of the TGG single crystal and 13% smaller than that of the TAG single crystal, and the Tb 3 Al 2.5 Ga 2.5 O 12 ceramic showed the highest transparency among these three samples.

Description: A new polymeric boron nitride (BN) precursor poly[(phenylamino)borazine] (PPAB) with good melt-processing performance was successfully synthesized by reaction of B-trichloroborazine (TCB), aniline, and N -methylaniline under mild conditions. The as-synthesized PPAB as well as its structural evolution during the ceramic conversion was studied by means of various complementary techniques. The effect of process parameters including monomer ratio, reaction time, and reaction temperature on the properties of polymers was investigated, and the optimized parameters were obtained. Gel permeation chromatography (GPC) analysis of typical PPAB revealed that the number-average molecular weight ( M n ) was 30,520 Da and the polymerization degree was 319. The polymer could be converted to BN ceramics under ammonia atmosphere at 1200°C with carbon content as low as 0.9wt%. The PPAB polymer could be melt-spun into continuous polymer fibers by hand drawing, which could be further transformed into BN ceramic fibers with good quality. The PPAB polymer is promising for applications that require BN precursor with stable melt processability.

Description: 8% Yttria-stabilized zironcia (8YSZ) transparent ceramics have a wide technological applications. Segregation of the Y around the grain boundaries is favored by slow heating rate. The optimized sintering parameters helped in obtaining transparent ceramics of 8YSZ with a high percentage of cubic phase in addition to the presence of tetragonal phase. HRTEM was used to verify the grain growth suppression and to observe the presence of the cubic phase. The presence of cubic phase has suppressed the grain growth, which increased the transparency in the visible and infrared region without the addition of dopants or by utilizing high pressure.

Description: Mn-doped Ba 0.45 Sr 0.55 TiO 3 ( x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05) ceramics were processed by solid-state route at 1300°C for 6 h in air. Impedance spectroscopic studies showed that the total resistance ( R T ) decreased with the increase in temperature. Samples with x = 0.00, 0.03, and 0.05 exhibited grain boundary contribution to the conduction mechanism. Samples with x = 0.01, 0.02, 0.04 compositions showed both grain (bulk) and grain boundary contributions. Mn substitution proved to be an effective way to optimize the dielectric properties of BST ceramics.

Description: Magnesium is replaced systematically by zinc in Ni 0.2 Mg 0.8- x Zn x Fe 2 O 4 ( x = 0.2–0.8) prepared by microwave-assisted solid-state reaction route. The structure is confirmed by X-ray diffractograms. An improvement in initial permeability is observed with substituent in Ni 0.2 Mg 0.8- x Zn x Fe 2 O 4 due to increase in average grain size. The obtained permeability values are varying between 106 and 687 at 1 MHz. The permeability plots revealed that Curie-transition temperature ( T c ) is decreasing with increase in zinc. Both x = 0.2 and 0.4 compositions show low relative loss factor of order 10 −5 to 10 −4 , which are exhibiting required magnetic properties for transformer and inductor core applications.

Description: The reactivity of BaZrO 3 with CO 2 has been addressed as one of the major challenges with BaZrO 3 -based electrolytes in protonic ceramic fuel cells. Here, we present a study of the effect of CO 2 exposure on BaZrO 3 -materials at elevated temperatures. Dense BaZr 1− x Y x O 3− x /2 ( x = 0, 0.05, 0.1, 0.2) and BaCe 0.2 Zr 0.7 Y 0.1 O 2.95 ceramics were prepared by sintering of powder prepared by spray pyrolysis. The Vickers indentation method was used to determine the hardness and estimate the fracture toughness of pristine materials as well as the corresponding materials exposed to CO 2 . Formation of BaCO 3 on the surface of exposed ceramics was confirmed by X-ray diffraction and electron microcopy. The reaction resulted in formation of Ba-deficient perovskite at the exposed surface. The reaction with CO 2 was most pronounced at 650°C compared to the other temperatures applied in the study. The reactivity was also shown to depend on the Y-content and the grain size and was most pronounced for BaZr 0.9 Y 0.1 O 2.95 . The reaction with CO 2 was observed to have a profound effect on the fracture toughness of the ceramics, demonstrating a depression of the mechanical stability of the materials. The results are discussed with respect to the chemical and mechanical stability of BaZrO 3 materials, with particular emphasis on the composition and grain size.

Description: Single-phase white-light-emitting phosphors NaLa 9(1− x − y ) (GeO 4 ) 6 O 2 : x Tm 3+ , y Dy 3+ (NLGO: x Tm 3+ , y Dy 3+ ) have been synthesized by a traditional solid-state reaction method. The powder X-ray diffraction (XRD), photoluminescence (PL), PL excitation (PLE) spectra, fluorescence decay curves, chromaticity coordinates, correlated color temperature (CCT), and the cathodoluminescence (CL) properties of the obtained phosphors are measured and discussed in detail. It is discovered that the series samples could be color-tunable (from blue to yellow) by tuning the doping content of Dy 3+ with a fixed Tm 3+ content excited at 357 nm and white light (0.341, 0.324) could be obtained with the CCT of 5079 K. A NLGO: 0.01Tm 3+ , 0.02Dy 3+ is studied carefully as representative. The main emissions of Tm 3+ (453 nm, 1 D 2 – 3 F 4 ) and Dy 3+ (478 nm, 4 F 9/2 – 6 H 15/2; 572 nm, 4 F 9/2 – 6 H 13/2 ) make it emit white light with good thermal stability (67% of the initial till 523 K). The energy transfer from Tm 3+ to Dy 3+ is noticed and further research has been done to explain the enhancement of Dy 3+ emission and the excellent thermal stability. It also keeps stable under continuous electron bombardment with high intensity. All of these indicate that it could be a suitable candidate for white-emitting phosphor applied for near ultraviolet-white light-emitting diode (NUV-WLED) and field-emission display (FED).