ALBERT

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: 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: 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: 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: 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: 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: 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: 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 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).

Description: (Pb 0.98 La 0.02 )(Zr 0.45 Sn 0.55 ) 0.995 O 3 antiferroelectric (AFE) thick films with a thickness of about 85 μm were successfully fabricated via a rolling process using an improved sintering method, and all specimens showed high-energy-storage performance. The X-ray diffraction, SEM pictures, and hysteresis loops confirmed that the sintering temperature had an important influence on the microstructures, dielectric properties and energy storage performance of AFE thick films. The grain size and the storage efficiency increased with the increasing sintering temperature, the energy storage performance was enlarged by the rolling process. As a result, a maximum recoverable energy density of 7.09 J/cm 3 with an efficiency of 88% was achieved at room temperature, together with stable energy-storage behavior, which was almost three times higher than that (2.43 J/cm 3 ) of the bulk ceramics counterparts. The results demonstrated that the improved method was an effective way to improve the breakdown strength and energy storage performance of AFE thick films, and (Pb 0.98 La 0.02 )(Zr 0.45 Sn 0.55 ) 0.995 O 3 AFE thick films were a promising material for high-power energy storage.

Description: For the study of negative thermal expansion (NTE) compounds, it is critical to effectively control the thermal expansion. In this letter, a chemical approach has been taken to control the thermal expansion behavior in ScF 3 which has a strong NTE. Owing to the difference of radius of substituting ions, local distortion inevitably emerges in the lattice matrix, which is verified by pair distribution function analysis of high-resolution synchrotron X-ray scattering. It is a valuable clue that the thermal expansion behaviors in the ScF 3 based systems and other trifluorides are correlated closely to structural distortion of metal-F-metal linkages. In addition, the introduction of 3 d transition-metal enables its semiconductor and ferromagnetic characteristics. This study provides important reference opinion for the control of thermal expansion and introduction of multifunctionalization for those NTE compounds with open framework structure.

Description: Rare-earth-doped oxyfluoride germanate and borate glasses were synthesized and next studied using spectroscopic methods. Influence of fluoride modifier on luminescence properties of rare earths in different glass hosts was examined. The excitation and emission spectra of Pr 3+ and Er 3+ ions in the studied glasses were registered. The emission spectra of Pr 3+ ions in germanate and borate glasses are quite different and depend strongly on the glass host. In samples doped with Er 3+ ions emission bands located around 1530 nm corresponding to the main 4 I 13/2 4 I 15/2 laser transition were registered, independently of the glass host. Quite long-lived near-infrared luminescence of Er 3+ ions was observed for germanate glasses with low BaF 2 content, while in borate glass systems influence of barium fluoride on luminescence lifetimes is not so evident. The Judd–Ofelt calculations were used in order to determine quantum efficiencies of excited states of rare-earth ions in germanate and borate glasses.

Description: Herein, we report—for the first time—on the additive-free bulk synthesis of Ti 3 SnC 2 . A detailed experimental study of the structure of the latter together with a secondary phase, Ti 2 SnC, is presented through the use of X-ray diffraction (XRD), and high-resolution transmission microscopy (HRTEM). A previous sample of Ti 3 SnC 2 , made using Fe as an additive and Ti 2 SnC as a secondary phase, was studied by high-temperature neutron diffraction (HTND) and XRD. The room-temperature crystallographic parameters of the two MAX phases in the two samples are quite similar. Based on Rietveld analysis of the HTND data, the average linear thermal expansion coefficients of Ti 3 SnC 2 in the a and c directions were found to be 8.5 (2)·10 −6 K −1 and 8.9 (1)·10 −6 K −1 , respectively. The respective values for the Ti 2 SnC phase are 10.1 (3)·10 −6 K −1 and 10.8 (6)·10 −6 K −1 . Unlike other MAX phases, the atomic displacement parameters of the Sn atoms in Ti 3 SnC 2 are comparable to those of the Ti and C atoms. When the predictions of the atomic displacement parameters obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Sn atoms. In the case of the Ti and C atoms, the agreement is more qualitative. We also used first principles to calculate the elastic properties of both Ti 2 SnC and Ti 3 SnC 2 and their Raman active modes. The latter are compared to experiment and the agreement was found to be good.

Description: The oxidation behavior of ZrB 2 –SiC-graphite composites under low oxygen partial pressures of 500 and 1500 Pa at 1800°C was investigated. The phase composition and microstructure of the oxidized scale were characterized using TEM, SEM, XRD, XPS, EDS. The analytical results indicated that a low oxygen partial pressure had a remarkable effect on the oxidation mechanism of ZrB 2 –SiC-graphite composites. When oxidized at 1500 Pa, the oxidation kinetics was controlled by the rate of oxygen diffusion into the composite. When the composite was oxidized at 500 Pa, control of the oxidation kinetics changed from the rate of oxygen diffusion to the rate of the oxidation reaction. The rate of oxidation decreased with decreasing oxygen partial pressure. Higher partial pressures of oxygen resulted in less oxidation resistance by the ZrB 2 –SiC-graphite composites.

Description: [(K 0.43 Na 0.57 ) 0.94 Li 0.06 ][(Nb 0.94 Sb 0.06 ) 0.95 Ta 0.05 ]O 3 + x mol% Fe 2 O 3 (KNLNST + x Fe, x = 0~0.60) lead-free piezoelectric ceramics were prepared by conventional solid-state reaction processing. The effects of small-amount Fe 2 O 3 doping on the microstructure and electrical properties of the KNLNST ceramics were systematically investigated. With increasing Fe 3+ content, the orthorhombic-tetragonal polymorphic phase transition temperature ( T O-T ) of KNLNST + x Fe ceramics presented an obvious “V” type variation trend, and T O-T was successfully shifted to near room temperature without changing T C ( T C = 315°C) via doping Fe 2 O 3 around 0.25 mol%. Electrical properties were significantly enhanced due to the coexistence of both orthorhombic and tetragonal ferroelectric phases at room temperature. The ceramics doped with 0.20 mol% Fe 2 O 3 possessed optimal piezoelectric and dielectric properties of d 33 = 306 pC/N, k p = 47.0%, = 1483 and tan δ = 0.023. It was revealed that the strong internal stress in the KNLNST + x Fe ceramics with higher Fe 3+ contents ( x = 0.40, 0.60) stabilized the orthorhombic phase, leading to the irregular “V” type rather than the usually observed monotonic phase transition with composition change in the ceramics.

Description: Versatile and intriguing solution-based processes are utilized to synthesize nanostructured materials for device applications to reduce material production and device fabrication costs. This study presents results on the fabrication and characterization of copper oxide (CuO) coated cobalt-doped zinc oxide nanowires (Co-doped ZnO NWs)-based heterojunction diodes prepared by a two-step synthesis route through combined hydrothermal growth and sol–gel spin coating. Highly dense, well-ordered, undoped, and Co-doped ZnO NWs were successfully grown by hydrothermal method. Complementary CuO thin films were synthesized by sol–gel method and subsequently coated onto both undoped and Co-doped ZnO NWs through spin-coating technique. Enhanced diode properties with a rectification ratio of 10 3 at ±2 V and an ideality factor of n = 2.4 (in dark) were obtained for Co-doped ZnO NWs-based heterojunction diodes. The obtained results demonstrated that the investigated heterojunction diode structure fabricated by facile and cost-effective solution-based processes can be a promising candidate for the next generation optoelectronic devices.

Description: Y–Si–O–N quaternary oxynitrides (Y 5 Si 3 O 12 N, Y 4 Si 2 O 7 N 2 , YSiO 2 N, Y 2 Si 3 O 3 N 4 , and Y 3 Si 5 ON 9 ) are recognized as important secondary grain-boundary phases in silicon nitride and believed to have important impacts on the high-temperature mechanical properties and thermal conductivity of Si 3 N 4 ceramic. In this work, equilibrium crystal structures, theoretical mechanical properties (second-order elastic constants, polycrystalline bulk modulus , shear modulus , Young's modulus, and Vickers hardness) of the five quaternary phases are calculated using first-principle total energy calculations. Meanwhile, temperature dependence of thermal conductivities of all five compounds is obtained based on Debye–Clarke model and Slack equation. On the basis of theoretical prediction, we establish the relationship between the componential (cation/anion or cation/cation ratios) and structural characteristics (bonding configurations) and mechanical/thermal properties. Our results are expected to provide helpful guidelines to improve the performances of Y–Si–O–N ceramics, and further guide the optimization of mechanical and thermal properties of Si 3 N 4 by properly tailoring the secondary grain-boundary phases.

Description: By conventional ceramics sintering technique, the lead-free 0.85Bi 0.5 Na 0.5(1− x ) Li 0.5 x TiO 3 -0.11Bi 0.5 K 0.5 TiO 3 -0.04BaTiO 3 ( x =0–0.15) piezoelectric ceramics were obtained and the effects of Li dopant on the piezoelectric, dielectric, and ferroelectric properties were studied. With increasing Li addition, the temperature-dependent permittivity exhibited the normal ferroelectric-to-ergodic relaxor (FE-to-ER) transition temperature ( T FE - ER , abbreviated as T F-R ) decreasing down to room temperature. The increasing Li content also enhanced the diffuseness of the FE-to-ER transition behavior. For composition with x = 0.15, a large unipolar strain of 0.37% ( = S max / E max = 570 pm/V) was achieved under 6.5 kV/mm applied electric field at room temperature. Both unipolar and bipolar strain curves related to the temperature closely, and when the temperature reached the T F-R , the normalized strain achieved a maximum value (e.g., for x = 0.10, = 755 pm/V) owing to the electric-field-induced ER-to-FE state transition.

Description: Mn-doped (Bi 0.5 Na 0.5 ) 0.94 Ba 0.06 TiO 3 (MnBNBT) thin films were prepared on SrRuO 3 (SRO)-coated (001) SrTiO 3 (STO) single crystal substrates by pulsed laser deposition under different processing conditions. Structural characterization (i.e., XRD and TEM) confirms the epitaxial growth of STO/SRO/MnBNBT heterostructures. Through the judicious control of deposition temperature, the defect level within the films can be finely tuned. The MnBNBT thin film deposited at the optimized temperature exhibits superior ferroelectric and piezoelectric responses with remanent polarization P r of 33.0 μC/cm 2 and piezoelectric coefficient d 33 of 120.0 ± 20 pm/V.

Description: The short and medium range structure of glassy MoO 3 –ZnO–B 2 O 3 has been studied by neutron diffraction and reverse Monte Carlo simulation. The partial atomic pair correlation functions and coordination numbers are presented that are not yet reported for this system. We have established that the first neighbor distances do not depend on concentration within limit of error, the actual values are r B-O = 1.38 Å, r Mo-O = 1.72 Å, and r Zn-O = 1.97 Å. It is found that ZnO takes part in the glassy structure as network former, as ZnO 4 tetrahedral are linked both to MoO 4 and to BO 3 and BO 4 groups. It is revealed that BO 4 /BO 3 increases with increasing B 2 O 3 content. We have found that only small amount of boroxol ring is present, BO 3 and BO 4 groups are organized into superstructure units, and a small part is in isolated BO 3 triangles. The BO 3 and BO 4 units are linked to MoO 4 or ZnO 4 forming mixed [4] Mo-O- [3] B, [4] Mo-O- [4] B, [4] Mo-O- [4] Zn, [3] B-O- [4] Zn, [4] B-O- [4] Zn bond linkages.

Description: This work reports on process-induced impurities in rare-earth ion: Dy 3+ -doped selenide chalcogenide glasses, which are significant materials for active photonic devices in the mid-infrared region. In particular, the effect of contamination from the silica glass ampoule containment used in chalcogenide glass synthesis is studied. Heat-treating Dy-foil-only, and DyCl 3 -only, separately, within evacuated silica glass ampoules gives direct evidence of silica ampoule corrosion by the rare-earth additives. The presence of [Ga 2 Se 3 ] associated with [Dy] on the silica glass ampoule that has been contact with the chalcogenide glass during glass melting, is reported for the first time. Studies of 0–3000 ppmw Dy 3+ -doped Ge 16.5 As 9 Ga 10 Se 64.5 glasses show that Dy-foil is better than DyCl 3 as the Dy 3+ additive in Ge-As-Ga-Se glass in aspects of avoiding bulk crystallization, improving glass surface quality and lowering optical loss. However, some limited Dy/Si/O related contamination is observed on the surfaces of Dy-foil-doped chalcogenide glasses, as found for DyCl 3 -doped chalcogenide glasses, reported in our previous work. The surface contamination indicates the production of Dy 2 O 3 and/or [≡Si-O-Dy=]-containing particles during chalcogenide glass melting, which are potential light-scattering centers in chalcogenide bulk glass and heterogeneous nucleation agents for α-Ga 2 Se 3 crystals.

Description: New strategies for fabricating multiphase bioceramic porous scaffolds with time-dependent biodegradation and pore network enlargement are of fundamental importance in the advancement of bioceramics. Here, we developed a one-step preparation of core–shell bioceramic microspheres (~2 mm in diameter) with single- or double-shell structure through a coaxially aligned multilayer capillary system. The Ca-phosphate (CaP) and Ca-silicate (CaSi) ceramic phase distribution could be also adjusted by extruding through different capillaries, and thus the biodegradation rate would be readily tailored over time. When the polystyrene (PS) microbeads of ~15 μm in diameter were premixed into the CaP- or CaSi-containing alginate slurry, the tailorable porous structures could be introduced into the core or different shell layers of the microspheres. These micropores may potentially maximize the permeability for rapid exchange of guest molecules or inorganic ions from the bioceramics. Totally, such strategy is promising because the ceramic phases with different biological properties can be assembled into the core–shell bioceramic microspheres, and thus the macropore structure evolution may be readily manipulated in the closely packed microsphere systems. We believe our gradient hybrid methodology will have potential in various categories of advanced biomaterials of organic–inorganic composites.

Description: All-oxide composites are increasingly investigated in the field of microelectronics and telecommunications because of their multifunctionalities. Advanced control of interfaces is required to fully tune the macroscopic properties of the composites. Processing ferroelectric Ba 0.65 Sr 0.35 TiO 3 (BST65/35)-TiO 2 composites by Spark Plasma Sintering (SPS), we show that the SPS electric current promotes an interphase growth whose thickness depends on the BST/ TiO 2 stacking and on the current direction. In all cases, the interface is composed of Ba 1.14(2) Ti 8 O 16-δ a highly defective, but stable phase which can be used to tune the overall dielectric properties of the composites.

Description: Synthesis of CeO 2 , Pr 2 O 3 , and Sm 2 O 3 nanorods and their sintering have been investigated. In a strongly alkaline medium, nanorods of CeO 2 , Pr 2 O 3 , and Sm 2 O 3 were prepared from trivalent salts of rare earths (Ce, Pr, Sm) via precipitation synthesis. Nanorods were formed by nanocrystallites of fibrous structure, which were produced by the mechanism of self-arrangement of hexagonal particles of Re(III) hydroxides. The subsequent transformation of hydroxide into oxide proceeded via self-preservation of the rod-like structure. In CeO 2 , the fibrous structure was noncohesive during thermal treatment at temperature of 500°C and higher. Regardless of the shape of the CeO 2 particles (spherical versus rod-like), sintered ceramic was formed by equiaxial grains. The cohesion of the fibrous structure of Pr and Sm oxides was higher than in CeO 2 . The rod-like shape of the particles of Pr and Sm oxides was (partially) preserved during sintering.

Description: Polycrystalline SmBaCuFeO 5+δ /Ag composite ceramics have been synthesized by a traditional ceramic processing method. Phase composition and microstructural analyses indicate that with the introduction of Ag additives, the second phases of copper oxides and Ag appear in these composite ceramic samples. The hole concentration and molibility can be enhanced greatly by the addition of Ag particles, which results in a large increase in the electrical conductivity. The thermal conductivity behaviors show that phonons can be scattered effectively by point defects and mesoscale grain boundaries, which remain a slight change in thermal conductivity. A maximum ZT value 0.047 has been achieved at 1023 K in the SmBaCuFeO 5+δ /20 vol% Ag composite ceramic, and is about 16 times than the pure SmBaCuFeO 5+δ sample. Our results reveal that Ag addition is an effective way to enhance the thermoelectric properties.

Description: This paper presents an inverse method for retrieving (i) the true thermal conductivity, and (ii) the two-band absorption coefficient of soda-lime silicate glassmelts between 1100°C and 1550°C from measured steady-state temperature profiles. This was achieved by combining (i) a forward method solving combined conductive and radiative heat transfer accounting for temperature-dependent thermal conductivity and spectral absorption coefficient and (ii) an inverse method based on genetic algorithm (GA) optimization. Four glassmelt compositions from ultraclear to gray glasses with iron content ranging from 0.008 to 1.1 wt% were investigated. First, it was established that the steady-state temperature in glassmelt can be predicted accurately by averaging the spectral absorption coefficient over two bands from 0 to 2.8 μm and 2.8 to 5.0 μm. The inverse method showed that the true thermal conductivity was independent of the iron content and given by k c ( T ) = 1.31 + 5.90 × 10 −4 T , where T is given in °C. In addition, the band absorption coefficient between 0 and 2.8 μm strongly increased with increasing iron content, while the band absorption coefficient between 2.8–5.0 μm was independent of iron content.

Description: A detailed study of a novel synthesis via colloidal sol–gel route for obtaining nanoparticulate Nb 2 O 5 was performed. Parameters such as temperature and H + :Nb 5+ and Nb 5+ :H 2 O molar ratios were controlled in order to determine the best conditions of synthesis. Moreover, particle size distribution, zeta potential, structure by X-ray diffraction, and the photocatalytic activity of the particulate sols were also evaluated. The obtained results indicate that the colloidal sol–gel synthesis is a good alternative for obtaining Nb 2 O 5 either as stable nanoparticulate sol or as a nanosized powder. Nb 2 O 5 amorphous nanoparticles with an average size of 20 nm were obtained by controlling the synthesis variables. The heat-treatment process allowed the formation of Nb 2 O 5 with orthorhombic structure that transforms at higher temperatures to monoclinic phase. The highest photocatalytic activity was observed under λ = 365 nm, the smallest UV energy used in the experimental tests.

Description: Glass optics with ultra-low roughness surfaces (〈2 Å rms) are strongly desired for high-end optical applications (e.g., lasers, spectroscopy, etc.). The complex microscopic interactions that occur between slurry particles and the glass workpiece during optical polishing ultimately determine the removal rate and resulting surface roughness of the workpiece. In this study, a comprehensive set of 100 mm diameter glass samples (fused silica, phosphate, and borosilicate) were polished using various slurry particle size distributions (PSD), slurry concentrations, and pad treatments. The removal rate and surface roughness of the glasses were characterized using white light interferometry and atomic force microscopy. The material removal mechanism for a given slurry particle is proposed to occur via nano-plastic deformation (plastic removal) or via chemical reaction (molecular removal) depending on the slurry particle load on the glass surface. Using an expanded Hertzian contact model, called the Ensemble Hertzian Multi-gap (EHMG) model, a platform has been developed to understand the microscopic interface interactions and to predict trends of the removal rate and surface roughness for a variety of polishing parameters. The EHMG model is based on multiple Hertzian contacts of slurry particles at the workpiece–pad interface in which the pad deflection and the effective interface gap at each pad asperity height are determined. Using this, the interface contact area and each particle's penetration, load, and contact zone are determined which are used to calculate the material removal rate and simulate the surface roughness. Each of the key polishing variables investigated is shown to affect the material removal rate, whose changes are dominated by very different microscopic interactions. Slurry PSD impacts the load per particle distribution and the fraction of particles removing material by plastic removal. The slurry concentration impacts the areal number density of particles and fraction of load on particles versus pad. The pad topography impacts the fraction of pad area making contact with the workpiece. The glass composition predominantly impacts the depth of plastic removal. Also, the results show that the dominant factor controlling surface roughness is the slurry PSD followed by the glass material's removal function and the pad topography. The model compares well with the experimental data over a variety of polishing conditions for both removal rate and roughness and can be extended to provide insights and strategies to develop practical, economic processes for obtaining ultra-low roughness surfaces while simultaneously maintaining high material removal rates.

Description: A high-hardness diamond-based composite was synthesized by spark plasma sintering (SPS) under 100 MPa, using SiC-coated diamond powder prepared via chemical vapor deposition (CVD). SiC layers 20–40 nm were uniformly deposited on diamond powders by a rotary CVD technique. The SiC-coated diamond powder was consolidated with SiO powder by SPS at the sintering temperature of 1873 K, resulting in the formation of fully compacted mosaic microstructure with the Vickers hardness of 36 GPa.

Description: Solid solutions of (1− x )BaTiO 3 – x Bi(Mg 2/3 Nb 1/3 )O 3 (0 ≤ x ≤ 0.6) were prepared via a standard mixed-oxide solid-state sintering route and investigated for potential use in high-temperature capacitor applications. Samples with 0.4 ≤ x ≤ 0.6 showed a temperature independent plateau in permittivity (ε r ). Optimum properties were obtained for x = 0.5 which exhibited a broad and stable relative ε r ~940 ± 15% from ~25°C to 550°C with a loss tangent 〈0.025 from 74°C to 455°C. The resistivity of samples increased with increasing Bi(Mg 2/3 Nb 1/3 )O 3 concentration. The activation energies of the bulk were observed to increase from 1.18 to 2.25 eV with an increase in x from 0 to 0.6. These ceramics exhibited excellent temperature stable dielectric properties and are promising candidates for high-temperature multilayer ceramic capacitors for automotive applications.

Description: The direct ink writing of an ink composed of a preceramic polymer and fillers was used to produce hardystonite (Ca 2 ZnSi 2 O 7 ) bioceramic scaffolds. Suitable formulations were developed for the extrusion of fine filaments (350 μm diameter) through a nozzle. The preceramic polymer was employed with the double purpose of contributing to the rheology of the ink by increasing its viscosity and of forming the hardystonite phase upon heat treatment by reacting with the fillers. A control of the rheology is essential when spanning features have to be produced, and therefore the main rheological characteristics of the inks were measured (flow curves, dynamic oscillation tests, viscosity recovery tests) and compared to models reported in the literature. Highly porous scaffolds (up to 80% total porosity) were produced and heat treated in air or in nitrogen atmosphere. The influence of the heat-treatment atmosphere on the morphology, crystalline phase assemblage, and compressive strength of the scaffolds was investigated.

Description: The poling effect on the [011]-oriented (1− x )Pb(Mg 1/3 Nb 2/3 )O 3 - x PbTiO 3 (PMN– x PT) single crystals across the morphotropic phase boundary (MPB) was studied. The dielectric and piezoelectric properties were investigated as a function of the poling field. Domain structure evolutions during the poling process were recorded. In the unpoled PMN– x PT phase diagram, an apparent rhombohedral (R)-tetragonal (T) phase boundary exists. With room-temperature poling, the structure transformation sequence strongly depends on the composition. The crystal experiences a direct transition to the 2R/2T domain state in the rhombohedral or tetragonal phase field beyond the MPB region, whereas within the MPB zone it is hard to achieve the 2R/2T engineered configuration although the initial state is either rhombohedral or tetragonal as well. The piezoelectric responses of the MPB·PMN– x PTs are extraordinary weak ( d 33 ~ 250 pC/N), in contrast to the [011]-oriented multidomain PMN– x PTs with ultrahigh-piezoelectric coefficient ( d 33 〉 1000 pC/N). We demonstrate that a slight composition variation near the MPB will significantly influence the domain evolution route and piezoelectricity for the [011]-oriented PMN– x PT crystals. We also confirm the feasibility to realize the 2R/2T engineered domain configuration for the [011]-oriented MPB crystals, which will extend the desired portion of the Bridgeman-grown boules with optimal piezoelectric properties.

Description: The present paper deals with the synthesis of porous, sintered glass-ceramics obtained at temperatures below 1150°C, originating from inorganic polymers based on fayalite slag. Firing led to the evaporation of water, dehydroxylation, and oxidation of Fe 2+ above 345°C. For heating 〉700°C, the Si–O stretching band shifted from the 1160 and 750 cm −1 to the 1255 and 830 cm −1 region, due to a structural reorganization of the amorphous phase, whereas Fe–O bands appeared at 550 cm −1 . The final microstructure consisted predominantly of an amorphous phase, hematite, and franklinite. The open porosity and compressive strength decreased and increased, respectively, as the firing temperature increased. The final values suggest properties comparable to that of structural lightweight concrete, still, the materials synthesized herein, are lighter, and made primarily from secondary resources.

Description: A novel low-temperature sintering microwave dielectric based on forsterite (Mg 2 SiO 4 ) ceramics was synthesized through the solid-state reaction method. The effects of LiF additions on the sinterability, phase composition, microstructure, and microwave dielectric properties of Mg 2 SiO 4 were investigated. It demonstrated that LiF could significantly broaden the processing window (~300°C) for Mg 2 SiO 4 , and more importantly the sintering temperature could be lowered below 900°C, maintaining excellent microwave dielectric properties simultaneously. The 2 wt% LiF-doped samples could be well-sintered at 800°C and possessed a ε r ~ 6.81, a high Q×f ~ 167 000 GHz, and a τ f ~ −47.9 ppm/°C, having a very good potential for LTCC integration applications.

Description: The development of barium strontium titanate-based tunable dielectrics is currently hindered by high losses in the paraelectric phase. Barium strontium titanate (BST) thin films and ceramics show a range of ferroelectric transition behavior, from normal, diffuse, and relaxor-like ferroelectric responses, depending on the sample preparation route. Rayleigh analysis, the temperature-dependent dielectric response, and the optical second harmonic generation were used to characterize the ferroelectric response of bulk and thin film BST. Ferroelectricity is observed to persist in BST for 30°C above the global phase transition temperature in ceramics and over 50°C in thin films. Piezoresponse force microscopy on BST ceramics with extensive residual ferroelectricity reveals the coexistence of nanoscale polar regions, typical of relaxor ferroelectrics, as well as micrometer scale domain structures. The nature of the phase transition was probed using electron energy loss spectroscopy and found to correlated with the nanoscale A-site chemical inhomogeneity in the samples.

Description: Single-phase multiferroic Ba(Fe 0.67 Ce 0.33 ) 0.01 Ti 0.99 O 3 (BFTO:Ce) and Ba(Fe 0.67 La 0.33 ) 0.01 Ti 0.99 O 3 (BFTO:La) nanostructures were synthesized by a hydrothermal method (180°C/48 h). Rietveld refinement of X-ray diffraction could confirm crystalline phase and lattice deformation by Ce, La into BFTO. The Ce and La doping induce nanoaggregation-type BFTO nanostructural product due to their ionic size effect and chemical behavior with OH − ions. Raman active modes show tetragonal phase and defects due to vacancies in the BFTO lattice. Photoluminescence spectrum involves multiple visible emissions due to defects/vacancies. The observed ferroelectric polarization is enhanced due to shape/size effect of nanoparticles, lattice distortion, and filling of d orbital in the perovskite BaTiO 3 . The room-temperature magnetic behavior is described due to antiferromagnetic interactions that strengthen by Ce and La doping. The zero-field cooling and field cooling magnetic measurement at 500 Oe indicates antiferromagnetic to ferromagnetic transition. Dynamic magnetoelectric coupling was investigated, and maximum longitudinal magnetoelectric coefficient is 62.65 and 49.79 mV/cmOe, respectively, measured for BFTO:Ce and BFTO:La. The magnetocapacitance measurements induce negative values that described in terms of magnetoresistance and magnetic phase transition effects. The influence of oxygen vacancy on multiferroicity is evaluated by valance states of O ions.

Description: Lead-free binary K 1/2 Bi 1/2 TiO 3 -Bi(Mg 1/2 Ti 1/2 )O 3 (KBT-BMT) ferroelectric ceramics with a morphology of dense and evenly sized grains have been prepared by conventional solid oxide reaction route. X-ray diffraction analysis indicates that all the samples possess pure perovskite structure, and undergo a phase transformation from tetragonal to pseudocubic phase as BMT adds into KBT. Meanwhile, BMT addition brings in the enhancement of the relaxor behavior as revealed by temperature-dependent dielectric profiles and the P–E loops. The impedance analysis reveals that the relaxation process existing in the ceramics belongs to a localized species. Further, in the frequency-dependent M ″ (f) spectra, a shoulder response emerges accompanied by a bulk response as suitable amount of BMT is added, and its frequency dependence obeys Vogel–Fulcher relation f = f 0 exp[ - E b / k B ( T - T VF )]. The shoulder response is believed to be the evidence of the existence of the polar nanoregions, which dominate the relaxor behavior of KBT-BMT ceramics.

Description: Ceramics 0.94(K 0.5 Na 0.5 )NbO 3 −0.06LiNbO 3 :Er/ x Yb with x = 0, 0.002, 0.004, 0.006, 0.008 were fabricated in this study, and phase structure, dielectric, piezoelectric, ferroelectric, and upconversion photoluminescence properties of the ceramics were systematically studied. Results show that all ceramics are in the polymorphic phase transition region near room temperature. However, a relaxor-like phase transition was observed as Yb increasing to over x = 0.004. The optimized dielectric, piezoelectric, and ferroelectric properties, and maximized photoluminescence intensity ratio are obtained at x = 0.004. And the electrical and photoluminescence properties of the ceramics were discussed from the point view of the normal to relaxor-like ferroelectric phase transition. The present study demonstrates that both the electrical and upconversion photoluminescence properties of the ceramics have an intimate correlation with the normal to relaxor-like ferroelectric transition induced by Yb doping.

Description: In this article, Al -doped ZnO thin films deposited by a one single-layer approach are studied. An aqueous precursor solution was prepared for the deposition of Al -doped ZnO thin film via ink-jet printing. The physical properties of the ink were studied in detail by rheology measurement and drop visualization. The wetting of the ink with the substrate was studied by the use of wetting envelopes. A single layer of the ink was deposited on the substrate and fully processed. The thin films were studied by X-ray diffraction, scanning electron microscopy, resistivity measurements, and optical transmission measurements. The optimal dopant concentration was set at 3 at.%, which resulted in thin films with a resistivity of 2.54 cΩ cm and an optical transmission larger than 90% over the visible range of the electromagnetic spectrum.

Description: Sodium bismuth titanate (Na 0.5 Bi 0.5 TiO 3 , NBT) crystals with different morphology, wires, plates and cubes, were synthesized by hydrothermal method. The domain structure in as-synthesized poled NBT ceramics was observed. The results demonstrate that the domain width of the poled NBT ceramics sintered from wire crystals is slightly larger than that of the NBT ceramics sintered from cube crystals, while the NBT ceramics sintered from plate crystals possess the largest domain width. In particular, the poled NBT ceramics sintered from plate crystals exhibit the optimum piezoelectric coefficient and remnant polarization of 87 pC/N and 36.7 μC/cm 2 , respectively, which are 55% and 37% higher than those of the NBT ceramics sintered from cube crystals. The expanded domain width and large grain size are responsible for the improvement of ferroelectric, piezoelectric, and dielectric properties in NBT ceramics.

Description: Rapid repair concrete mixtures commonly used for full-depth concrete pavement repair sections can use large dosages of accelerating admixtures to increase strength gain rates and decrease the time to traffic opening. Most often, these mixtures also contain water-reducing and retarding admixtures (WRRAs) to allow for the use of a low water–cementitious material ratio in order to meet strength requirements. The use of large dosages of accelerating admixtures in combination with retarding admixtures could have significant side effects on concrete. Autogenous shrinkage of low water–cementitious concrete can contribute to high tensile stresses and cracking problems. The effect of calcium chloride-based accelerating admixture dosage, when used with WRRAs, on autogenous shrinkage was measured. It was found that the inclusion of calcium chloride-containing accelerating admixtures has a nonlinear effect on the pore size distribution and consequently a nonlinear increase on the autogenous shrinkage.

Description: This paper reports a new strainless fabrication method for ytterbium-doped CaF 2 laser ceramics involving no drying step before green body casting. The nanoparticles were kept in aqueous solution until green body shaping. Centrifugation was used to obtain correct compactness of the green body before sintering. Characterizations were conducted at different steps of the fabrication process. No grain boundaries oxidation was observed in the sintered ceramics although the nanoparticles were permanently maintained in water until they were sintered. Finally, these ceramics are more homogeneous and have less light scattering defects (no porosity), and present improved optical properties when compared to ceramics obtained from dried nanopowders.

Description: Single-phase monoclinic aluminum–gallium oxide powders, β−(Al x Ga 1− x ) 2 O 3 , have been produced by solution combustion synthesis for Al fraction 0 ≤  x  〈 0.8. α−(Al x Ga 1− x ) 2 O 3 is observed for x  = 1, with mixed α + β for x  = 0.8. The contraction in lattice parameters and increase in band gap with increasing Al concentration were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively, and are compared with a first-principles density-functional theory calculation. A novel filtering procedure is described to reduce the uncertainty involved in measuring band gap using photoemission, and to remove asymmetry in XPS line shapes caused by differential charging of loose powder. The lattice parameters vary linearly with Al fraction, but exhibit a change in slope at x  = 0.5 that is attributed to the difference between aluminum occupying tetrahedral and octahedral sites in the monoclinic lattice. The band gap changes linearly with local stoichiometry, including increasing when aluminum content at the surface is enriched relative to the interior, with a range of over 1.8 eV.

Description: The electrical properties of polycrystalline NiZn ferrite, Zn 0.44 Ni 0.38 Fe 2.18 O 4 , were investigated by impedance spectroscopy over the frequency and temperature ranges, 5 Hz to 2 MHz and 10–600 K and by magnetic permeability measurements at room temperature. Samples were sintered in either conventional or solar furnaces followed by quenching or slow cooling to ambient temperature. Depending on processing conditions, the room-temperature electrical resistivity of conventionally sintered samples varied by seven orders of magnitude, from 5 ohm cm for a sample quenched from 1250°C to 10 Mohm cm for a sample quenched from 400°C. These differences were attributed to variations in oxygen content of the ferrite which decreased with increasing quench temperature. Oxygen deficiency led to mixed valence of Fe in the octahedral B sites of the spinel structure and was responsible for high electronic conductivity with low activation energy at low temperatures in oxygen-deficient samples. By contrast, in oxygen-stoichiometric samples, Fe on the tetrahedral A sites was believed to be divalent and Fe on the octahedral B sites to be entirely trivalent. Electron hopping between A and B sites had much higher activation energy and dominated the conductivity at high temperature for all samples. Samples sintered in the solar furnace were much more conductive than ones that were slow-cooled after conventional sintering and this is attributed to the relatively rapid cooling rate after exposure in the solar furnace, which preserved some of the oxygen deficiency present at high temperature. For the same reason, samples that were slow cooled in N 2 were also much more conductive. Solar-sintered samples with higher density (96%) had higher real permeability than slow-cooled, conventionally sintered ones (86%) mainly due to a combination of their lower resistivity and higher density. Resistivity seems to have a greater correlation with the imaginary permeability than density has.

Description: Reaction sintering of sodium carbaboride (NaB 5 C) was performed by heating compacts of mixtures of amorphous boron (B) and carbon black (C) powders (B/C molar ratio, 5/1) at 1173 K in Na vapor. The ceramics obtained from the compacts of B 5 /C powder mixed with a ball mill (compact density, 1.67 Mg/m 3 ) were the composites of NaB 5 C (74 mass%) and unreacted B 5 /C (26 mass%). The bulk density and bending strength of the composite ceramics were 2.04 ± 0.03 Mg/m 3 and 320.9 ± 10.4 MPa, respectively. Transmission electron microscope observation revealed that nanometer-size amorphous grains of B or C were included in the matrix of NaB 5 C.

Description: Bi 3.15 Nd 0.85 Ti 3 O 12 (BNdT)/CoFe 2 O 4 (CFO) composite ceramic powders with embedded structures were successfully prepared by sol–gel processing. Their crystallization behavior was characterized by XRD, DTA, FT-IR, and HRTEM. The magnetic and ferroelectric phases of these composite ceramic powders segregate during calcination. The CFO phase forms easily at ~300°C, thereafter the BNdT matrix phase nucleates with grain growth at the CFO grain boundaries at temperatures 〉500°C. The CFO phase acts as a heterogeneous nucleation point for formation of the ferroelectric BNdT phase. Furthermore, the 0.5BNdT–0.5CFO composite ceramic powders go through a ferroelectric–paraelectric phase transition at 259°C, and the magnetic CFO nanoparticles (50–100 nm, under calcination at 600°C) embedded in the ferroelectric matrix, show superior magnetic behavior ( M max = 16.50 emu/g), comparable to pure CFO nanoparticles.

Description: The in situ synthesis/consolidation of B 4 C–TaB 2 eutectic composites by spark plasma sintering (SPS) is reported. Samples for the evaluation of bending strength were cut from specimens with diameters of 30 mm. The sample prepared for the three-point flexural strength test had fibers of tantalum diboride with diameter of 1.3 ± 0.4 μm distributed in the B 4 C matrix, thereby reducing composites brittleness and yielding an indentation fracture toughness of up to 4.5 MPa·m 1/2 . Furthermore, the Vickers hardness of B 4 C–TaB 2 eutectics formed by SPS was as high as 26 GPa at an indentation load of 9.8 N. The flexural strength of the B 4 C–TaB 2 system has been reported for the first time. Some steps were identified in the load–displacement curve, suggesting that micro- and macrocracking occurred during the flexural test. Ceramic composites with a eutectic structure exhibited a room-temperature strength of 430 ± 25 MPa. Compared with other eutectic composites of boron carbide with transition-metal diborides, room-temperature strength the B 4 C–TaB 2 was 40% higher than that of B 4 C–TiB 2 ceramics, demonstrating advantage of the in situ synthesis/consolidation of eutectic composites by SPS.

Description: Systematic microstructural statistics for 3 mol% yttria-stabilized zirconia synthesized by both conventional sintering and flash sintering with AC and DC current were obtained. Within the gage section, flash sintered microstructures were indistinguishable from those synthesized by conventional sintering procedures. With both techniques, full densification was obtained. However, from both AC and DC flash sintered specimens, heterogeneous grain size distributions and residual porosity were observed in the proximity of the electrodes. After DC sintering, an almost 400 times increased average grain size was observed near cathode compared to the gage section, unlike areas close to the anode. Concepts of Joule heating alone were not sufficient to explain the experimental observations. Instead, the activation energy for grain growth close to the cathode is lowered considerably during flash sintering, hence suggesting that electrode effects can cause significant heterogeneities in microstructure evolution during flash sintering. Microstructural characterization further indicated that microfracturing during green-pressing and variations in contact resistance between the electrodes and the ceramic may also contribute to grain size gradients and hence local variations of physical properties.

Description: (Na 1− x K x )NbO 3 (NKN) platelets synthesized at 600°C for 12 h have an Amm 2 orthorhombic structure. However, the structure of NKN platelets synthesized at 500°C is a mixture of R 3 m rhombohedral and Amm 2 orthorhombic structures. The formation of a rhombohedral structure is attributed to the presence of OH − and H 2 O defects in the NKN platelets. The piezoelectric strain constant ( d 33 ) of NKN platelets synthesized at 600°C for 12 h is 100 pmV −1 , whereas that of NKN platelets synthesized at 500°C is lesser (50 pmV −1 ) due to the presence of these defects. Piezoelectric nanogenerators (PNGs) are fabricated using composites consisting of NKN platelets and polydimethylsiloxane. A large output voltage of 25 V and output current of 2.7 μA were obtained for the PNG with NKN platelets synthesized at 600°C for 6 h. This PNG shows a high output electrical energy of 3.0 μW at an external load of 5.1 MΩ.

Description: We report a novel strategy to improve the dielectric properties of the biferroic YCrO 3 ceramic compound through interface conduction control by means of an insulating Al 2 O 3 using a core-shell design. The YCrO 3 particles were covered with several layers of insulating Al 2 O 3 using the atomic layer deposition technique to produce the core-shell structure. TEM images reveal homogeneous and well-defined Al 2 O 3 coatings of ~8, ~60, and ~130 nm thickness. XRD shows the Al 2 O 3 -shell to be amorphous. The dielectric characteristics of the sintered nano-composite were investigated in the 100 Hz–1 MHz frequency range and temperature between 300 and 580 K. As the Al 2 O 3 -shell thickness covering the YCrO 3 particles is increased, a decrease of the dielectric permittivity, loss tangent and AC conductivity values was found in the whole range of temperatures and frequencies. Furthermore, the rounded hysteresis loop, typical of conductive ceramic is restored as the insulating Al 2 O 3 layer becomes thicker. This behavior is explained because the insulating Al 2 O 3 -shell acts as internal barrier layer localizing the surface charges on the sintered grain boundaries. This fact was confirmed by Electron Beam Induced Current technique where a clear contrast at the grain boundaries confirms the charge localization at the YCrO 3 /Al 2 O 3 interface. These results also reveal that the Al 2 O 3 -shell induces another conductive mechanism when the insulating Al 2 O 3 layer becomes thicker. Nonetheless, this new strategy is an effective approach to suppress the parasitic conductivity in polycrystalline multiferroic ceramics and increasing thus the multifuncionality.

Description: Archeological campaigns along the track of the Domitian road in Cuma resulted in the recovery of a large amount of potshards and crucible fragments (both open and closed forms), covered with residues of blue and green frits, respectively. Typological analysis of the crucibles combined with mineralogical and petrological analyses on the ceramic body and frit residues revealed that the forms are intimately related to the technological data. Newly formed calcium silicates indicate high firing treatments of crucibles during pigment making (not lower than 950°C). In particular, different working temperatures for the two types of crucibles have been estimated by the presence/absence of sodalite-nosean feldspathoid. This mineral formed after the reaction of Si-Al-rich material (the sintered ceramic body) and alkalis transferred to ceramics via chemical diffusion during the pigment synthesis. Thus, the estimated working temperatures are higher for closed forms (〉1100°C) and lower for the open ones (950–1050°C). This different thermal treatment perfectly fits with the temperatures of green and blue pigment synthesis; higher temperatures for green pigments allowed the formation of abundant Cu-bearing glassy phase, whereas, blue pigment is prone to the formation and thermal stability of cuprorivaite crystals (950–1050°C). Moreover, the two frits showed similar recipes (quartz-feldspar-calcite-rich sand) with the exception of more abundant Cu-bearing colorant agent in blue hue and higher proportion of alkaline flux in green frit. The obtained data suggested that crucibles were a fundamental tool for pigment manufacturing, likely one of the best example of ancient technical ceramics, as they permitted controlling the temperatures along with the fuel and the treatment time. Combining analytical and archeological data, the production and the technology of the two colored compounds identified as Egyptian Blue and Green frits in ancient Cuma has been inferred. Finally, considering the Vitruvius excerpt that identified an Egyptian Blue production in Puteoli , the area of production can be widen up to the northern Phlegraean Fields, also including Cumae and Liternum.

Description: Many functional properties of perovskite oxides, ABO 3 , have a close relationship with their subtle structures, especially, the distortions of BO 6 octahedra. As perovskite oxide heterostructures offer a good platform for controlling functional properties, it is important to understand the coupling between strain and oxygen octahedral distortions across the interface. Here, we study the coupling between the interfacial strain and oxygen octahedral distortions in GdScO 3 /SrTiO 3 heterostructure using aberration-corrected transmission electron microscopy (AC-TEM) with sub-Angstrom resolution and complementary first-principle calculation. Our results reveal that the shape rather than tilting angle of octahedra is strongly modified by the interfacial strain. These results would conduct us to deeply understand the strain-octahedral distortion coupling mechanism, and tune functionalities of perovskite oxide thin film in a more elaborate way which is related to the geometry of cation–oxygen bond.

Description: Y-doped BaZrO 3 (BZY) is a promising candidate as an electrolyte in fuel cells, and attracts increasing attention. In this work, a systematic investigation was performed on microstructure, proton concentration, proton conductivity, and hydration induced chemical expansion in Y-doped BaZrO 3 . The results revealed that the bimodal microstructure in BaZr 0.85 Y 0.15 O 3−δ was composed of large grains with composition close to the nominal value, and fine grains with large compositional discrepancy. This property is considered to be one of the evidences of phase separation at lower temperature than sintering temperature (1600°C), which hinders the grain growth. Thermal expansion coefficient of BZY was measured for various dopant level, and was determined to be around 10 −5 K −1 in wet and dry argon atmosphere. In addition, chemical expansion effect due to hydration was confirmed by HT-XRD in dry and wet Ar atmospheres, and suggests an interesting relationship between the lattice change ratio and proton concentration, in the BZY system with different Y content. The change ratio of lattice constant due to hydration increased obviously with the proton concentration for the sample containing the Y content of 0.02 and 0.05, but only changed slightly when the Y content was increased to 0.1 and 0.15. However, when the Y content was further increased over 0.2, the change ratio of lattice constant due to hydration starts to increase obviously again. Such results indicate a high possibility that the stable sites of protons in BZY changed with the variation in Y content.

Description: The thermal expansion of Dy 2 TiO 5 in the hexagonal phase was evaluated and compared with the orthorhombic phase using in situ high-temperature X-ray diffraction. The crystal structure, volume changes before and after the transformation process, as well as the mechanism behind the thermal expansion behavior was determined and proposed. It was found that in the hexagonal phase, the thermal expansion was caused by the oxygen anions in the axial positions of the trigonal bipyramidal structure moving toward the central Ti atom. While expanding, the movement of these oxygen anions slows the expansion along the c -axis resulting in a decrease in α 33 with temperature. Furthermore, a structural relationship between the orthorhombic and the hexagonal phases was proposed.

Description: A widely adopted approach to form matched seals in metals having high coefficient of thermal expansion (CTE), e.g. stainless steel, is the use of high CTE glass-ceramics. With the nucleation and growth of Cristobalite as the main high-expansion crystalline phase, the CTE of recrystallizable lithium silicate Li 2 O–SiO 2 –Al 2 O 3 –K 2 O–B 2 O 3 –P 2 O 5 –ZnO glass-ceramic can approach 18 ppm/°C, matching closely to the 18 ppm/°C–20 ppm/°C CTE of 304L stainless steel. However, a large volume change induced by the α-β inversion between the low- and high- Cristobalite, a 1 st order displacive phase transition, results in a nonlinear step-like change in the thermal strain of glass-ceramics. The sudden change in the thermal strain causes a substantial transient mismatch between the glass-ceramic and stainless steel. In this study, we developed new thermal profiles based on the SiO 2 phase diagram to crystallize both Quartz and Cristobalite as high expansion crystalline phases in the glass-ceramics. A key step in the thermal profile is the rapid cooling of glass-ceramic from the peak sealing temperature to suppress crystallization of Cristobalite. The rapid cooling of the glass-ceramic to an initial lower hold temperature is conducive to Quartz crystallization. After Quartz formation, a subsequent crystallization of Cristobalite is performed at a higher hold temperature. Quantitative X-ray diffraction analysis of a series of quenched glass-ceramic samples clearly revealed the sequence of crystallization in the new thermal profile. The coexistence of two significantly reduced volume changes, one at ~220°C from Cristobalite inversion and the other at ~470°C from Quartz inversion, greatly improves the linearity of the thermal strains of the glass-ceramics, and is expected to improve the thermal strain match between glass-ceramics and stainless steel over the sealing cycle.

Description: PdO-decorated SnO 2 nanocomposites with open porous hierarchical architectures are fabricated through a facile biotemplating sol–gel technique. The sol–gel soakage process is carried out by immersing the templates butterfly wings in Sn- and Pd- impregnants successively to generate a uniform colloid layer. PdO and SnO 2 nanocrystallites come into being with subsequent calcination treatment, and PdO-decorated SnO 2 nanocomposites further construct the parallel main ridges with connective pillars and vertical struts, finally present a 3-D open porous hierarchical architecture. Benefiting from unique ingredients and structure hierarchy, the nanocomposites give enhanced acetone-sensing performance of high sensitivity and rapid response/recovery rate

Description: Bi 0.98 Na 0.02 Fe 1− x Ru x O 3 ( x = 0, 0.01, 0.02) samples were prepared via a sol–gel method. The formation of the desired materials was confirmed using X-ray diffraction. The tetravalent Ru doping could effectively reduce the number of oxygen vacancy, and subsequently reduce the leakage current. Interestingly, the optical band gap was narrowed gradually in our samples, which seems contradictory with the variation in oxygen vacancy. To better understand this abnormal optical property, the effect of bandwidth was analyzed based on the change in Fe–O bond length and Fe–O–Fe bond angle, and the corresponding phenomenological qualitative model was proposed. The magnetization was increased with Ru substitution. In addition, an exchange bias (EB) phenomenon without field cooled process was observed at room temperature for all the samples, which was explained by introducing a core–shell structure model. Moreover, the EB behavior becomes more pronounced at 5 K for 1% Ru-doped sample.

Description: A micro four-layer SiC coating, which includes inner transition layer, fine-grained layer, dense bulk layer, and outer loose layer, was fabricated on the matrix graphite spheres of high-temperature gas-cooled reactor fuel elements to improve the oxidation-resistant property by a two-step pack cementation process. According to the experiment results, the micro four-layer can be differentiated by SiC grain size and microstructure variation. The oxidation tests at 1773 K for 200 h reveal that the coating structure could effectively improve the oxidation resistance of matrix graphite spheres with a weight gain of 0.52 wt%, and the fine-grained and dense bulk layers are evidenced as two main antioxidation layers. Although the thermal expansion coefficients of SiC and matrix graphite do not match each other so well, no obvious stress cracking was observed after thermal shocking tests from 1773 K to room temperature for 100 times.

Description: Despite the excellent thermochemical properties of magnesia carbon bricks, these exhibit one weak characteristic during their use: their carbothermally induced wear. Carbon has a high affinity to oxygen, which leads to a reaction between magnesia and carbon, forming gaseous products at very low oxygen partial pressures in the surrounding atmosphere. When magnesia carbon material is furthermore applied at negative pressures, the precited carbothermic reduction processes effect an internal decomposition or even degradation of the bricks. Mostly, high-purity magnesia varieties (MgO ≥ 96 wt%) are used for the production of magnesia carbon bricks because the low-melting calcium silicate secondary phases in magnesia impair the high-temperature resistance of these bricks. The fundamental question if and to which extent secondary phases react with carbon and which impact they have on the carbothermally induced wear of bricks has been unsolved so far. The following paper presents which influence the mineral secondary phases, monticellite, merwinite, and belite that are most commonly occurring in magnesia, have on the carbothermally induced wear. The respective studies were conducted by means of thermogravimetric and microstructural analyses. The results of these studies show that monticellite in the MgO–C microstructure brings about an increase in weight loss on account of carbothermic reduction processes. On the contrary, belite and merwinite in the MgO–C structure do not exhibit any negative impact on the thermal stability of the microstructure.

Description: Low-fired cobalt niobate (CoNb 2 O 6 ) microwave dielectric ceramics were prepared through a developed sol–gel process using Nb 2 O 5 · n H 2 O as starting source. A metal-dioxo-bridged complex precursor was described on the basis of FT-IR spectrum. The crystalline phases of calcined powders were characterized by X-ray diffraction. Nanosized CoNb 2 O 6 particles with orthorhombic α-PbO 2 -type structure were obtained above 750°C. There was no subsequent phase change upon sintering, and all compounds sintered to at least 94% of theoretical density. At 1000°C/4 h, CoNb 2 O 6 ceramics exhibited ε r ~ 21.9, Q × f ~ 66 140 GHz (at 8.9 GHz) and τ f ~ −39.7 ppm/°C, having a good potential for low-temperature cofired ceramic applications.

Description: Microstructural evolution during the devitrification of amorphous tantalum thin films synthesized via pulsed laser deposition was investigated using in situ transmission electron microscopy (TEM) combined with ex situ isothermal annealing, bright-field imaging, and electron-diffraction analysis. The phases formed during crystallization and their stability were characterized as a function of the chamber pressure during deposition, devitrification temperature, and annealing time. A range of metastable nanocrystalline tantalum oxides were identified following devitrification including multiple orthorhombic oxide phases, which often were present with, or evolved to, the tetragonal TaO 2 phase. While the appearance of these phases indicated the films were evolving to the stable form of tantalum oxide—monoclinic tantalum pentoxide—it was likely not achieved for the conditions considered due to an insufficient amount of oxygen present in the films following deposition. Nevertheless, the collective in situ and ex situ TEM analysis applied to thin film samples enabled the isolation of a number of metastable tantalum oxides. New insights were gained into the transformation sequence and stability of these nanocrystalline phases, which presents opportunities for the development of advanced tantalum oxide-based dielectric materials for novel memristor designs.

Description: The purpose of this work was to study the role of lithium in cesium-based geopolymers and the thermal evolution during heat treatment together with thermal expansion behavior of the resulting geopolymer ceramic. A series of lithium-substituted cesium-based geopolymers, Cs (1− x ) Li x GP (where x = 0, 0.1, 0.2, and 0.3), were prepared. All the geopolymer samples were heated at 1300°C for 2 h and thermal evolution on heating was studied by a variety of techniques. Phase composition, microstructure evolution, and thermal expansion behaviors of the ceramics derived from the geopolymers were characterized. All the geopolymer specimens exhibited similar thermal evolutionary trends. With increases in lithium content, overall mass loss increased gradually due to the higher hydration energy of Li + than Cs + . Thermal shrinkage of these specimens can be divided into four stages, i.e., structural resilience, dehydration, dehydroxylation, and sintering, according to the dilatometer results. The introduction of Li results in two-step sintering behavior for the lithium-substituted cesium-based geopolymers. The average thermal expansion coefficient (CTE) of Cs (1− x ) Li x GP ceramics decreased from 4.80 × 10 −6 K −1 ( x = 0) to 3.61 × 10 −6 K −1 ( x = 0.3) with increase in lithium substitution. The reason can be attributed to the presence of spodumene after thermal treatment, which has a relatively low thermal expansion coefficient compared with pollucite. Meanwhile, molten spodumene could serve as a buffer phase between pollucite crystals also conducive to the decline of CTE of this system.