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Even though BiFeO3–BaTiO3 (BF–BT) with high Curie temperature and excellent piezoelectric properties is very suitable for high‐temperature applications, its rapid reduction in resistivity with temperature limits its further application. So far, there is no effective method to improve the resistivity of BF–BT at a high‐temperature state. In this work, hot‐press sintering combined with an oxygen atmosphere was used to prepare (1 − x)BF–xBT (x = 0.2–0.33) ceramics for the first time, which reduced the sintering temperature from 1000 to 920°C. The controllable grain size can be achieved by adjusting the sintering temperature and the applied pressure. The X‐ray photoelectron spectroscopy results confirmed that using hot‐press sintering effectively avoided the generation of heterovalent Fe ions, and the resistivity of BF–BT ceramics at the high‐temperature stage was improved by two orders of magnitude. It was found that hot‐press sintering can cause the oriented growth of the sample along the (1 1 0) direction, and further refined X‐ray diffraction was used to accurately analyze the changes in the lattice structure. The hot‐press sintered samples obtained larger polarization strength, especially the electro‐induced strain showed excellent temperature stability in the wide temperature range of 30–170°C. Hot‐pressing sintering combined with an oxygen atmosphere is more suitable for preparing high insulation and electrical breakdown resistance ceramics. [ABSTRACT FROM AUTHOR]

Infrared transparent Ce‐doped Y3Fe5O12 (Ce: YIG, CexY3‐xFe5O12, x = 0, 0.12, 0.24, 0.36) ceramics were successfully produced by the solid‐state reaction using a hot‐press sintering process from the Y2O3, Fe2O3, and CeO2 powders. The phase structure, microstructure, infrared transmittance, and magnetic and magneto‐optical properties of the Ce‐doped Y3Fe5O12 ceramics were measured and analyzed. The in‐line transmittances of the Ce‐doped Y3Fe5O12 ceramics with the x = 0, 0.12, 0.24 (L = 0.5 mm) at 1550 nm were about 72%, 66.5%, and 57.6%, respectively. In the state of saturation magnetization, the Faraday rotation angle per centimeter (θF) of CexY3‐xFe5O12 (x = 0, 0.12, 0.24) ceramics measured by the light extinction method was 182.5, −410.4, and −958.3 deg./cm, respectively. The change of the θF was about −142.5 deg./cm when per 1at.% Ce was substituted in the dodecahedral site of YIG materials. The (Ce0.24Y2.76)Fe5O12 ceramics were determined as the optimized composition for its excellent infrared optical and magneto‐optical properties. [ABSTRACT FROM AUTHOR]

(Pb0.87Ba0.1La0.02)(Zr0.68Sn0.24Ti0.08)O3 ( PBLZST) antiferroelectric ( AFE) ceramics have been prepared by hot-press sintering method and conventional solid-state reaction process, and the dependence of microstructure and energy storage properties of the ceramics on sintering approaches has been studied. The results reveal that not only the microstructure, but also the electrical properties of the PBLZST AFE ceramics are significantly improved by using the hot-press sintering method. Samples resulting from the hot-press sintering process have high breakdown strength of 180 kV/cm which results from the increase of density. Coupled with large polarization, the hot-pressed AFE ceramics are shown to have a high recoverable energy density of 3.2 J/cm3. The recoverable energy density of the hot-pressed PBLZST AFE ceramics is 100% greater than the conventional sintered specimens with recoverable energy density of 1.6 J/cm3. [ABSTRACT FROM AUTHOR]

The temperature stability of the electrocaloric effect ( ECE) in relaxor ferroelectric Pb0.85La0.1(Zr0.65Ti0.35)O3 ( PLZT) prepared by the hot-press sintering method has been investigated. Compared to the PLZTs prepared via the conventional sintering process, the hot-pressed PLZTs exhibit larger ECE and superior temperature stability. The hot-pressed sample with an appropriate content of excess PbO presents a high Δ T of 2.4°C and Δ S of 2.3 J kg−1·K−1, both of which are 30% greater than those of the conventionally sintered samples measured at 100 kV·cm−1. More importantly, the hot-pressed specimens display great stable electrical properties, including the dielectric breakdown strength and electrical resistivity in the temperature range from 0°C to 100°C, whose ECE instability, especially, is only one-half that of the samples prepared by the conventional solid-state method. In addition, the ECE and its stability of the hot-pressed sample can be further enhanced by increasing the operating electric field to a relatively high level of 200 kV·cm−1. This work demonstrates hot-press sintering is an effective method to fabricate ferroelectric ceramics with high ECE as well as desirable temperature stability. [ABSTRACT FROM AUTHOR]

La0.4Ni0.2Co3.8Sb12 filled skutterudite compound was successfully prepared via the route of mechanical alloying and hot pressing (MA-HP). Single-phase filled skutterudite can be obtained when the mechanically alloyed powders is hot pressed for 2 h at a temperature higher than 550°C. Prolonging the hot pressing process, the electrical resistivity of the La0.2Ni0.2 Co3.8Sb12 filled skutterudite decreases; Seebeck coefficient increases when the hot press duration is prolonged from 2 to 4 h, and no evident change was observed on further prolonging. A composite microstructure, which consists of some coral-like clusters and a nanocrystalline matrix with grain size about 50 nm in the La0.4Ni0.2Co3.8Sb12 filled skutterudite, was observed for the first time. The coral-like microstructure is thought to be the prime filled skutterudite phase produced directly by MA, while nanocrystalline matrix is the filled skutterudite phase formed during hot press. [ABSTRACT FROM AUTHOR]

The brittleness of Si3N4 ceramics has always limited its wide application. In this paper, Si3N4 ceramics were prepared based on foam. Combining the unique honeycomb structure of the ceramic foams and the self‐toughening mechanism of Si3N4, the strengthening and toughening of Si3N4 ceramics can be further achieved by adjusting the microstructure of Si3N4 ceramic foams. The powder particles are self‐assembled by particle‐stabilized foaming to form a foam body with a honeycomb structure. It was pretreated at different temperatures (1450–1750°C). The microstructure evolution of foamed ceramics at different pretreatment temperatures and the conversion rate of α‐Si3N4 to β‐Si3N4 at different pretreatment temperatures were explored. Then the foamed ceramics with different microstructures are hot‐press sintered to prepare Si3N4 dense ceramics. The effects of different microstructures of foamed ceramics on the strength and toughness of Si3N4 ceramics were analyzed. The experimental results show that the relative density of Si3N4 ceramics prepared at a particle pretreatment temperature of 1500°C is 97.8%, and its flexural strength and fracture toughness are relatively the highest, which are 1089 ± 60 MPa and 12.9 ± 1.3 MPa m1/2, respectively. Compared with the traditional powder hot‐pressing sintering, the improvement is 21% and 33%, respectively. It is shown that this method of preparing Si3N4 ceramics based on foam has the potential to strengthen and toughen Si3N4 ceramics. [ABSTRACT FROM AUTHOR]

The energy‐harvesting ability of the lead‐free ferroelectric Ba(Zr,Ti)O3 was investigated and greatly enhanced using the Kim novel electrothermodynamic cycle for low‐temperature application. Ba(Zr,Ti)O3 was synthesized with a Zr:Ti ratio of 10:90 (BZT10) by hot‐press sintering, which exhibited a mix relaxor‐ferroelectric behavior. For power generation using the Kim cycle with low and high temperatures of TL = 25°C, TH = 120°C, the most optimized temperature pattern occurred for a heating time of 12.5 s and a cooling time of 22.5 s. Under these conditions, the electric field increased during the novel isodisplacement process, and the displacement variation in the isoelectric step reached the highest value and maximized the BZT10 cycle loop area. Applying these conditions while lowering TL to 20°C, an energy density ND = 504 mJ/cm3 was achieved. This value is the highest obtained energy density in a practical test for lead‐free ferroelectric bulk material in the BaTiO3 family. [ABSTRACT FROM AUTHOR]

A type of boron nitride–magnesium aluminum silicate (BN‐MAS) composite ceramics was fabricated by hot‐press sintering at different sintering temperatures. The relationship between the sintering temperature and microstructure was investigated by analyzing the interaction between hexagonal boron nitride (h‐BN) and the MAS phase. The main MAS phase in the composite ceramics is the α‐cordierite phase at a sintering temperature of 1300°C. At temperatures above 1400°C, the inhibitory effect of h‐BN on the crystallization of the MAS system is significant, and MAS mainly exists in the form of an amorphous phase. The composite sintered at 1700°C exhibited the highest bending strength of 218MPa. h‐BN and MAS were co‐enhanced. MAS can be used as an effective liquid‐phase sintering aid to assist in the sintering of h‐BN, whereas h‐BN can absorb the fracture energy of the composite ceramics through the pull‐out and bridging effect of the particles. [ABSTRACT FROM AUTHOR]

Boron carbide (B4C) ceramic composites with excellent mechanical properties were fabricated by hot‐pressing using B4C, silicon carbide (SiC), titanium boride (TiB2), and magnesium aluminum silicate (MAS) as raw materials. The influences of SiC and TiB2 content on the microstructural evolution and mechanical properties of the composites were systematically investigated. The mechanism by which MAS promotes the sintering process of composites was also investigated. MAS exists in composites in the form of amorphous phase. It can effectively remove the oxide layer from the surface of ceramic particles during the high temperature sintering process. The typical values of relative density, hardness, bending strength, and fracture toughness of B4C–SiC–TiB2 composites are 99.6%, 32.61 GPa, 434 MPa, and 6.20 MPa m1/2, respectively. Based on the microstructure observations and finite element modeling, the operative toughening mechanism is mainly attributed to the crack deflection along the grain boundary, which results from the residual stress field generated by the thermal expansion mismatch between B4C and TiB2 phase. [ABSTRACT FROM AUTHOR]

In order to study the orientation dependence of the electrical properties of layered structure cathode materials used in lithium-ion thin-film microbatteries, a typical composition, LiCoO2, has been hot-press sintered in bulk with a strong crystallographic texture. Microstructural characterization using X-ray diffraction, scanning electron microscopy, and Raman spectroscopy showed that the degree of LiCoO2 texture depended upon the precise hot-press conditions used. There was a pronounced orientation of the polycrystalline LiCoO2 c-axis in the pressing direction with a high Lotgering factor ( f=0.96) for sintering at 950°C. The pronounced texture led to a remarkable anisotropy in electronic conductivity between directions parallel (σ∥) and perpendicular (σ⊥) to the pressing direction in the temperature range 190–400 K, with σ⊥/σ∥=187 at 300 K. The results suggest that texture can be used to tune not only the well-known electrochemical performance of all-solid-state lithium-ion thin-film batteries, but also their electronic conductivity. [ABSTRACT FROM AUTHOR]

This study addressed novel multiphase composite of Al2O3/Ti/TiC that exhibited enhanced fracture toughness and room‐temperature crack‐healing function. Al2O3/Ti/TiC composites were fabricated through hot‐press sintering of CNT, TiH2, and Al2O3 mixed powders, where the TiC was in‐situ formed by reaction of CNT and Ti. The effects of CNT (TiC) content on mechanical and electrical properties were studied. Electrochemical anodization process at room temperature was attempted to these composites to heal cracks introduced in the surface of composites. Results indicated that added CNT was invisible while metal Ti and reaction product TiC coexisted in all samples. The reaction between CNT and Ti[O] representing dissolved active oxygen into Ti was considered as the main formation route of TiC. The toughening mechanism was demonstrated as crack deflection and bridging due to the presence of TiC. In spite of the increase in electrical resistivity because of the higher resistivity of TiC than Ti, the present Al2O3/Ti/TiC composites still remain high enough electrical conductivity (8.0 × 10−3 Ωcm ~1.8 × 10−2 Ωcm for 0‐2 vol% CNT addition) which could be regarded as conductors; it allowed to heal cracks in the composites by electrochemical anodization that formed titanium dioxide phase at room temperature. It was found that crack‐healing ability in 1 vol% CNT added composite exhibited higher strength recovery ratio of 95.6% to the crack‐free sample than that of Al2O3/Ti composite (the recovery ratio of 89.6%). After crack‐healing process, mechanical strength of samples increased by 52.3% compared to cracked composites. It was concluded that the formed TiC could contribute to the appropriate electrical conduction as well as interface strengthening in the Al2O3/Ti composites. Furthermore, it was firstly speculated that the TiC could be electrochemically anodized to form an oxide like Ti metal. These characteristics enable Al2O3/Ti/TiC composites as the crack‐healing materials at room temperature. [ABSTRACT FROM AUTHOR]

Investigates the chemical and electrical features of the grain boundaries in polycrystalline ceramics. Formation of an electrostatic potential barriers; Relationship between the defect chemistry and electrical characteristics of the grain boundaries; Effects of process parameters on grain boundary characteristics.

The energy‐harvesting ability of the lead‐free ferroelectric Ba(Zr,Ti)O3 was investigated and greatly enhanced using the Kim novel electrothermodynamic cycle for low‐temperature application. Ba(Zr,Ti)O3 was synthesized with a Zr:Ti ratio of 10:90 (BZT10) by hot‐press sintering, which exhibited a mix relaxor‐ferroelectric behavior. For power generation using the Kim cycle with low and high temperatures of TL = 25°C, TH = 120°C, the most optimized temperature pattern occurred for a heating time of 12.5 s and a cooling time of 22.5 s. Under these conditions, the electric field increased during the novel isodisplacement process, and the displacement variation in the isoelectric step reached the highest value and maximized the BZT10 cycle loop area. Applying these conditions while lowering TL to 20°C, an energy density ND = 504 mJ/cm3 was achieved. This value is the highest obtained energy density in a practical test for lead‐free ferroelectric bulk material in the BaTiO3 family. [ABSTRACT FROM AUTHOR]

The key to miniaturization of piezoelectric devices is to build high‐performance fine‐grained piezoceramics. Although the preparation of fine‐grained ceramics can be achieved by hot press sintering or spark plasma sintering, complex processes, and high costs hinder the popularization of such technologies. In this work, a one‐step conventional pressureless sintering technique based on partially amorphized nano‐precursors has been proposed for low‐cost preparation of submicron‐structured ceramics. Using this technology, 0.36BiScO3–0.64PbTiO3 ceramics with an average particle size of 170 nm and a relative density of 95% can be prepared at temperature as low as 900°C, while the samples still have excellent piezoelectric properties (d33 = 220 pC/N, g33 = 40 × 10−3 Vm/N). In the process of sintering partially amorphized nano‐precursors, the initial densification rate is faster than the grain growth rate, which can be attributed to two effects promoting low temperature densification, one is the liquid phase sintering mechanism associated with the amorphous phase, and the other is the filling effect of small particles deposited at the grain boundaries. This work is simple and easy to implement, and it is expected to be extended to the preparation of other types of fine‐grained ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Al2O3/Ti composites containing 0‐30 vol% dispersed fine Ti particles were fabricated using a hot‐press sintering method at 1500°C from mixtures of Al2O3 and TiH2 powders. During sintering, TiH2 decomposed to form metallic Ti. The effects of the Ti content on the mechanical and electrical properties of the composites were then investigated. No Ti‐Al intermetallic compounds were detected by X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy indicated the presence of Al‐Ti‐O solid solution and Ti‐O phases. The composites showed enhanced densification; the measured densities were higher than the calculated theoretical values. Microstructural observation revealed homogeneously distributed fine Ti particles dispersed in the Al2O3 matrix. The Ti particle size ranged from submicrometer to a few micrometers depending on the Ti content. The fracture mode of the composites was primarily transgranular, in contrast to the intergranular fracture mode of monolithic Al2O3. Although the flexural strength was decreased with increase in Ti content, the composite containing 20 vol% Ti displayed the maximum fracture toughness of 4.3 MPa·cm1/2, which was 37% greater than that of monolithic Al2O3. The composites containing more than 15 vol% Ti exhibited drastic decreases in resistivity (~10−1 Ωcm), which were attributed to the formation of interconnected Ti networks at these Ti contents. The percolation threshold volume for electrical conduction in the present system was calculated to be 13.8 vol%. The results indicate that dispersing fine Ti particles into Al2O3 increased the fracture toughness and improved the conductivity of Al2O3. [ABSTRACT FROM AUTHOR]

The Ce3+-doped Y2O3-Al2O3-SiO2 ( YAS) bulk glasses with low SiO2 (≤40 mol%) were prepared by flame spray-quench method and hot press sintering. YAG nanoglass-ceramics were derived from YAS bulk glass by a controlled crystallization. The differential thermal analysis ( DTA) results showed that the glass-forming ability of YAS system was strongly dependent on SiO2 content and the supercooling degree required for forming YAS glass increased with the decrease of SiO2 content. The YAS glass compositions had been extended to low SiO2 phase region (10-40 mol%) by flame spray-quench method. The study of crystallization process showed that glass matrixes experienced initially a phase-separation followed by crystallization during the heat treatment. The phase-separated grains (100-300 nm) that were composed of YAG nanocrystallites precipitated in the glass matrix. And the intensity of emission spectra increased with the decreasing SiO2 content. [ABSTRACT FROM AUTHOR]

The Ca-doped γ-La2S3 (γ-La2S3:Ca) powders with various La/Ca ratios were prepared using the coprecipitation method. The γ-La2S3:Ca powders with a ratio of La/Ca = 5 was selected for sintering in order to study the effects of hot-pressing temperature and time on the microstructure and optical properties of γ-La2S3:Ca ceramics. The results showed that 1100°C for 1 h were the optimum hot-press parameters, at which the maximum transmittance of γ-La2S3:Ca ceramics up to 40% at 13 μm was obtained. [ABSTRACT FROM AUTHOR]

(K0.5Na0.5)NbO3 (KNN) is a potential lead-free replacement for Pb(Zr, Ti)O3 (PZT) piezoceramics, but its piezoelectric properties are inferior to those of PZT. By growing single crystals of KNN, it may be possible to improve the piezoelectric properties. Recently, single crystals of KNN were grown by the solid-state crystal growth (SSCG) method, but the crystals were very porous. In this paper, a method of growing dense single crystals by SSCG in a hot press will be described. (110)-oriented single seed crystals of KTaO3 were buried in KNN powder, with 0.5 mol% of K4CuNb8O23 added as a sintering aid. After consolidation by uniaxial and isostatic pressing, the tablets were hot pressed in a two-stage treatment. During hot pressing, dense single crystals of KNN grew using the KTaO3 seed crystal as a template. The effect of hot pressing on single crystal growth will be discussed. [ABSTRACT FROM AUTHOR]

The sintering kinetics of a pure magnesium aluminate spinel, MgAl2O4, and that doped with LiF were determined through the use of the master sintering curve technique developed by Su and Johnson. 20 Powders with 0%, 0.5%, and 1.0% by mass LiF were densified in a vacuum hot press under a range of unaxial pressures. After the sintering mechanisms in each temperature and pressure regime were determined, an optimized vacuum hot-pressing schedule was formulated for spinel powders doped with 1.0% by mass of LiF. In addition to forming a transient liquid phase, the presence of LiF leads to the formation of oxygen vacancies that promote late-stage sintering in MgAl2O4. [ABSTRACT FROM AUTHOR]

Cerium monosulfide (CeS) powder was synthesized by the reduction of Ce[sub 2]S[sub 3] powder with metallic Ce, which was obtained from ceria (CeO[sub 2]) powder using carbon disulfide (CS[sub 2]) gas. To obtain the maximum amount of CeS from a mixture of Ce[sub 2]S[sub 3] and Ce, an excess amount of metallic Ce, a stoichiometric composition, was necessary in the synthesis at 1273 K for 10.8 ks. The preliminary sintering experiments also were performed using a synthetic CeS powder containing a small amount of Ce, Ce[sub 2]O[sub 2]S, and β-Ce[sub 2]S[sub 3] as impurities. It was found that the oxygen content in the sintered compact decreases gradually as the sintering temperature increases, because of the removal of the impurities due to the evaporation of the volatile CeO. Single-phase CeS was formed by sintering at 2173 K. To evaluate the activation energy for densification of single-phase CeS, a CeS powder was prepared by milling an initial sintered compact and was used as an ingredient for hot-press experiments. Densification data during hot-press sintering were analyzed using a kinetic equation, showing that boundary diffusion is a rate-limiting process. The results suggest that this boundary diffusion model can explain well the densification data, with an apparent activation energy of 479 kJ·mol[sup -1]. [ABSTRACT FROM AUTHOR]

Using citric acid, ethylene glycol, ZrOCl2·8H2O, HfOCl2·8H2O, TiCl4, NbCl5, and TaCl5 as raw materials, the (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C high‐entropy ceramic precursor was prepared by Pechini coordination polymerization method. The precursor and pyrolysis products were analyzed and characterized by different methods. The results showed that the precursor formed a chelate structure, which greatly improved the stability of the precursor, and was clear and transparent with moderate viscosity (30–50 mPa·s). At a low pyrolysis temperature of 1600°C, single‐phase (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C high‐entropy ceramic nanopowders with a ceramic yield of 50.8% can be obtained. The high‐entropy ceramic powder has high purity, a particle size of about 140–200 nm, and uniform element distribution. It is suitable for introduction into fiber‐reinforced ceramic matrix composite by precursor infiltration and pyrolysis (PIP) process. [ABSTRACT FROM AUTHOR]

Intense visible and near-infrared frequency upconversion and a frequency downconversion photoluminescence have been reported for the first time in Tm3+ and Er3+ co-doped transparent α-Sialon ceramics under 980 nm excitation. The α-Sialon ceramics were prepared by hot-press sintering technique. Intense upconversion bands at 554, 678, 803 nm, and a downconversion band at 1530 nm were observed as a result of the efficient energy transfer between Er3+ and Tm3+ ions. The quadratic dependence of upconversion intensities on the excitation power indicates that the upconversion process is governed by two-photon absorption process. The sintered samples of thickness 0.20 mm have transparency above 80% in the range of 2000 to 4200 nm and it reaches as high as 82% at 3350 nm. Moderately low phonon energy was found with the highest frequency band at 828 cm−1. These novel properties manifest the potential applications of transparent α-Sialon ceramics as a multifunctional material. [ABSTRACT FROM AUTHOR]

Alumina powder with a platelet morphology was hot‐pressed to transparency with preload pressures of 0‐8 MPa, maximum temperatures of 1750‐1825°C, maximum pressures of 2.5‐80 MPa, and isothermal hold times of 1‐7 hours. Optical transmission (in‐line and total), as well as optical losses (backward/forward scattering and absorption), of the hot‐pressed samples were measured and related to the microstructure. Higher hot‐pressing temperatures increase the in‐line transmission. A gray discoloration of the samples (indicative of high absorption) was minimized by heat treating the powder in air prior to hot pressing and reducing the preload pressure. Maximum pressures above/below 10 MPa increased porosity, which decreased in‐line transmission and increased backward/forward scattering. Lower densities at higher pressures are attributed to a pore‐swelling phenomenon. Increasing isothermal hold time decreased porosity, which increased in‐line transmission and reduced backward/forward scattering. Best optical properties with an in‐line transmission of 65.3% at 645 nm (0.8 mm thick) were achieved by hot‐pressing heat‐treated platelet alumina powder with a preload pressure of 0 MPa, maximum temperature of 1800°C, maximum pressure of 10 MPa, and an isothermal hold time of 7 hours. This high in‐line transmission, despite its large grain size (65 µm), is attributed to crystallographic orientation of the platelets during hot pressing. [ABSTRACT FROM AUTHOR]

The cold‐sintering process (CSP) uses a transient low‐temperature solvent, such as water or water with dissolved solutes consistent with the ceramic composition, to achieve functionalization at lower temperatures via the dissolution and precipitation principle. Here, during the CSP, the use of molten NaOH as a flux solvent promoted the rearrangement and precipitation of CaYNbMnO7 particles. CaYNbMnO7 ceramics were successfully obtained at 350°C and under a uniaxial pressure of 700 MPa. The ceramic was not a single‐phase structure but consisted of a cubic‐phase structure and a layered perovskite structure. To verify the high‐temperature thermal stability of CaYNbMnO7 ceramic prepared at 350°C, a comparative study was conducted with conventional sintering (CS). Results indicate that the ceramics obtained by CSP and CS have negative temperature coefficient characteristics. The cold‐sintered ceramic has a wider temperature range and better aging stability. (The minimum value of the aging coefficient is ∼2.49%.) Simultaneously, CSP is beneficial for promoting the linearization of the relationship between the logarithm in the resistivity (lnρ) and the reciprocal for the absolute temperature (1000/T) in the ceramic. However, the CSP has little effect on the material constant B and thermal activation energy Ea of the ceramic, providing a basis for the low‐temperature synthesis of high melting point thermosensitive ceramics. [ABSTRACT FROM AUTHOR]

Tb3Al5O12 (TAG) ceramics with high optical quality were fabricated successfully by a solid‐state reaction method combined with hot isostatic pressing (HIP) post‐treatment. The microstructure, optical transmittance, Verdet constant, and thermo‐optical properties were investigated. The obtained TAG ceramics showed a dense microstructure, and the in‐line transmittance reached 82.8% at 1070 nm after laser‐grade polishing. The Verdet constant of TAG ceramics was measured to be 50.9 rad·T1·m−1 at 1070 nm, which is higher than that of commercial Tb3Ga5O12 crystals. The Faraday isolator based on TAG ceramics can provide an isolation ratio of 30 dB with a laser power of more than 1 kW. With excellent optical quality, high Verdet constant, and maximum working power, TAG transparent ceramics are promising for applications of kilowatt‐level Faraday isolators. [ABSTRACT FROM AUTHOR]

In this report, a facile wet chemical method using acetonitrile combined with thermal annealing was used to prepare Li2S‐P2S5 (LPS) based glass‐ceramic electrolytes with (1 wt%, 3 wt%, and 5 wt% Ce2S3) and without Ce2S3 doping. The crystal structure, ionic conductivity, and chemical stability of Li7P3S11 glass‐ceramic electrolytes were examined at varying temperatures (250–350°C). The results indicated that the highest ionic conductivity of 3.15 × 10−4 S cm−1 for pure Li7P3S11 was observed at a temperature of 325°C. By incorporating 1 wt% Ce2S3 and subjecting it to a heat treatment at 250°C, the glass ceramic electrolyte attained a remarkable ionic conductivity of 7.7 × 10−4 (S cm−1) at 25°C. Furthermore, it exhibited a stable and extensive electrochemical potential range, reaching up to 5 volts when compared to the Li/Li+ reference electrode. By tuning the glass transition and crystallization temperature, cerium doping seems to make Li7P3S11 more chemically stable, compared to its original 70Li2S‐30P2S5 counterpart. According to Raman and X‐ray photoelectron spectroscopy analyses, cerium doping inhibits the decomposition of highly conductive P2S74‐ (pyro‐thiophosphate) to PS43− and P2S64−. Doped LPS has a greater crystallinity and more uniform microstructure than pure LPS, according to XRD, Raman spectroscopy, and scanning electron microscopy analysis. Consequently, Li7P2.9Ce0.1S11 electrolyte shows great potential as a solid‐state electrolyte for constructing high‐performance sulfide‐based all‐solid‐state batteries. [ABSTRACT FROM AUTHOR]

Ni‐based alloys provide good brazing filler characteristics for the many applications of SiC ceramics. Nevertheless, the presence of graphite is unavoidable in the reaction between Ni and SiC, leading to a significant degradation of the mechanical properties of the joint. This study investigates the effect of Mo in Ni–30Si alloy on the brazing of SiC at 1300°C, to regulate interfacial reactions and reduce residual stresses by decreasing overall coefficient of thermal expansion (CTE) values throughout the brazing process. The addition of Mo up to 8 at.% efficiently suppresses graphite accumulation by converting it into Mo2C + Ni3Mo3C phases and lowering the CTE to 5.4 × 10−6/°C. When the Mo loading exceeds 12 at.%, the interactions between the filler and SiC are reduced as a result of the non‐homogeneous dispersion of Mo. The experimental findings indicate that the joint without graphite has a lap shear strength of 107 MPa, which is nearly three times greater than the joint with graphite. Thermodynamic analyses are performed to provide a comprehensive understanding of the underlying mechanisms responsible for the formation of distinct phases in brazed joints. [ABSTRACT FROM AUTHOR]

The reaction between ZrC and iridium powders was studied in the temperature range of 1000–1600°C. The reaction was stated to start at a temperature as low as 1000°C. The only high‐melting intermetallic phase, ZrIr3, was obtained as a substitutional solid solution ZrIr3±δ. A new analytical approach to relating the composition to the lattice parameter of cubic binary substitutional ZrIr3±δ solid solutions was proposed. This approach is based on comparing the distribution by elemental composition and by lattice parameter in a range of ZrIr3±δ solid solutions. This made it possible to determine the lattice parameter of a stoichiometric ZrIr3 phase, a0 = 3.971(5) Å. [ABSTRACT FROM AUTHOR]

Functionally graded ceramics (FGCs), which combine the properties of various composite ceramics, have been widely used in the aerospace, armament, and other industries. One of the newest melt‐growth ceramic additive manufacturing techniques, laser directed energy deposition (LDED), enables the creation of gradient materials by controlling the ratio of powder delivery. Ceramic–ceramic type gradient materials are the subject of fewer studies, and the majority of LDED gradient material systems now in research are metal–metal type and metal–ceramic type gradient materials. In this paper, LDED is used to create TiCp reinforced Al2O3 FGCs with three different transition paths. The results indicate that the longitudinal section of the gradient samples distinctly exhibits characteristics of gradient distribution. Furthermore, as the proportion of TiCp increases, there is a corresponding increase in the proportion of TiCp particles in the samples. The microstructure of Al2O3 transforms from columnar crystals to irregular shapes. Regarding the mechanical properties of the gradient samples, the area containing 30 wt.% of TiCp shows a significant improvement in wear resistance, with a 48.13% increase compared to the Al2O3 region. Additionally, this region demonstrates a 12.62% rise in hardness and a 9.48% increase in fracture toughness. [ABSTRACT FROM AUTHOR]

Multilayer ceramic actuators find extensive utility in applications requiring precise displacement control or force output, due to their advantages of high precision control, rapid response, low driving voltage, low power consumption, and so on. For practical applications, there is a need for high‐performance multilayer ceramic actuators (MLAs) that combine cost‐effectiveness, efficiency, and temperature stability. In this work, 1.5 mol%Sm‐doped 0.25 Pb(Mg1/3Nb2/3)O3–0.36PbZrO3–0.39PbTiO3 piezoelectric ceramics with PbO–CuO as sintering aid were fabricated. The addition of PbO–CuO significantly reduced the sintering temperature by 300°C, while having minimal impact on the piezoelectric properties. The optimized sintering condition, achieved at a low sintering temperature of 950°C with the introduction of a tiny 0.4 wt% sintering aid, yields impressive piezoelectric strain coefficient d33* = 690 pm/V. This substantiates the viability of employing low‐cost Ag/Pd (90/10) as inner electrode, which can be co‐fired with ceramic layer to fabricate MLA. This innovation enables a remarkable displacement of 1 µm at a low driving voltage of 200 V across a 9‐layers piezoelectric actuator, accompanied by high‐temperature stability, exhibiting <20% variation over the temperature range of 30–250°C. These results underscore a great potential for high‐performance piezoelectric actuators over a broad temperature range. [ABSTRACT FROM AUTHOR]

The nacre with brick‐and‐mortar structure enables multiple toughening and strengthening mechanisms, and bioinspired ceramics with brick‐and‐mortar structure have been attracting much attention from many researchers. However, the process of constructing precise and uniform microstructure is quite complicated. Herein, we propose a novel and facial method to fabricate composite ceramics with brick‐and‐mortar structure. Si3N4 microspheres prepared by particle‐stabilized foaming and centrifugal spray drying were directly hot pressed after being immersed in suspension and evenly wrapped with ZrO2. The mechanical properties of composite ceramics were optimized by adjusting the pressure during sintering and ZrO2 content. When ZrO2 content was 10 wt% and sintering pressure was 5 MPa, the fracture toughness of ZrO2/Si3N4 brick‐and‐mortar composite ceramics reached 9.02 MPa·m1/2, and the flexural strength was 784 MPa, which were increased by 46.9% and 26.5%, respectively, compared with the control group. While retaining excellent flexural strength, the strong interface also induces crack to deflect and branch along the two‐phase interface of the brick‐and‐mortar structure caused by the residual stress, which was derived from the mismatch of the thermal expansion coefficient of ZrO2 and Si3N4, consuming more fracture energy to achieve the toughening effect. [ABSTRACT FROM AUTHOR]

As a typical perovskite‐like layered structure (PLS) ceramic, Sr2Nb2O7 (SNO) possesses a high Curie temperature TC value above 1300°C, which is expected to work in higher temperature environment. However, pure SNO presents a piezoelectric constant d33 value of ∼ 1 pC/N. Hence, (Li, Ce) ions are doped in SNO ceramics, which increases the distortion of oxygen octahedrons and enhances the intrinsic contribution of piezoelectric properties. The increased domain size with large proportion of high response areas means that the extrinsic contribution is also improved. The introduction of (Li, Ce) ions can also promote ceramic's grain growth and reduce oxygen vacancies, leading to the improvement of electrical properties. The optimal component Sr1.96(Li, Ce)0.02Nb2O7 ceramics exhibit a d33 value of 3.1 pC/N, a higher resistivity of 1.65×106 Ω·cm at 700°C and an excellent thermal stability (a d33 value of 3.0 pC/N after annealing at 1200°C for 2 h). This work provides an effective approach with simple process and low cost for the application of PLS materials in high‐temperature environments. [ABSTRACT FROM AUTHOR]

PLZT (7.45/71/29) ceramics with fully dense microstructure and high transmittance were fabricated by a hot-press sintering method. The effects of temperature on the phase structure, ferroelectric property, and electric-induced light scattering performance of the PLZT ceramics were examined and analyzed. XRD patterns indicated that the PLZT sample tended to transform from rhombohedral phase to tetragonal phase with the temperature increasing. And the temperature-dependent ferroelectric hysteresis behavior of the PLZT sample revealed the conversion of a saturated square hysteresis loop to a double-loop-like hysteresis loop, accompanied with the significant reduction in coercive field and remnant polarization. Depending on the temperature, the PLZT sample exhibited three different kinds of electric-induced light scattering performance. [ABSTRACT FROM AUTHOR]

Transparent 0.9 Pb( Mg1/3 Nb2/3) O3-0.1 PbTiO3 ( PMN- PT) based ceramics were prepared by a conventional solid-state synthesis without using a hot-press method. The ceramics became transparent when they were sintered in an O2 atmosphere. The optical transmission increased with decreasing diameter of the calcined powder, which was controlled by the size of zirconia ball-milling media. Substitution of 3 mol% La for Pb in PMN- PT further increased the optical transmission to 68% at the wavelength of 2000 nm, which was comparable to that of hot-pressed Pb( Mg1/3 Nb2/3) O3- PbTiO3 based transparent ceramics. [ABSTRACT FROM AUTHOR]

In this article, the reactivity of Ti2AlC powders, with 3 and 10 μm alumina, Al2O3, fibers during pressure-assisted sintering is explored. Samples were fabricated by hot-isostatic-pressing ( HIPed) or hot-pressing ( HPed), and characterized by X-ray diffraction, differential thermal analysis, and electron microscopy-both scanning and transmission-equipped with energy dispersive X-ray spectroscopes. Samples prepared at 1300°C were fully dense, with no apparent reaction between fiber and matrix. In samples HPed to 1500°C, even pure Ti2AlC powders dissociated to Ti3AlC2 according to: 2 Ti2AlC = Ti3AlC2 + TiAl x ( l) + (1- x) Al ( l/ v), with x < 1. More severe Al loss results in the formation of TiC y. The presence of the Al2O3 fibers delayed densification enough to allow most of the Al and some of the Ti to escape into the vacuum of the hot press or react with the encapsulating glass during HIPing a resulting in a more intensive dissociation of the Ti2AlC. Although, in principle Ti2AlC can be reinforced with Al2O3 fibers, the processing/use temperature will have to be kept below 1500°C, as, at that temperature the fibers, used here, sinter together. [ABSTRACT FROM AUTHOR]

High-density MoSi2/Al2O3 ceramic composites were prepared by hot-press sintering using MoSi2 powders and α-Al2O3 powders as starting materials. The mechanical and dielectric properties of these composites were studied. The results showed that both the real part and the imaginary part of the complex permittivity increased with the increasing MoSi2 content over the frequency range of 8.2-12.4 GHz, which means that the dielectric performance of the composites can be adjusted mainly by controlling the MoSi2 content. On the other hand, high strength and high hardness were also obtained in these composites with MoSi2 as the reinforcing phase. These results indicated that the MoSi2/Al2O3 composite was a promising material with both the electromagnetic wave absorbing and the load-bearing abilities. [ABSTRACT FROM AUTHOR]

In order to study the orientation dependence of the electrical properties of layered structure cathode materials used in lithium-ion thin-film microbatteries, a typical composition, LiCoO2, has been hot-press sintered in bulk with a strong crystallographic texture. Microstructural characterization using X-ray diffraction, scanning electron microscopy, and Raman spectroscopy showed that the degree of LiCoO2 texture depended upon the precise hot-press conditions used. There was a pronounced orientation of the polycrystalline LiCoO2 c-axis in the pressing direction with a high Lotgering factor ( f=0.96) for sintering at 950°C. The pronounced texture led to a remarkable anisotropy in electronic conductivity between directions parallel (σ∥) and perpendicular (σ⊥) to the pressing direction in the temperature range 190–400 K, with σ⊥/σ∥=187 at 300 K. The results suggest that texture can be used to tune not only the well-known electrochemical performance of all-solid-state lithium-ion thin-film batteries, but also their electronic conductivity. [ABSTRACT FROM AUTHOR]

Near fully dense ZrO2(3Y)/Fe3Al composites with significantly improved fracture toughness were synthesized by hot-press sintering at 1350° C. High fracture toughness and bending-strength values, 36 Mpa.m1/2 and 1321 MPa, respectively, were achieved in 40 vol% Fe3AI composite ceramics, whereas those same values for ZrO2 (3Y) alone were 10 Mpa.m1/2 and 988 MPa, respectively. Microscopic observation of the crack path revealed that Fe3AI particle uniformly dispersed in the matrix have obvious crack-bridging effect. Improved thermal-shock resistance was also obtained, which was attributed to higher toughness, thermal conductivity, and lower Young's modulus by adding of Fe3Al particles. [ABSTRACT FROM AUTHOR]

Bi3NbTiO9 ceramics were prepared by ordinary firing and by hot-press sintering. The crystal structures of the ceramics were investigated by X-ray diffractometry. Scanning electron microscopy observation showed that the platelike grains were oriented after hot pressing. Dielectric, piezoelectric, and ferroelectric characterizations, as well as the electrical resistivities, showed remarkable anisotropy in the hot-pressed samples. Because of grain orientation in the hot-pressed samples, the remanent polarization and piezoelectric constant in the direction perpendicular to the pressing axis were much higher than in the unoriented, ordinary fired samples. [ABSTRACT FROM AUTHOR]

Cold sintering process (CSP) developed recently has attracted much attention due to the ultralow sintering temperatures and high efficiencies with the assist of transient liquid phase (TLP). Based on CSP, we have further established a protocol for low‐temperature sintering processes by combining TLP with other sintering technologies, including hybrid sintering process with microwave and TLP (MW‐TLP), and hybrid sintering process with spark plasma sintering and TLP (SPS‐TLP). Three typical electro‐ceramics (TiO2, CaWO4, and ZnO) are selected, which are highly densified (>97%) with excellent electrical properties at reduced sintering temperatures, applied pressures or holding times, demonstrating the feasibility of MW‐TLP and SPS‐TLP in fabricating electro‐ceramics. Especially, the Q × f value of TiO2 ceramics (38,020 GHz) prepared by MW‐TLP at 1000°C is 46.2% and 23.4% higher than that of microwave and spark plasma sintered samples, respectively, and comparable to traditional thermal sintered (TTS) samples at 1300–1400°C. The dielectric properties of MW‐TLP CaWO4 ceramics sintered at 900°C for 2 h are comparable to TTS samples sintered at 1000–1300°C for 2–5 h. ZnO ceramics can be highly densified (∼98%) by SPS‐TLP with mild sintering conditions (200–300°C and 3.8–50 MPa) compared to SPS (>500°C) and CSP (>100 MPa). The frameworks of fundamental mechanisms are outlined together with the experimental data. It is expected that this work will provide promising sintering methods to fabricate electro‐ceramics and offer inspirations on sintering combinations to develop low‐temperature sintering processes with high efficiencies. [ABSTRACT FROM AUTHOR]

The influence of crystal anisotropy on the micromechanical properties of ceramic grains plays an important role in the design of the macromechanical performance of bulk polycrystalline samples. To this end, the effect of crystal orientation on fracture toughness and strength was investigated by microcantilever bending experiments combined with finite element method (FEM) simulations in grains of a polycrystalline ZrB2 sample. The sample was prepared by hot pressing and the crystal orientations were determined by electron backscatter diffraction after careful surface preparation. The bending tests were carried out on notched and unnotched microcantilevers cut from specific grains along the prismatic (⊥ to c‐axis), basal (∥ to c‐axis), and intermediate (45° to c‐axis) directions of ZrB2 crystals using focused ion beam milling. The fracture toughness and strength were determined by FEM‐derived analytical solutions. The fracture strength was similar with values of about 11–12 GPa in every direction. Enhanced plasticity was found in the intermediate direction of unnotched beams as compared to the other two brittle orientations. The fracture toughness was found to be 30% higher in the intermediate direction (4.1 MPa m0.5) than those measured for the basal (3.1 MPa m0.5) and prismatic directions (3.3 MPa m0.5). These findings were explained by the orientation dependence of slip system activations which provide a new way in the design of textured polycrystalline ZrB2 ceramics toward enhanced damage tolerance. [ABSTRACT FROM AUTHOR]

Ceramic composites consisting of a silicon carbide matrix and boron carbide particles of various sizes and weight percentages were produced, characterized, and mechanically tested to elucidate the effect of microstructure on the mechanical response. All samples were observed to have flexural strength values lower than either of the constituent phases; however, blends with finer B4C particles (<10 μm) exhibited improved fracture toughness. Residual stresses from the mismatch in thermal expansion of the materials are found to be fundamental to these variations in mechanical response, resulting in either microcracking during processing or producing an initial stress state within the composite prior to testing. Microcracks were observed in samples with larger B4C particles (∼77 μm), causing a significant reduction in mechanical properties, while the finer B4C particles were found to be microcrack free. Residual stress measurements via X‐ray diffraction and Raman spectroscopy show increasing compressive stresses within the SiC matrix as the weight percentage of boron carbide increases, however both flexural strength and fracture toughness are found to decrease, indicating that the boron carbide particles that are in a tensile stress state are an important strength‐limiting feature. This is corroborated by fracture analysis. The results of both characterization and mechanical testing compare well with those predicted by micromechanics models. [ABSTRACT FROM AUTHOR]