High-temperature Ceramics Research Articles

High-temperature piezoelectric properties and thermal stability of BF-BT-based ceramics by double A-site ion modification

This paper investigates 0.69BiFeO3-0.31BaTiO3+x(0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3) (abbreviated as 0.69BF-0.31BT+x(0.8BNT-0.2BKT) (0≤x≤0.025) quaternary high-temperature lead-free piezoelectric ceramics. X-ray diffraction(XRD) analysis reveals that these ceramics exhibit morphotropic phase boundaries (MPB) with coexistence of rhombohedral (R) and pseudo-cubic (Pc) phases. The in-situ d33 measurements indicate that 0.69BF-0.31BT+x(0.8BNT-0.2BKT) possesses excellent thermal stability, achieving an in-situ d33 of 687 pC/N at Tdr = 382℃, and a high Curie temperature (Tc = 474℃). Transmission electron microscopy (TEM) results show that the high depolarization temperature (Tdr) and excellent piezoelectric properties are attributed to compositional inhomogeneity introduced by the incorporation of double relaxation ferroelectrics (0.8BNT-0.2BKT), resulting in the formation of polar nanoregions (PNRs). This design demonstrates that the quaternary system of BF-BT+(BNT-BKT)-based ceramics serves as a promising example for optimizing high-temperature lead-free piezoelectric ceramics.

Achieving outstanding comprehensive performance with high piezoelectricity in CaBi2Nb2O9-based high-temperature piezoelectric ceramics via multi-field coupling strategy

Achieving outstanding comprehensive performance with high piezoelectricity in CaBi2Nb2O9-based high-temperature piezoelectric ceramics via multi-field coupling strategy

Simultaneously Achieved High Piezoelectricity and High Resistivity in Na0.5Bi4.5Ti4O15-Based Ceramics with High Curie Temperature.

Good piezoelectricity and high resistivity are prerequisites for high-temperature acceleration sensors to function correctly in high-temperature environments. Bismuth layered structure ferroelectrics (BLSFs) are promising candidates for piezoelectric ceramics with excellent piezoelectric performance at high temperatures, high electrical resistivity, and high Curie temperatures (Tc). In this study, (LiMn)5+ is substituted for Bi at the A-site, and Ce-doping is performed to replace Ti ions in Na0.5Bi4.5Ti4O15, which achieves the desired combination of high piezoelectric coefficients and high resistivity. Herein, we prepared Na0.5Bi3(LiMn)0.9Ti4-xCexO15 high-temperature piezoelectric ceramics, achieving a high piezoelectric coefficient d33 of 32.0 pC/N and a high resistivity ρ of 1.2 × 108 Ω·cm (at 500 °C), and a high Curie temperature of 648 °C. It is important that the d33 variation remains within 8% over a wide temperature range from 25 °C to 600 °C, demonstrating excellent thermal stability. Structural characterization and microstructure analysis showed that the excellent piezoelectric coefficient and high resistivity of cerium-doped Na0.5Bi4.5Ti4O15-based ceramics are attributable to the synergistic effects of structural characteristics, defect concentration, refined grain size and domain morphology. This study demonstrates that the superior properties of Na0.5Bi3(LiMn)0.9Ti4-xCexO15 ceramics are crucial for the stable operation of high-temperature accelerometer sensors and for the development of high-temperature devices.

Low hysteresis in composites ceramics achieved by building polarization field and restoring force

Large strain hysteresis and remnant strain are one of the vital reasons for the absence of BiFeO3-BaTiO3-based ceramics in commercial actuator fields. Here, we elaborately propose a strategy, preparing 0–3 type composite ceramics, to reduce the hysteresis and remnant strain, and the target is successfully achieved by building restoring force and polarization field. Normal strain constant and electric field-induced strain in 0–3 composites have enhanced by 260% and 196% compared to those of non-composite ceramics, respectively. Also, hysteresis and remnant strain in 0–3 composites have decreased by 35.9% and 50.6% in contrast to those of non-composites. Superior electrostrain properties under the low electric field are attributed to the construction of polarization field, restoring force, and micro-capacitance, coinciding with phase field simulation, and the strategy will pave a useful way to optimize the hysteresis and remnant strain in BiFeO3-BaTiO3-based high-temperature ceramics.

Deciphering the piezoelectric and conductive mechanisms of Nb-doped Bi3Ti1.5W0.5O9 high-temperature piezoelectric ceramics

The study utilizes Bi3Ti(1.5-x)NbxW0.5O9 (BTW-xNb, x=0.00, 0.01, 0.02, 0.04, 0.06) bismuth layered piezoelectric ceramics synthesized via a conventional solid-phase reaction process. This is the study to investigate the impact of B-site Nb ion doping on the structural and electrical properties of BTW-xNb ceramic. The results show that all ceramics have a single bismuth layer structure, with reduced lattice distortion according to Rietveld refinement findings. The presence of oxygen vacancies in the ceramic is the main factor that affects the high temperature conductivity of the samples. The XPS results, the increase in the activation energy of AC and DC conductivity confirm that doping with Nb5+ ions reduces oxygen vacancy concentration. The ceramics with the highest overall electrical performance are the BTW-0.02 Nb ceramics. Notably, the DC resistivity at 500 °C was enhanced from 9.16 × 105 Ω·cm (x = 0.00) to 8.24 × 106 Ω·cm. The TC was enhanced from 730 °C(undoped) to 743 °C. At 500 °C, tanδ decreases from 21.1 % to 8.2 %. The ceramic's increased resistivity increases the polarization voltage, resulting in more complete polarization. The d33 is increased from 7.5 pC/N (undoped) to 13 pC/N. Furthermore, the piezoelectric properties remain stable up to 700°C, suggesting that the material has considerable potential for use at elevated temperatures.

Synergistic regulation of Nd2O3 doping and components accommodation to attain enhanced electrical performance in BiScO3-PbTiO3 high temperature ceramics

Nd2O3-modified BiScO3-PbTiO3 (Nd: BS-PT) ceramics were synthesized with the aim of augmenting the piezoelectric response. A comprehensive investigation was conducted to explore the impact of Nd and PT content on the structure, microstructure, and electrical properties of Nd: BS-PT ceramics. The introduction of Nd ions resulted in notable enhancements in the piezoelectric and dielectric properties of BS-PT ceramics. In the case of 0.02Nd: BS-0.64PT, the piezoelectric coefficient (d33) reached an impressive 550 pC/N. Furthermore, the room-temperature dielectric constants exhibited a continuous increase with rising Nd content. The relaxation behavior demonstrated a progressive augmentation corresponding to the increased Nd content. Conversely, both saturation polarization and remnant polarization exhibited a gradual decline with increasing Nd content. These variations are attributed to the refined microstructure and enhanced relaxation behavior induced by Nd doping. This innovative Nd: BS-PT ceramic demonstrates that judicious incorporation of Nd can markedly enhance the piezoelectric properties of BS-PT ceramics. Such a modification significantly augments the performance of BS-PT ceramics across various applications, notably in sensors and actuators.

Mechanical properties and multi-field ferroelastic response of Nb/Mn Co-doped CaBi4Ti4O15 high-temperature ferroelectric ceramics

CaBi4Ti4O15 (CBT) ceramics are promising piezoelectric materials that have been widely studied for high-temperature applications. Despite significant advancements in the electrical performance of CBT ceramics, the understanding of their mechanical behaviors remains limited, which is unfavorable for designing ceramics with high stability and reliability during high-temperature service. This work investigated the mechanical properties and fracture behaviors of Nb/Mn co-doped CaBi4Ti4O15 (CBTNM) with various doping levels, focusing on stress-strain responses and ferroelastic deformation behaviors under uniaxial compression and multi-field coupling conditions. HRTEM analysis reveals small-scale layered domain wall structures on the surface of plate-like grains. The fracture and compressive strengths of CBTNM ceramics initially decrease and then increase with an increase in doping content, and the underlying mechanisms are related to grain size, defects, and densification. CBTNM ceramics exhibit nonlinear stress-strain responses due to ferroelastic deformation under compressive loading, and the resultant irreversible domain switching strain increases with an increase in doping content, while poling can further increase the residual strain. Under multi-field loading conditions, CBTNM ceramics undergo more ferroelastic deformation events and exhibit larger residual strain. The micro-cracks, pores, complicated fracture modes, and degraded fracture surfaces with fragmental and rough features are mainly responsible for the lower elastic modulus and inferior mechanical response. This work enhances our understanding of the mechanical behaviors of high-temperature piezoelectric ceramics and provides guidance for designing high-performance piezoelectric materials for complex environmental applications.

High piezoelectricity and thermal stability of Ce-doped CaBi2Nb2O9-based high-temperature ceramics

As the industry advances at a swift pace, the demand for piezoelectric materials that exhibit both exceptional piezoelectric properties and excellent thermal stability is on the rise. However, it remains a significant challenge to achieve a balance between high piezoelectricity and thermal stability in these materials. In this study, the phase structure, microstructure, and thermal stability of Ce-doped CaBi2Nb2O9 (CLBBN-xCe) high-temperature bismuth layer-structured piezoceramics are studied. It is revealed that the CLBBN-0.1Ce ceramics stand out with a piezoelectric coefficient d33 of 21.7 pC/N and a high Curie temperature of 907 °C. Furthermore, in situ temperature measurement demonstrates that the d33 has a change rate of 20.8 % from room temperature to 400 °C. We found that grain size refinement and domain morphology contribute to excellent electrical properties of the Ce-doped CaBi2Nb2O9-based ceramics. The superior performance of these ceramics suggests they hold great promise for high-temperature applications.

Modeling of the Phase Equilibria in the La<sub>2</sub>O<sub>3</sub>–SrO–ZrO<sub>2</sub> System Using the NUCLEA Database

The goal of this study was to examine the phase equilibria in the La2O3–SrO–ZrO2 system, which is promising as a base for the development of high-temperature ceramics and materials with unique optical, electrochemical, and catalytic properties. Thermodynamic modeling of the phase equilibria in the system under consideration was carried out using the NUCLEA database and the GEMINI2 Gibbs energy minimizer. As a result, thirteen isothermal and one polythermal sections of the phase diagram of the La2O3–SrO–ZrO2 system were calculated in the temperature range 600-3023 K. The obtained data on the phase equilibria in the La2O3–SrO–ZrO2 system were discussed in comparison with the known information for the corresponding binary systems. The phase relations in the system under study were shown to correlate completely with the presence of the phases present in the corresponding binary systems. Temperature changes in the phase relations and boundaries of single-phase, two-phase, and three-phase regions in the system under study were considered. Four ternary eutectic points were identified at the temperatures equal to 2039 K, 2105 K, 2120 K, and 2351 K.

Surface Reconstruction of La0.5Sr0.5CoO3-δ Ceramic toward High Solar Selectivity for High-Temperature Air-Stable Solar-Thermal Conversion.

As a key device for solar energy conversion, solar absorbers play a critical role in improving the operating temperature of concentrated solar power (CSP) systems. However, solar absorbers with high spectral selectivity and good thermal stability at high temperatures in air are still scarce. This study presents a novel surface reconstruction strategy to improve the spectral selectivity of La0.5Sr0.5CoO3-δ (LSC5) for enhanced CSP application. The strategy could efficiently enhance the solar absorptance due to the existence of a high-absorption thin layer composed of nanoparticles on the LSC5 surface. Meanwhile, the crystal facet with low emittance on the LSC5 surface was exposed. Thus, the LSC5 that underwent surface reconstruction achieved a higher solar absorptance (∼0.75) and lower infrared emittance (∼0.19) compared to the original LSC5 (0.63/0.21), representing an improvement of nearly 32%. Additionally, the surface reconstructed LSC5 demonstrated a lower infrared thermographic temperature and a higher solar-thermal conversion equilibrium temperature compared to those of LSC5 and SiC. Moreover, the reconstructed LSC5 could maintain stable performance up to 800 °C in air, which might simplify the complexity of the CSP systems. The surface reconstruction strategy provided a new method to optimize the spectral selectivity of high-temperature stable ceramics, contributing to advancements in solar energy conversion technologies.

Extremely low loss and high electrical resistivity in CaBi2Nb2O9 high-temperature piezoelectric ceramic by adding WO3

An appropriate amount of WO3 was added into CaBi2Nb2O9 high-temperature piezoelectric ceramics to improve the dense microstructure and enhance the electrical properties. A portion of W ions can be incorporated into the lattice, resulting in an increase in the lattice distortion and spontaneous polarization. As a result, the ferroelectric and piezoelectric properties of the ceramics are promoted. Additionally, reducing the concentration of oxygen vacancies can increase the resistivity of ceramics and significantly reduce the dielectric loss. The CBNO-0.375 wt% WO3 sample shows a large piezoelectric coefficient of 17.1 pC/N, a high remnant polarization of 12.60 µC/cm2, a high TC of 951°C and a large electrical resistivity of 1.86 × 106 Ω·cm at 600 °C. Moreover, the dielectric loss at 600 °C maintains a low value of 0.0076, which is one to two orders of magnitude lower than that of CBNO-based ceramics. Therefore, the method of adding WO3 to construct a CBNO ceramic provides a new strategy for high-temperature piezoelectric applications.

Unusual negative thermal expansion of inter-cluster –C–BC–C– bond in carbon rich boron carbide observed using in situ x-ray diffraction technique

Temperature dependent bonding behavior plays a significant role in deciding properties of high temperature ceramics like boron carbide. However, few studies to date have addressed the physical properties of this class of materials with respect to their temperature dependent bonding nature. In addition, materials with the flexibility to accommodate variations in interatomic bonding and lattice vibrations over a wide range of temperatures are less known. In this work, temperature dependent structural analyses of carbon-rich boron carbide microflakes using in situ powder x-ray diffraction techniques (up to 1000 °C) supported by transmission electron microscopy measurements reveal that while most bonds in the rhombohedral structure increase in length with temperature; there is no change in certain bond lengths. However, there is an unusual decrease in length (∼1.03%) of the inter-cluster –C–(central boron)BC–C– without any polyhedral redistribution. This is accompanied by an increase in lattice vibrations without significant alteration to the crystal structure over the wide temperature range studied. Temperature dependent micro-Raman experiments further confirmed the above observations. The above bonding behavior could be directly correlated to the trends in reported results of high temperature conductivity via the model of hole hopping through specific atomic positions of the rhombohedral framework, thus opening the scope to investigate structure–property relationships in high temperature functional materials.

Restraining quenching-induced decline of resistivity in NBT-BFO ceramics by incorporation of BiAlO3

(1-x)Na0.5Bi0.5TiO3-xBiFeO3 (NBT-BFO) is a system with a composition-induced transition from relaxor to ferroelectric. Upon quenching, 0.4NBT-0.6BFO obtain a Td of 640 °C and d33 of 56 pC/N. However, the quenching treatment also causes the reduction of resistivity, which is unfavorable for high-temperature piezoelectric ceramics. The aim of this study is to restrain quenching-induced decline of resistance in NBT-BFO ceramics by doping a small amount of BiAlO3 (BA). For unquenched NBT-BFO-BA, with increasing BA content, the piezoelectric coefficient (d33) decreases slightly, while the resistivity increases. After quenching, both d33 and the depolarization temperature (Td) increase, but more importantly, the resistivity of quenched NBT-BFO-BA is comparable with that of the unquenched samples. This phenomenon is not observed in other quenched samples, and the reason is attributed to the defect dipoles caused by BA. Besides, the enhanced piezoelectric properties and the resistivity can be retained after annealing the quenched samples at 400 °C for 4 h. Thus, this work implies the potential application of NBT-BFO based piezoelectric ceramics at elevated temperatures.

Machinability improvement in micro milling AlN after laser chemical milling

Processing microchannels inside laminated aluminum nitride high-temperature co-fired ceramics (AlN HTCC) packaging, a typical difficult-to-cut ceramic, can effectively solve the heat-dissipation problem of integrated chips used in smart skin. In order to improve the processing efficiency and quality of AlN, the machinability of AlN after laser chemical milling (LCM) was studied through the milling force, machined surface quality, surface defects, formation mechanism, and tool wear. This study established a milling force model that can predict the milling forces of AlN and analyses the reasons for the improvements in the milling force based on experimental data and predicted data. The results from the model and experiments demonstrated that the milling force of the laser chemical milling assisted micro milling (LCAMM) decreased by 85%–90% and 85%–95%, respectively, due to the amount of removal of a single edge was more uniform and the actual inclination angle increased during the cutting process in LCAMM. Moreover, the machined surface quality improved by 65%–76% after LCM because of less tool wear, fewer downward-propagating cracks generated during each feed, and the surface removal mode transformed from intergranular fracture to transgranular fracture, which effectively reducing tool wear and improving tool life. Finally, when feed per tooth and depth of cut were 0.4 μm/z and 5 μm, the optimal machined surface quality was obtained, with a roughness of 64.6 nm Therefore, milling after LCM can improve the machinability of AlN and providing a feasibility for the high-quality and efficient machining of microchannels.

Synergistic design strategy for enhancing the piezoelectric performance of BiFeO3-Based high-temperature piezoelectric ceramics

A novel synergistic strategy was used to improve the piezoelectric characteristics of high-temperature piezoelectric ceramics. This work combined three commonly used strategies, constructing the Morphotropic Phase Boundary to reduce energy barriers, changing domain structures impacting macroscopic piezoelectric properties, and adjusting BO6 octahedral distortions reflecting microstructural changes, thus effectively regulating the piezoelectric behaviors of BiFeO3-based ceramics. As a result, the 0.67BiFeO3-0.32BaTiO3-0.01BiAlO3 component, exhibiting the maximum distortion of the BO6 octahedron and the coexistence of macrodomains and nanodomains, achieved the optimal piezoelectric characteristics (d33 = 225 ± 10 pC N−1, TC = 450 °C). Additionally, the ceramic maintained its high piezoelectric properties even at temperatures as high as 280 °C (346 pC N−1). This study presents a novel collaborative design strategy that combines phase structure, domain structure, and BO6 octahedral distortion, significantly enhancing the development potential of lead-free high-temperature piezoelectric materials in the future.

High-Entropy CeNbO4+δ-Based Ceramics with Ultrahigh Comprehensive Thermosensitive Performances.

Next-generation advanced high-temperature sensors rely heavily on negative temperature coefficient thermosensitive ceramics with low cost, small volume, high sensitivity, and fast response. However, thus far, the enormous challenge of achieving ultrahigh stability and accuracy has become a critical bottleneck restricting the development of thermosensitive ceramics in high-temperature sensor applications. Here, we propose a high-entropy strategy to design a "cation valence self-equilibrium" system in CeNbO4+δ-based ceramics introducing redox couple compensation and ultrahigh density dislocations to solve the problem of temperature-dependent oxygen nonstoichiometry that restricts the performances of high-temperature thermosensitive ceramics. Ferroelastic domains are generated by enhancing the configurational entropy at both A and B sites, resulting in a dramatic increase of dislocation density to >1010 mm-2, which ultimately optimizes the thermosensitive performances. Extreme temperature measurement accuracy with R2 as high as 999.98‰ and RSS as low as 0.011 and high-temperature stability with ΔR/R0 as low as 0.23% after aging at 873 K for 1000 h are realized in high-entropy CeNbO4+δ-based ceramics, indicating a breakthrough in the comprehensive performances of thermosensitive ceramics. This work opens up an effective way to design thermosensitive materials with ultrahigh comprehensive performance to meet the requirements of advanced high-temperature sensors.

LiNbO3-induced phase structure evolution and improved piezoelectric properties in BiFeO3–BaTiO3 ceramics

Eco-friendly (0.73-x)Bi1.05FeO3-xLiNbO3-0.27BaTiO3 ternary ceramics were designed and prepared via a solid-state sintering route. Based on the X-ray diffraction results and Rietveld refinement, it was found that the structure of the ceramics transformed from rhombohedral to tetragonal symmetry with the addition of LiNbO3, and at x = 0.003, there existed a morphotropic phase boundary separating the two phases. Near the phase boundary, the largest values were achieved for the piezoelectric constant d33 and planar electromechanical coupling coefficient kp, being 180 pC/N and 0.27, respectively. Due to the addition of LiNbO3, the grain size tended to become smaller. Additionally, the ceramics were transitioned from normal to relaxor ferroelectrics with increasing x. Despite the fact that the LiNbO3 addition would result in a gradual decrease of Curie temperature, a relatively high Curie temperature (535 °C) was still maintained at x = 0.003, the phase boundary composition, which also showed good temperature stability of piezoelectric properties. These experimental results can provide a reference for the practical applications of high-temperature lead-free ceramics.

Surface Heating Calculation of Composite Material Under the Influence of an Electron Beam on the Surface

Introduction. Modern plasma magnetic confinement systems use tungsten as a material in contact with plasma. Under the influence of high-density plasma irradiation, tungsten undergoes cracking, intense erosion, and macro-particle emission. High-temperature ceramics are considered a promising material for protective coating of plasma components, as they are resistant to thermal loads. One possible solution could be a boron carbide coating, which has a high melting temperature.Materials and Methods. The impact of an electron beam on samples of rolled tungsten and boron carbide and tungsten composite was studied in experiments on the BETA setup. The heat from the beam propagates into the samples, with the maximum temperature reached at the center and decreasing towards the edges. The modeling area represents a cross-section of the samples, optimal for a task with a cylindrical coordinate system. The numerical implementation is based on the correction scheme and the marching method.Results. A new model of heating the boron carbide and tungsten composite sample under the influence of surface heating by an electron beam is presented. The model is based on solving the heat conduction equation in an axially symmetric setup with constant values of specific heat capacity, density, and thermal conductivity of metals.Discussion and Conclusions. An analysis of the model of heating the composite material under the influence of surface heating by an electron beam at constant values of density, thermal conductivity, and specific heat capacity has been conducted. The modeling results are in demand for analyzing experimental results and planning experiments at the Beam of Electrons for Materials Test Applications (BETA) facility, created at the Budker Institute of Nuclear Physics SB RAS.

Thermal-flow characteristics analysis of a novel resilient capacity ceramic insulated winding dry type transformer

With the increasing demand for the resilient capacity of transformers in high-proportion renewable energy grids, the overload capacity of transformers and the thermal conductivity of winding insulation materials have been put forward as important requirements. In response to these requirements, a novel ceramic high temperature tolerance insulation winding is proposed in this paper and is applied in a ceramic insulated winding transformer. A combination of simulation and experimentation is used to analyze the thermal-flow characteristics of this transformer. The temperature and flow field distribution characteristics of transformers with both winding insulation methods (ceramic and Nomex paper) are compared. The internal mechanism of reflux near the iron core and high voltage winding under forced air cooling is clarified. A superior outside cooling condition is obtained. A prototype ceramic insulated winding transformer is developed and tested to verify the accuracy of the simulation model. The results show that the hotspot temperature of the ceramic insulated winding transformer under natural cooling is 10.7% lower than that of the Nomex paper insulated winding transformer. With forced air cooling of 2, 3, 4, 5, and 6 m/s applied at the bottom, the hotspot temperature of the ceramic insulated winding transformer is 11.4%, 10.5%, 9.7%, 14.0%, and 17.8% lower than that of the Nomex paper insulation winding transformer, respectively. Under forced air cooling, a reflux phenomenon is observed in both transformers in the vicinity of the iron core and high voltage winding due to the formation of adverse pressure gradient region and wall viscous force blocking. The strength of the reflux is affected by the magnitude of the forced air cooling flow velocity and the construction of the transformer. The optimal range of the external cooling flow velocity for the ceramic insulated winding transformer is 3–4 m/s. The errors between the simulated temperature and the measured temperature at the nine monitoring points of the prototype are all less than 5%, which verifies the effectiveness of the simulation model. The experimental and theoretical basis for the design and application of resilient capacity dry type transformers is provided by this research.

Ceramic Material Properties in High-Temperature Environments: Recent Trends in Finite Element Analysis Research

The finite element method is commonly utilized for high-temperature ceramics, such as cutting tools, thermal/environmental barrier coatings, and aerospace applications. Cutting performance is influenced by both internal and external factors, including heat transfer, and cutting speed. Friction coefficients and heat transfer issues reveal limitations on cutting tool efficiency, requiring accurate modeling and validation. Although oxide formation and crack failure for barrier coatings are discussed, ceramic materials and geometry must be studied. Extensive research on the nucleation and propagation of micro-crack is needed for next-generation spacecraft component applications by validating the established model based on experimental observation. Modeling and verification research improves ceramic reliability under more stress conditions.