Journal of the American Ceramic Society最新文献

Introducing the concept of high entropy in functional materials is a promising way to improve the stability, but the mechanism of its influence has rarely been discussed in detail. In this work, (CoCrFeMnNi)₃O₄ spinel films were prepared by the alloy oxidation method. The effect of sputtering power on the structure, electrical properties, and electrical stability of films was investigated. The results showed that the increase of ion energy during sputtering promotes grain growth resulting in the decrease of resistivity. The selective oxidation and kinetically controlled oxidation during oxidation process caused the gradient distribution of Cr³⁺, which affected the sluggish diffusion effect and further lead to the better electrical stability of the films. Notably, the fastest Cr³⁺ diffusion rate had the highest disorder of the Cr³⁺ distribution in the 30 W films, whose resistivity drift rate under accelerated aging at 125°C for 400 h is reduced from 9.67% to 1.05%. This work provided a research case for improving the electrical stability of manganese-based spinel films by the sluggish diffusion effect and the scientific basis for high stability electronic devices fabrication.

All phase diagram and thermodynamic property data of unary rare-earth sesquioxides (RE₂O₃) in literature have been critically evaluated to obtain a consistent set of thermodynamic data for all six stable and metastable phases (C, B, A, H, X, and L) of RE₂O₃. In the evaluation, systematic energetic trends of RE₂O₃ depending on ionic radius of RE and the extrapolated data from RE₂O₃ containing binary systems were taken into account to obtain more accurate thermodynamic property data and phase transition data. Based on the newly established Gibbs energies of unary RE₂O₃ phases, the CALPHAD-type thermodynamic modeling was carried out for inter RE₂O₃ binary systems to obtain the thermodynamic models with optimized model parameters of all solid and liquid solutions, which can successfully reproduce all available and reliable experimental phase diagram data of the binary RE₂O₃–RE′₂O₃ systems. Using thermodynamic models with established model parameters, a complete phase diagram set of all 136 binary RE₂O₃–RE′₂O₃ systems were predicted for the first time. The models with established parameters can be readily expanded to any ternary and high order rare oxide systems for the phase diagram and thermodynamic property calculations.

The mixed rare earth/alkali earth was initially employed to enhance the thermionic emission performance of lanthanum hexaboride (LaB₆) through forming the high-dense (La_1-x-yPr_xBa_y)B₆ polycrystal by spark plasma sintering (SPS). La_0.6Pr_0.3Ba_0.1B₆ exhibits the highest current density in space charge limited (SCL) region at T = 1873K while La_0.5Ba_0.5B₆ has the highest current density in temperature limited (TL) region. The maximum current density of 14.07 A/cm² at T = 1673K for La_0.5Ba_0.5B₆ is higher than that of 11.71 A/cm² at T = 1873K for LaB₆ polycrystal, presenting superior emission characteristics at the low temperature, mainly ascribed to the contribution of the Ba element. With the increase in the Ba content, the location of the highest electron emission shifts from the grain boundary (in La_0.5Pr_0.5B₆ and La_0.6Pr_0.3Ba_0.1B₆) to the internal grain (in La_0.6Pr_0.1Ba_0.3B₆ and La_0.5Ba_0.5B₆). The consumption rate of the elements during thermionic emission follows the order:  Ba > Pr > La. The experimental data on the current density aligns closely with the theoretical predictions, demonstrating the emission of (La_1-x-yPr_xBa_y)B₆ ceramic obeys classical thermionic emission mechanism of metals.

To improve the working temperature of gas turbines, thermal barrier coatings (TBCs) to replace the meta-stable Y₂O₃ partially stabilized ZrO₂ have been explored for decades. Rare earth zirconates (RE₂Zr₂O₇) are regarded as an excellent candidate for next-generation thermal barrier coatings. However, the low fracture toughness of rare earth zirconates is the main hindrance, while the rare earth aluminates (REAlO₃) can be imported into the system to toughen the zirconates. In this work, we introduced multiple rare earth elements to explore the effects of configurational entropy on the mechanical and thermal properties of REAlO₃-RE₂Zr₂O₇ composites. When the high entropy REAlO₃-RE₂Zr₂O₇ composites with 3, 4, and 5 rare earth elements on A site were successfully synthesized, the phases of zirconates and aluminates were kept and the rare earth elements were distributed uniformly. We found that the increase in configurational entropy profoundly improved the fracture toughness of the composites by the entropy effect. The fracture toughness of HE-RAO-RZO-5 reached 3.81 ± 0.66 MPam^1/2 measured by the single-edge notched beam (SENB) method, exceeding the fracture toughness given by the mixing rule by ∼18%, which is among the best values of new TBC materials. Meanwhile, the coefficient of thermal expansion can be tuned by the compositions and the hardness, Young's modulus and thermal conductivity of the composites remained almost unchanged. As a result, we proved that the introduction of configurational entropy could be an excellent method to improve the fracture toughness and tailor the thermal properties of REAlO₃-RE₂Zr₂O₇ composites.

High-temperature sintering is essential for the densification of garnet-type solid electrolytes to achieve high ion conductivity and suppression of Li-dendrite growth. In this study, the densification and electrochemical performance of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZT) electrolyte was optimized by controlling the oxygen content of the atmosphere during sintering. Electrochemical tests were performed on sintered and densified pellets at oxygen contents between 0.005 and 99.995 vol.% using a gassing approach. The relative density and critical current density were optimized to 97.6% and 1.0 mA/cm², respectively, at a high oxygen content. As oxygen content increased, sintered pellets exhibited increased lithium-oxide content by inhibiting Li-loss, facilitating densification. These results are expected to promote the implementation of high-quality LLZT electrolyte and solid-state batteries by exploiting the role of oxygen content during sintering. This study shows that high-quality manufacturing can be achieved with low-cost, pressureless sintering.

The application of compositionally complex carbides under extreme conditions has garnered significant attention. The phase diagram compositionally complex transition metal carbide (Ta_0.2Nb_0.2Hf_0.2Zr_0.2V_0.2)C for synthesis under high-pressure and high-temperature has been systematically investigated for the first time, and a pressure-induced decrease in the compositionally complex carbides phase formation temperature was observed. The asymptotic Vickers hardness and bulk modulus of (Ta_0.2Nb_0.2Hf_0.2Zr_0.2V_0.2)C reached 24.0 GPa and 311.3 GPa. The bulk modulus demonstrates an approximate 30% improvement compared to the average values of individual carbides, indicating that it possesses relatively competitive mechanical properties within the compositionally complex carbides group. The Claperon equation has been utilized to predict the lattice contraction of compositionally complex carbides during phase formation, and the physical mechanism of the high-pressure strengthening has been proposed accordingly. In summary, the research of pressure–temperature phase diagram and the high-pressure strengthening mechanism lay a valuable theoretical basis for the structural design and performance optimization of novel compositionally complex carbides.

This study presents the development of a groundbreaking acetone gas sensor leveraging Cl-doped ZnO nanodisks, designed to operate efficiently at low temperatures. Through comprehensive experimental and theoretical analyses, they have elucidated the exceptional sensing capabilities of Cl-doped ZnO nanodisks. Both undoped and Cl-doped ZnO with varying chlorine concentrations were synthesized on Si/SiO₂ substrates using a straightforward thermal evaporation method in a tube furnace. Notably, the morphology of pure ZnO formed microdisks, whereas the Cl-doped ZnO transitioned to nanodisks, and with increased Cl doping, it further evolved into nanoplates. X-ray diffraction and x-ray photoelectron spectroscopy (XPS) confirmed the successful substitution of oxygen ions with chlorine ions. Enhanced photoluminescence and XPS analyses revealed that Cl-doped ZnO contained a significantly higher density of oxygen vacancies compared to undoped ZnO. The Cl-doped ZnO sensor exhibited an outstanding sensitivity of approximately 40 and an impressive selectivity of 55% toward 100 ppm acetone at 80°C. Cl doping markedly improved the sensor's response and recovery times, enabling the detection of acetone at concentrations as low as 225 ppb at 80°C—a remarkable achievement unattainable with pure ZnO. All characterization results strongly indicate that oxygen vacancies play a pivotal role in enhancing the gas-sensing performance of Cl-doped ZnO nanodisks. Cutting-edge density functional theory calculations uncovered significant interactions between acetone and Cl-doped ZnO through charge density variations and band structure analysis. These interactions resulted in notable changes in the density of states, including a distinct peak near −3 eV, indicating enhanced sensitivity.

An asymmetrically structured sodium cobaltite–calcium cobaltite ceramic composite with enhanced texture was synthesized using co-electrospinning of nanoribbons and rapid thermal processing (RTP). Long-term stability tests revealed that embedding the unstable sodium cobaltite in the chemically more stable calcium cobaltite effectively shields it from degradation at high temperatures in air. The composite has overall impressive thermoelectric properties. Measured at 1073 K, the composite showed an electrical conductivity of 183 S cm⁻¹, a Seebeck coefficient of 233 µV K⁻¹, and heat conductivity of 2.2 W m⁻¹ K⁻¹. It features a high power factor of 9.9 µW cm⁻¹ K⁻² and a figure-of-merit of 0.49, significantly surpassing the thermoelectric performance of sodium cobaltite–calcium cobaltite ceramic composites from previous studies.

Owing to their outstanding performances significantly superior to that of the low- and medium-entropy counterparts, high-entropy diborides attracted extensive attention. Nevertheless, the rising configuration entropy of high-entropy diborides rendered not only the better performances but also the greater formation difficulty due to the strengthened sluggish-diffusion effect. Herein, high-entropy (Hf_0.167Zr_0.167Ti_0.167Ta_0.167Nb_0.167V_0.167)B₂, as the first reported six-principal-component high-entropy IVB–VB transition-metal diborides, was successfully synthesized by a microwave and molten-salt co-assisted thermal-reduction method, under the temperature conditions (1400°C/20 min) remarkably milder than that required by the conventional method for synthesizing high-entropy diborides. More importantly, the as-synthesized high-entropy diboride powders exhibited high composition uniformity, single-crystalline nature and hexagon-platelet-like morphology. Furthermore, the high microwave absorption performance of high-entropy (Hf_0.167Zr_0.167Ti_0.167Ta_0.167Nb_0.167V_0.167)B₂ was demonstrated to be favorable for enhancing its synthesis and self-assembly by producing a unique micro-zone hot-spot effect. This research was predicted to promote the development of synthetic technique and dramatically expand the membership of high-entropy materials.

LiTa₂PO₈ (LTPO) is a novel inorganic ceramic electrolyte that has garnered significant attention due to its high ionic conductivity. However, in all-solid-state battery systems, the tantalum (Ta) within the crystal structure of this electrolyte is prone to reduction by lithium at the anode, resulting in the conversion of Ta⁵⁺ to Ta³⁺ and Ta²⁺. This reduction induces instability in both the structural integrity and performance of the electrolyte, thereby adversely affecting the cycling performance of solid-state batteries. To improve the stability of the crystal structure, large-radius scandium (Sc³⁺) ions were introduced into LTPO. The results demonstrate that Sc³⁺ ions can effectively replace some of the Ta⁵⁺ sites within the structure, thereby altering the crystal framework and increasing the unit cell volume. The incorporation of Sc³⁺ ions not only promotes the growth of LTPO crystals but also enhances grain connectivity. This modification expands the pathways for lithium-ion transport, thereby significantly enhancing the room temperature ionic conductivity of LTPO. The synthesized Li_1.08Ta_1.96Sc_0.04PO₈ exhibits an impressive ionic conductivity of 5.12 × 10⁴ S/cm. Furthermore, lithium symmetric cells fabricated from Li_1.08Ta_1.96Sc_0.04PO₈ demonstrate exceptional cycling stability, underscoring the potential of this doped material for practical applications in energy storage systems.