Showing papers in "Journal of the American Ceramic Society in 2016"
TL;DR: In this article, the cold sintering process (CSP) was used to achieve dense ceramic solids at extraordinarily low temperatures of <300°C. But, although a number of new techniques have been developed, the process is still performed at high temperatures.
Abstract: Research on sintering of dense ceramic materials has been very active in the past decades and still keeps gaining in popularity. Although a number of new techniques have been developed, the sintering process is still performed at high temperatures. Very recently we established a novel protocol, the “Cold Sintering Process (CSP)”, to achieve dense ceramic solids at extraordinarily low temperatures of <300°C. A wide variety of chemistries and composites were successfully densified using this technique. In this article, a comprehensive CSP tutorial will be delivered by employing three classic ferroelectric materials (KH2PO4, NaNO2, and BaTiO3) as examples. Together with detailed experimental demonstrations, fundamental mechanisms, as well as the underlying physics from a thermodynamics perspective, are collaboratively outlined. Such an impactful technique opens up a new way for cost-effective and energy-saving ceramic processing. We hope that this article will provide a promising route to guide future studies on ultralow temperature ceramic sintering or ceramic materials related integration.
233 citations
TL;DR: In this paper, two two-dimensional Nb4C3-based solid solutions (MXenes), (Nb-0.8,Ti- 0.2)(4)C3Tx, and (nb-1.2,Ti 0.6,Zr 0.4,0.2), where T is a surface termination, were synthesized and confirmed by X-ray diff...
Abstract: Herein, two new two-dimensional Nb4C3-based solid solutions (MXenes), (Nb-0.8,Ti-0.2)(4)C3Tx and (Nb-0.8,Zr-0.2)(4)C3Tx (where T is a surface termination) were synthesizedas confirmed by X-ray diff ...
191 citations
TL;DR: In this article, CsPbBr3 quantum dots were precipitated in phosphate glasses through heat treatment, and the controlled formation of quantum dots was realized by adjustment of heat-treatment conditions.
Abstract: CsPbBr3 quantum dots were precipitated in phosphate glasses through heat treatment. Controlled formation of CsPbBr3 quantum dots was realized by adjustment of heat-treatment conditions. Absorption and photoluminescence spectra of CsPbBr3 quantum dots were tuned from 432 to 521 nm. Upon ultraviolet or blue light excitation, efficient photoluminescence from these CsPbBr3 quantum dots doped phosphate glasses was observed.
168 citations
TL;DR: In this article, the intrinsic limits of ferroelectric response, the roles of electrical and mechanical boundary conditions, grain size and thickness effects, and extraneous effects related to processing are reviewed.
Abstract: Ferroelectric materials are well-suited for a variety of applications because they can offer a combination of high performance and scaled integration. Examples of note include piezoelectrics to transform between electrical and mechanical energies, capacitors used to store charge, electro-optic devices, and nonvolatile memory storage. Accordingly, they are widely used as sensors, actuators, energy storage, and memory components, ultrasonic devices, and in consumer electronics products. Because these functional properties arise from a noncentrosymmetric crystal structure with spontaneous strain and a permanent electric dipole, the properties depend upon physical and electrical boundary conditions, and consequently, physical dimension. The change in properties with decreasing physical dimension is commonly referred to as a size effect. In thin films, size effects are widely observed, whereas in bulk ceramics, changes in properties from the values of large-grained specimens is most notable in samples with grain sizes below several micrometers. It is important to note that ferroelectricity typically persists to length scales of about 10 nm, but below this point is often absent. Despite the stability of ferroelectricity for dimensions greater than ~10 nm, the dielectric and piezoelectric coefficients of scaled ferroelectrics are suppressed relative to their bulk counterparts, in some cases by changes up to 80%. The loss of extrinsic contributions (domain and phase boundary motion) to the electromechanical response accounts for much of this suppression. In this article, the current understanding of the underlying mechanisms for this behavior in perovskite ferroelectrics is reviewed. We focus on the intrinsic limits of ferroelectric response, the roles of electrical and mechanical boundary conditions, grain size and thickness effects, and extraneous effects related to processing. In many cases, multiple mechanisms combine to produce the observed scaling effects.
139 citations
TL;DR: A brief chronicle of the first half century of translucent and transparent ceramics can be found in this article, where the main ceramic materials now available in a transparent state are presented and their main applications are described.
Abstract: Fifty years have elapsed from the moment the first light transmitting ceramic-based commercial item—a sodium vapor-based street lamp component—reached the market. This paper intends to be a brief chronicle (albeit not a chronology) of this first half century of translucent and transparent ceramic history. The main ceramic materials now available in a transparent state are presented and their main applications are described. Applications range from aerospace and relativistic optics to medical care, supermarket shopping, and modern warfare. Light transmitting ceramics usable as laser gain-media, armor windows, IR domes, phosphors, scintillators, and electro-optical components have been developed. The principal achievements this research produced are discussed. Processing strategies for full densification have been devised and quantitative relationships were established between different microstructural features such as amount and size distribution of porosity or level of birefringence, and the level of electromagnetic radiation attenuation they cause. Future prospects list ends the paper.
131 citations
TL;DR: In this article, the effect of relative density on the hardness and fracture toughness of Al-substituted cubic garnet Li6.19Al0.27La3Zr2O12 (LLZO) was investigated.
Abstract: The effect of relative density on the hardness and fracture toughness of Al-substituted cubic garnet Li6.19Al0.27La3Zr2O12 (LLZO) was investigated. Polycrystalline LLZO was made using solid-state synthesis and hot-pressing. The relative density was controlled by varying the densification time at fixed temperature (1050°C) and pressure (62 MPa). After hot-pressing, the average grain size varied from approximately 2.7–3.7 μm for the 85% and 98% relative density samples, respectively. Examination of fracture surfaces revealed a transition from inter- to intragranular fracture as the relative density increased. The Vickers hardness increased with relative density up to 96%, above which the hardness was constant. At 98% relative density, the Vickers hardness was equal to the hardness measured by nanoindentation 9.1 GPa, which is estimated as the single-crystal hardness value. An inverse correlation between relative density and fracture toughness was observed. The fracture toughness increased linearly from 0.97 to 2.37 MPa√m for the 98% and 85% relative density samples, respectively. It is suggested that crack deflection along grain boundaries can explain the increase in fracture toughness with decreasing relative density. It was also observed that the total ionic conductivity increased from 0.0094 to 0.34 mS/cm for the 85%–98% relative density samples, respectively. The results of this study suggest that the microstructure of LLZO must be optimized to maximize mechanical integrity and ionic conductivity.
124 citations
TL;DR: In this article, it was shown that the transition to a highly nonlinear rise in electrical conductivity, a signature event for the onset of the flash, occurs within a narrow range of power density.
Abstract: The large bank of data for ceramics from experiments in flash sintering reveal a surprising characteristic: that the transition to a highly nonlinear rise in electrical conductivity—a signature event for the onset of the flash—occurs within a narrow range of power density. This condition holds for ceramics that are semiconductors, ionic conductors, electronic conductors, and insulators.They flash at temperatures that range from 300°C to 1300°C, and at electric fields from 10 V/cm to over 1000 V/cm. Yet, the power expenditure at the transition for all of them still falls within this narrow range. This, rather uniform value of power dissipation suggests that Joule heating is a key factor in instigating the flash. A general formulation is developed to test if indeed Joule heating alone can lead to the progression of such nonlinear behavior. It is concluded that Joule heating is a necessary but not a sufficient condition for flash sintering.
118 citations
TL;DR: In this article, rare-earth (RE) monosilicates are used as environmental barrier coating (EBC) materials for ceramic matrix composites for aerospace applications, and relative densities above 94% were obtained for all samples and ceramics were made containing 85-100 wt% of the rare earth (RE)-monosilicate according to X-ray diffraction (XRD).
Abstract: Rare-earth (RE) monosilicates are promising candidates as environmental barrier coating (EBC) materials for ceramic matrix composites for aerospace applications. Five rare-earth monosilicate materials have been investigated: Y2SiO5, Gd2SiO5, Er2SiO5, Yb2SiO5, and Lu2SiO5 produced from RE oxides and silica starting materials pressed and sintered at 1580°C under flowing air. Relative densities above 94% were obtained for all samples and ceramics were made containing 85–100 wt% of the RE monosilicate according to X-ray diffraction (XRD) with RE disilicates as the second phase in the Gd, Yb, and Lu silicate systems. Microstructures were characterized using scanning electron microscopy and XRD, and thermal properties measured including specific heat, thermal expansion, and thermal diffusivity. For the first time, specific heat capacity values are reported for the monosilicates [0.45–0.69 J·(g·K)−1]. Thermal expansion coefficients (TECs) of the dense samples ranged between 5.9 and 10.3 × 10−6 K−1 measured for 473 to 1473 K. All EBCs have low thermal conductivities [1.8 W·(m·K)−1 or less] making them excellent EBC insulators.
110 citations
TL;DR: In this paper, Li2SrSiO4 (LSS) phosphors with blue, red, and near-infrared (NIR) tri-emission have been prepared via a high-temperature solid-state reaction method.
Abstract: Ce3+/Pr3+ codoped Li2SrSiO4 (LSS) phosphors with blue, red, and near-infrared (NIR) tri-emission have been prepared via a high-temperature solid-state reaction method. Under the excitation of 200 to 400 nm near-ultraviolet (n-UV), the photoluminescence (PL) spectra of phosphors are composed of visible and NIR two parts. The former exhibits blue and red emission bands centered at around 428 nm from 5d–4f transition of Ce3+ and 611 nm from 1D2 → 3H4 transition of Pr3+, those overlap with photosynthesis action spectra of plants and absorption spectra of chlorophylls and carotenoids. While the later presents a broad NIR emission band peaking near 1039 nm caused by the 1G4 → 3H4 of Pr3+, matching with the absorption of bacteriochlorophyll. Their emission intensity ratios (B: R: NIR) could be tuned by altering the relative ratios of Ce3+ and Pr3+ concentration in the phosphors to meet the requirements of multifarious plants and bacteria. The efficient energy transfer from Ce3+ to Pr3+ takes place in the LSS host, which ascribed to an exchange interaction according to PL spectra and decay curves of phosphors. Results suggest that the present LSS: Ce3+, Pr3+ phosphors have great potential applications in plant growth n-UV LED.
104 citations
TL;DR: In this paper, microstructural statistics for 3 mol% yttria-stabilized zirconia synthesized by both conventional sintering and flash-sintering with AC and DC current were obtained.
Abstract: 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.
92 citations
TL;DR: In this paper, the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO3-Bi(M)O3 dielectrics as well as the processing challenges and opportunities associated with these materials are reviewed.
Abstract: As part of a continued push for high permittivity dielectrics suitable for use at elevated operating temperatures and/or large electric fields, modifications of BaTiO3 with Bi(M)O3, where M represents a net-trivalent B-site occupied by one or more species, have received a great deal of recent attention. Materials in this composition family exhibit weakly coupled relaxor behavior that is not only remarkably stable at high temperatures and under large electric fields, but is also quite similar across various identities of M. Moderate levels of Bi content (as much as 50 mol%) appear to be crucial to the stability of the dielectric response. In addition, the presence of significant Bi reduces the processing temperatures required for densification and increases the required oxygen content in processing atmospheres relative to traditional X7R-type BaTiO3-based dielectrics. Although detailed understanding of the structure–processing–property relationships in this class of materials is still in its infancy, this article reviews the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO3-Bi(M)O3 dielectrics as well as the processing challenges and opportunities associated with these materials.
TL;DR: In this paper, a flash event was attributed to the sharp positive temperature dependence of the electrical conductivity (thermal runaway) of SiC, and a sudden increase in electric power absorption (Joule heating) of the samples after a sufficient preheating temperature (>600°C) was reached.
Abstract: A novel processing methodology that allows combined preheating and Flash-SPS (FSPS) of silicon carbide-based materials has been developed. Beta-SiC (+10 wt% B4C) powders were densified (Ф 20 mm) up to 96% of their theoretical density in 17 s under an applied pressure of 16 MPa (5 kN). The flash event was attributed to the sharp positive temperature dependence of the electrical conductivity (thermal runaway) of SiC, and a sudden increase in electric power absorption (Joule heating) of the samples after a sufficient preheating temperature (>600°C) was reached. The microstructural evolution was analyzed by examining materials densified by FSPS in the range of 82%–96% theoretical densities. FEM modeling results suggest that the FSPS heating rate was of the order of 8800°C/min. A comparative analysis was done between FSPS and reference samples (sintered using conventional SPS in the temperature range of 1800°C–2300°C). This allowed for a better understanding of the temperatures generated during FSPS, and in turn the sintering mechanisms. We also demonstrated the scalability of the FSPS process by consolidating a large α-SiC disk (Ф 60 mm) in about 60 s inside a hybrid SPS furnace equipped with an induction heater, which allowed us to achieve sufficient preheating (1600°C) of the material to achieve FSPS.
TL;DR: In this paper, a systematic investigation was performed on microstructure, proton concentration, propton conductivity, and hydration induced chemical expansion in Y-doped BaZrO3.
Abstract: Y-doped BaZrO3 (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 BaZrO3. The results revealed that the bimodal microstructure in BaZr0.85Y0.15O3−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.
TL;DR: In this paper, single-phase monoclinic aluminum-gallium oxide powders, β−(AlxGa1−x)2O3, have been produced by solution combustion synthesis for Al fraction 0 ≤ ≥ 0.8.
Abstract: Single-phase monoclinic aluminum–gallium oxide powders, β−(AlxGa1−x)2O3, have been produced by solution combustion synthesis for Al fraction 0 ≤ x < 0.8. α−(AlxGa1−x)2O3 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.
TL;DR: In this article, the effects of Bi3+ nonstoichiometry on microstructure, dielectric, ferroelectric, and piezoelectric properties were studied.
Abstract: 0.94(Na0.5Bi0.5+x)TiO3–0.06BaTiO3 (x = −0.04, 0, 0.02; named NB0.46T-6BT, NB0.50T-6BT, NB0.52T-6BT, respectively) lead-free piezoelectric ceramics were prepared via the solid-state reaction method. Effects of Bi3+ nonstoichiometry on microstructure, dielectric, ferroelectric, and piezoelectric properties were studied. All ceramics show typical X-ray diffraction peaks of ABO3 perovskite structure. The lattice parameters increase with the increase in the Bi3+ content. The electron probe microanalysis demonstrates that the excess Bi2O3 in the starting composition can compensate the Bi2O3 loss induced during sample processing. The size and shape of grains are closely related to the Bi3+ content. For the unpoled NB0.50T-6BT and NB0.52T-6BT, there are two dielectric anomalies in the dielectric constant–temperature curves. The unpoled NB0.46T-6BT shows one dielectric anomaly accompanied by high dielectric constant and dielectric loss at low frequencies. After poling, a new dielectric anomaly appears around depolarization temperature (Td) for all ceramics and the Td values increase with the Bi3+ amount decreasing from excess to deficiency. The diffuse phase transition character was studied via the Curie–Weiss law and modified Curie–Weiss law. The activation energy values obtained via the impedance analysis are 0.69, 1.05, and 1.16 eV for NB0.46T-6BT, NB0.50T-6BT and NB0.52T-6BT, respectively, implying the change in oxygen vacancy concentration in the ceramics. The piezoelectric constant, polarization, and coercive field of the ceramics change with the variation in the Bi3+ content. The Rayleigh analysis suggests that the change in electrical properties of the ceramics with the variation in the Bi3+ amount is related to the effect of oxygen vacancies.
TL;DR: In this paper, 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.
Abstract: 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.
TL;DR: In this article, the temperature-dependent energy storage and dielectric properties of Pb0.O3 were investigated and it was shown that the vanishment of high-electric-field nonlinear polarization contributions causes the declination of releasable energy with the temperature rise.
Abstract: The temperature-dependent energy storage and dielectric properties of Pb0.90La0.04Ba0.04[(Zr0.7Sn0.3)0.88Ti0.12]O3 were investigated in this work. With the phase transition from antiferroelectric to paraelectric induced by temperature rise, the releasable energy density decreases from 0.74 J/cm3 (20°C) to 0.29 J/cm3 (140°C), whereas the discharge efficiency increases from 75.0% to 93.4%. The pulsed discharge current indicates that the stored energy can be released in less than 1 μs. The temperature has little impact on the amplitude of the current but influences the discharge duration time greatly. In addition, with the comprehensive analysis of hysteresis loops, the DC-bias character of dielectric constant and the discharge current, the transition from strong nonlinearity to linearity of the dielectric along with the phase switching was confirmed. It proves that the vanishment of high-electric-field nonlinear polarization contributions causes the declination of releasable energy with the temperature rise.
TL;DR: Yb2SiO5 is a promising material for thermal/environmental barrier coatings (T/EBCs), and its mechanical and thermal properties, which are essential to the coating design and applications, are investigated in this paper.
Abstract: Yb2SiO5 is a promising material for thermal/environmental barrier coatings (T/EBCs), and its mechanical and thermal properties, which are essential to the coating design and applications, are investigated in this work. Yb2SiO5 has relatively high fracture toughness, bending and compressive strength, but low Young's modulus. It is also tolerant to damage, which is underpinned by grain delamination and cleavage along {100}, {001}, and {040} planes. The average linear coefficient of thermal expansion (CTE) is 6.3 × 10−6 K−1 (473–1673 K) and the anisotropic CTEs are: αa = (2.98 ± 0.16) × 10−6 K−1,αb = (6.51 ± 0.19) × 10−6 K−1, and αc = (9.08 ± 0.16) × 10−6 K−1. The thermal conductivities are 2.3 and 1.5 W (m·K)−1 at 300 and 1200 K, respectively. The unique combination of these properties warrants Yb2SiO5 promising for T/EBCs applications.
TL;DR: In this article, chemical and electronic properties of dielectric oxide interfaces as obtained using photoelectron spectroscopy are presented and discussed, which reveal the dependence of valence band maximum and conduction band minimum energies.
Abstract: Chemical and electronic properties of dielectric oxide interfaces as obtained using photoelectron spectroscopy are presented and discussed. Interface preparation includes the deposition of metals onto dielectrics and vice versa as well as the effect of postdeposition treatments. Most interfaces are not abrupt as either reduction in the oxide surface occurs during metal deposition or oxidation of the metal substrate is induced by oxide deposition. The Schottky barrier heights at these interfaces are strongly affected by the interface chemistry. Reactive interfaces exhibit a strong Fermi level pinning due to defect formation. Nonreactive interfaces, which are obtained by depositing metallic oxide electrodes, exhibit an unpinned Schottky–Mott-like barrier formation. Barrier heights can therefore be modified by more than 1 eV with suitable electrode material and processing. Postdeposition oxidation and reduction treatments and ferroelectric polarization can lead to comparable changes of barrier height. Interface studies between dielectric oxides reveal the dependence of valence band maximum and conduction band minimum energies. Due to transitivity of band alignment, these can be arranged on an absolute energy scale. The range of Fermi level positions in dielectric oxides, which can also be obtained from photoelectron spectroscopy and which is limited by intrinsic defect formation, is comparable when the oxides aligned on the energy scale determined by the photoemission experiments. The band alignment therefore indicates if a material can be made n-type or p-type by donor or acceptor doping. The range of Fermi levels in the oxides corresponds also with the range of the Fermi levels at oxide/metal interfaces.
TL;DR: In this paper, the temperature dependence of dielectric permittivity of pure perovskite K0.5NbO3-xSrTiO3 (x = 0.016) was analyzed using the Lorentz-type relation fitting, which revealed that the polar nanoregions contributed to the nonlinear e(E) dependencies.
Abstract: Pure perovskite K0.5Na0.5NbO3–xSrTiO3 (x = 0.16, 0.17, 0.18, and 0.19) ceramics were prepared by using a solid-state reaction process. The ceramics were optically transparent for visible and near-infrared wavelengths. Then, high tunability (24.1%) and low dielectric loss (0.016) for the x = 0.18 sample indicated the transparent ceramics could be used in tunable devices. The Lorentz-type relation fitting for the temperature dependence of dielectric permittivity showed that these ceramics had a typical relaxor behavior, and the polar nanoregions were related to the tunable dielectric properties. The nonlinear dielectric behavior was further explored by the Johnson model combined with Langevin terms, which revealed that the polar nanoregions contributed to the nonlinear e(E) dependencies with contributions of 12.3%, 11.6%, 5.9%, and 3.6% for x = 0.16, 0.17, 0.18, and 0.19, respectively.
TL;DR: In this article, the sintering of a ceramic can take place at temperatures below 200°C, using aqueous solutions as transient solvents to control dissolution and precipitation and enable densification.
Abstract: Conventional thermal sintering of ceramics is generally accomplished at high temperatures in kilns or furnaces. We have recently developed a procedure where the sintering of a ceramic can take place at temperatures below 200°C, using aqueous solutions as transient solvents to control dissolution and precipitation and enable densification (i.e., sintering). We have named this approach as the “Cold Sintering Process” because of the drastic reduction in sintering temperature and time relative to the conventional thermal process. In this study, we fabricate basic monolithic capacitor array structures using a ceramic paste that is printed on nickel foils and polymer sheets, with silver electrodes. The sintered capacitors, using a dielectric Lithium Molybdenum Oxide ceramic, were then cold sintered and tested for capacitance, loss, and microstructural development. Simple structures demonstrate that this approach could provide a cost-effective strategy to print and densify different materials such as ceramics, polymers, and metals on the same substrate to obtain functional circuitry.
TL;DR: In this article, an aqueous-based sol-gel method with spontaneous sol and gel formation is developed, which can be applied on a large scale to synthesize compounds with Ti4+ and PO43−.
Abstract: Sol–gel synthesis is an extensively used method for the preparation of nanopowders. However, complicated or expensive precursors, and the necessity of using organic solvent and/or heat assistance limit the method to laboratory-scaled level. An aqueous-based sol–gel method with spontaneous sol and gel formation is developed in this study. It can be applied on a large scale to synthesize compounds with Ti4+ and PO43− as major components with low cost. Al-substituted LiTi2(PO4)3 (LATP) has been widely investigated as a promising candidate for solid electrolyte in Li-ion or Li-air batteries. Major challenges such as unsatisfactory phase purity, low sintering activity, and high production costs are faced during the fabrication of LATP. In this study, as a sample application, Li1.5Al0.5Ti1.5(PO4)3 (LATP05) is conveniently prepared on a large scale by the novel sol–gel method with high phase purity, active densification behavior and high conductivity.
TL;DR: In this paper, the role of interfacial energies in the microstructure evolution of nanoparticles is discussed, in particular addressing them as parameters to allow better control in addition to more conventional kinetic parameters.
Abstract: Sintering and nanostability (defined as the stability against sintering) are critical phenomena present in the processing and application of nanoparticles. With important implications in obtaining high-quality dense ceramics with fine grains or in enabling high surface areas in nanoparticles for catalytic applications, the control of these interrelated phenomena has been the focuses of several studies. From a thermodynamic perspective, it is recognized that surface energy is a fundamental parameter in both cases, since it is the main driving force for sintering and also the reason that nanoparticles are thermodynamically unstable and have the tendency to coarsen at elevated temperatures. The role of grain-boundary energies is less recognized as relevant, but is also connected to densification, grain growth, and nanoparticle stability. In this paper, we review the critical aspects of the role of interfacial energies in the microstructure evolution, in particular addressing them as parameters to allow better control in addition to more conventional kinetic parameters. The concept is based on the nonsingularity of interfacial energies in a given system, which varies with temperature, atmosphere, and most importantly, chemical composition—this last offering a method to induce particular microstructural evolutions. While the model assumes isotropic grain boundaries but consequences to anisotropy are also discussed. The paper presents examples of the role of dopants on interfacial energies, how this is quantitatively related to their segregation at the interfaces, and the impact in sintering and nanostability. Given the importance of interface energetics to these phenomena, we also present a short review on the current methods used to obtain reliable interface thermodynamic data.
TL;DR: In this paper, a low AFE to FE switching field was obtained and its value could be adjusted by La chemical modification, which showed variable amount of antiferroelectric orthorhombic and ferroelectric (FE) rhombohedral phases.
Abstract: Polarization switching behavior and energy storage performances of (Pb1−xLax)(Zr0.90Ti0.10)1−x/4O3 (PLZT x/90/10) ceramics with La compositions across the ferroelectric/antiferroelectric phase boundary, which show variable amount of antiferroelectric (AFE) orthorhombic and ferroelectric (FE) rhombohedral phases, were investigated. A low AFE to FE switching field was obtained and its value could be adjusted by La chemical modification. While the PLZT system evolves from a FE state to an AFE state as a function of La content and from an AFE state to a FE state as a function of the applied electric field, the recoverable energy (Wre) and loss energy (Wloss) range between two limits whose lower and higher values are obtained for PLZT composition in AFE state and FE state, respectively. In terms of the extent of La-modification, the Wre has been enhanced from 0.819 J/cm3 (for PLZT 2/90/10 and electric field of ~30 kV/cm) to the highest value of 1.85 J/cm3 (for PLZT 3.5/90/10 and electric field ~65 kV/cm), followed by their subsequent reduction.
TL;DR: In this paper, the effects of macropore morphology and orientation on the mechanical properties of anisotropic porous ceramics were investigated using both freeze casting and slip casting, and the experimental results were rationalized using detailed microstructural analysis.
Abstract: Porous ceramics are commonly used in electrochemical, catalytic, biological, and filtration processes, but in many cases, improvements to their designed performance comes at the expense of their mechanical properties. By controlling the pore morphology and orientation, it is possible to mitigate some mechanical losses while maintaining adequately porous microstructures. Hierarchically, porous ceramics with similar porosities but differing macropore arrangements were synthesized using both freeze casting and slip casting, and then tested in compression to study the effects of macropore morphology and orientation on mechanical behavior. The mechanical properties of the anisotropic structures were a strong function of the orientation of the macropores relative to the applied stress. The properties of the isotropic hierarchical porous structures were in between the two orthotropic directions of the anisotropic porous ceramics. For the freeze-cast samples, the compressive strength was a function of the macropore size. The experimental results are rationalized using detailed microstructural analysis.
TL;DR: In this paper, the authors reported a simple, inexpensive method for synthesis of calcium hydroxide Ca(OH)(2)] nanoparticles (CHNPs) using chemical precipitation (CP) in aqueous medium at room temperature.
Abstract: The present work reports a simple, inexpensive method for synthesis of calcium hydroxide Ca(OH)(2)] nanoparticles (CHNPs). The method involves chemical precipitation (CP) in aqueous medium at room temperature. Calcium nitrate dihydrate Ca(NO3)(2).2H(2)O] and sodium hydroxide were used as precursors. The CHNPs were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Rietveld analysis, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), BET surface area evaluation as well as particle size distribution analysis techniques. The results confirmed the synthesis of CHNPs as the major phase. The CHNPs exhibited an average size of about 350 nm. In addition, some calcite phase formed due to the inevitable carbonation process. A very minor amount of aragonite phase was also present. A schematically developed new qualitative model is proposed to explain the genesis and subsequent evolution of the various phases at the nanoscale. The model helps to identify the rate-controlling step. It also highlights the implication of reaction kinetics control in synthesis of predesigned nanophase assembly.
TL;DR: In this paper, solid solutions of (1−x)BaTiO3−xBi(Mg2/3Nb1/3)O3 (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.
Abstract: Solid solutions of (1−x)BaTiO3–xBi(Mg2/3Nb1/3)O3 (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 (er). Optimum properties were obtained for x = 0.5 which exhibited a broad and stable relative er ~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(Mg2/3Nb1/3)O3 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.
TL;DR: In this paper, the feasibility to synthesize, in large quantity, pure and non-toxic tetrahedrite compounds using high-energy mechanical-alloying from only elemental precursors is reported.
Abstract: The feasibility to synthesize, in large quantity, pure and non-toxic tetrahedrite compounds using high-energy mechanical-alloying from only elemental precursors is reported in the present paper for the first time. Our processing technique allows a better control of the final product composition and leads to high thermoelectric performances (ZT of 0.75 at 700 K), comparable to that reported on sealed tube synthesis samples. Combined with spark plasma sintering, the production of highly pure and dense samples is achieved in a very short time, at least 8 times shorter than in conventional liquid-solid-vapor synthesis process. The process described in this paper is a promising way to produce high performance tetrahedrite materials for cost-effective and large-scale thermoelectric applications.