Journal of the American Ceramic Society最新文献

Solid solution modulation is an ideal method for combining the advantages of different parent compounds while mitigating their disadvantages. Here, we investigated the thermal sensitivity, magnetic properties, and microwave absorption of Mg_xMn_1−xAl_2xFe_2(1−x)O₄ (0.2 ≤ x ≤ 0.8) spinel solid solution ceramics for application in multifunctional devices. The electrical transport and magnetic properties can be modulated by adjusting the solution ratio. The ceramics exhibit negative temperature coefficient characteristic. The B-values from 5065–8056 K, suggesting accurate temperature measurements over a wide temperature range. As a type of soft magnetic material, it has a narrow hysteresis loop and high resistivity. Vector network analyzer studies indicate Mg_0.2Mn_0.8Al_0.4Fe_1.6O₄ could be a candidate for microwave absorption in S-band. This study successfully extends the applicability of Mg_xMn_1−xAl_2xFe_2(1−x)O₄ ceramics for high-temperature thermistors and also confirms potential for multifunctional device.

As the major hydration product of cement, hydrated calcium silicate (C-S-H) governs the overall performance of cement-based materials. The molar ratio of CaO to SiO₂ (Ca/Si ratio) significantly affects the structure and properties of C-S-H. This study analyzed the effect of Ca/Si ratios (0.83–2.0) on the structural morphology evolution, bond lengths and angles, polymerization process, and nanoporosity of amorphous C-S-H, with the help of the ReaxFF force field. The results showed that the reacted C-S-H tend to form a fibrous network-like morphology at low Ca/Si ratios, while the silicate chains are prone to accumulating at high Ca/Si ratios, forming a dense granular ovoid structure. Meanwhile, the Ca/Si ratio has no effect on the bond lengths and angles. In addition, the Ca²⁺ ions can interrupt the silicate chains during hydration, which leads to a decrease in the average silicate chain length with increasing Ca/Si ratio. The porosity of C-S-H decreases from 59.3% to 54.3% when the Ca/Si ratio increases from 0.83 to 2.0. It can be deduced from these findings that the increase in the Ca/Si ratio decreases the compressive strength of cement-based materials but increases their durability.

1–3 piezoelectric composites are widely used in piezoelectric ultrasonic transducers due to their high thickness electromechanical coupling factor. However, the applications of the composites in high-temperature fields are limited by the low heat resistance of both the piezoelectric and polymer phases. To tackle this, we designed and fabricated the BiScO₃–PbTiO₃/epoxy high-temperature 1–3 piezoelectric composites. These composites exhibit a high thickness electromechanical coupling factor k_t of 63%, a large piezoelectric coefficient d₃₃ of 470 pC/N, and a pure thickness vibration mode. Furthermore, we fabricated a high-temperature transducer based on the BiScO₃–PbTiO₃/epoxy 1–3 composites. The bandwidths of the composites measured in water and silicone oil (30% and 23%, respectively) are approximately 1.65 times greater than those of monolithic piezoelectric ceramics (18% and 14%, respectively). The bandwidth of the transducer can be increased to 78% by adding a porous alumina backing layer, with the working temperature reaching up to 300°C. The results indicate that the BS–PT/epoxy 1–3 composite is a potential candidate for high-temperature transducer applications.

Strain engineering is a powerful technique for controlling the performance of semiconductor ceramic systems. In this article, the effect of strain engineering, specifically biaxial compressive and tensile strains, on the bonding characteristics, structure, electronic, and optical properties of nonplanar phosphorene-like (NPP) ZnS ceramic nanolayers was investigated using density functional theory. It was observed that this ceramic exhibits greater stability under significant tensile strains. The structural stability of NPP-ZnS ceramic, both with and without biaxial strain, was confirmed by its negative formation energy. Biaxial strain strongly influences the electronic band structure of NPP-ZnS ceramic nanolayers, leading to a transformation from a direct band gap to an indirect gap under tensile strain. Additionally, the bandgap decreases under compressive strain, while it slightly increases under tensile strain. Various optical properties, including refractive index, extinction coefficient, absorption, reflectivity, optical conductivity, and optical susceptibility, were calculated. Biaxial compressive and tensile strains alter the optical properties, shifting them to higher or lower frequencies. NPP-ZnS ceramic nanolayers exhibit high optical absorption in the UV range, which can be further enhanced by biaxial strain. Furthermore, under increasing compressive strain, the absorption edge moves toward higher energies. This improvement in optical absorption expands the potential applications of NPP-ZnS ceramic nanolayers in optoelectronic devices.

SiC_f/SiC composites have emerged as one of the most promising materials for aero-engine hot-end structures. However, their performance is limited by their susceptibility to oxidation and corrosion reactions with oxygen and water vapor. To overcome this challenge, antioxidant-modified phases are introduced into matrices of SiC_f/SiC composites which improve their water and oxygen resistance. In this study, the resistance of SiC_f/SiC composites modified by yttrium silicate matrix (SiC_f/SiC-YS composites) to air at 1000–1400°C and water-oxygen environments at 1200°C was investigated. The diffusion paths of oxygen in SiC_f/SiC-YS composites and the antioxidant behavior of the yttrium silicate matrix were discussed. Additionally, the differences in oxygen and water-oxygen corrosion resistance of SiC_f/SiC-YS composites at the same temperature were compared. The strength retention of SiC_f/SiC-YS composites after oxidation and water-oxygen corrosion at 1200°C were 138.6% and 108.8%, respectively. This indicates that the addition of water vapor accelerated the degradation of SiC_f/SiC-YS composites. By comparing with SiC_f/SiC composites, it can be concluded that the modification of the yttrium silicate matrix considerably improved the oxidation resistance of SiC_f/SiC composites.

Sr₂Nb₂O₇ (SNO) ceramics are promising high-temperature piezoelectric materials due to their high Curie temperature (T_C), good thermal stability, and high electrical resistivity. However, SNO presents low piezoelectric activity (d₃₃ < 1 pC/N). Here, we successfully obtain textured SNO ceramics with an orientation factor of 0.86 by microstructure regulation. Saturated polarization-electric loop was obtained in textured ceramic with remanent polarization P_r∼3.56 µC/cm² and coercive field E_C∼53.4 kV/cm. The piezoelectric coefficient d₃₃ of the textured SNO ceramics is increased to 3.2 pC/N, with a high T_C of 1342°C, while the low-textured SNO ceramics exhibit no effective d₃₃. Meanwhile, the piezoelectric coefficient d₃₃ of textured SNO ceramics maintains consistency even at 1300°C, showing excellent thermal stability. The underlying mechanism driving this improvement is elucidated, emphasizing the facilitated domain-wall motion enabled by the engineered microstructure. Furthermore, textured SNO ceramics exhibit high resistivity of 1.33 × 10⁶ Ω⋅cm at 800°C. This study presents a simple and feasible microstructure engineering approach to enhance the piezoelectric properties of layer-structured materials, offering valuable insights into the design and development of ceramics for diverse applications.

Incorporating specific defects into complex oxides facilitates the exploration of exotic phenomena and novel functionalities based on the intricate coupling between the defects and lattice/charge. However, methods for maximizing the density of specific defects while enhancing the desired properties have been rarely explored. In this study, the effect of N⁺ ion bombardment-driven specific defects on the properties of bismuth ferrite (BFO) thin films was investigated. Furthermore, atomic structure characterization and computational processing revealed the displacement and orientation of the Fe atoms, which are linearly related to the degree of polarization. The ion bombardment introduced deep-level trap states within the lattice, leading to a significant reduction in the leakage current and improved insulation performance of the films. By precisely engineering the defect content through N⁺ ion bombardment, the pure BFO thin films with remarkable and stable ferroelectric properties (remnant polarization, P_r = ∼116.8 µC·cm⁻²; leakage current, J = ∼1.5 × 10⁻⁸ A·cm⁻²) were fabricated. This innovative defect engineering-based approach enables the customization and optimization of local ferroelectric order parameters, thereby establishing a solid foundation for designing functionalities across various functional material systems.

Toward expanding the application of fly ash in cement-based materials, this study proposes a comprehensive study on predicting the elastic properties of low-volume fly ash concrete, with the replacement levels limited to 30% or less. Unlike conventional ordinary Portland cement concrete, the inclusion of fly ash in concrete brings alterations in properties from both chemical and physical perspectives: (1) the presence of fly ash liberates the alkaline solution that consumes calcium hydroxide to generate secondary calcium silicate hydrate gels; (2) unreacted fly ash particles exhibits a refinement effect on the micropore structure and contributes to forming a denser solid matrix. In order to characterize these effects on the mechanical properties of fly ash concrete, this paper conducts qualitative assessment of hydration reactions and quantitative calculations of volumetric compounds in the material. Utilizing the Mori‒Tanaka scheme, a predictive model is then developed to integrate the hierarchical effects of constituents at multiple scales on the modulus of elasticity of low-volume fly ash concrete. The reliability of the proposed model is validated through a series of mechanical tests involving various mix designs, as well as comparison with other published test data.

Compositional screening is an important strategy to improve the oxidation resistance of high-entropy diborides (HEB₂), yet the related studies are limited. Here, we report a rare-earth (RE) element compositional screening strategy to improve the oxidation resistance of HEB₂. To be specific, the single-phase (Hf_0.28Zr_0.28Ta_0.28RE_0.16)B₂ (HEB₂-RE) samples with 12 different RE elements are fabricated via ultrafast ultrahigh-temperature synthesis and spark plasma sintering techniques, and their oxidation resistance is explored by isothermal oxidation tests. The results show that the as-obtained HEB₂-Sc samples possess the best oxidation resistance among all the as-fabricated HEB₂-RE samples. Such outstanding oxidation resistance is ascribed to the enhanced viscosity of the generated B₂O₃ glass originating from the solid solution of (Zr, Me)_0.84Sc_0.16O₂ complex oxides, as confirmed by transmission electron microscope observations and first-principles calculations.

The system BaO–TiO₂ is technically important because it contains multiple dielectric and ferroelectric phases, including the important BaTiO₃, which is one of the most widely studied dielectric perovskites owing to its dual piezoelectric and ferroelectric properties. The present work revises the subsolidus phase equilibria data by synthesizing previous phase equilibria data and new experimental results using high-temperature (600°–1300°C) and long-term (≤336 h) equilibration, coupled with analytical work based principally on room-temperature X-ray diffraction. The resultant phase diagram is given in both mole and weight percents, extending from the liquidus surface (not investigated) to absolute zero temperature (for inclusion of the previously excluded crystallographic and ferroelectric phase transformations). The major features include (1) correction of four eutectoid and three peritectoid reactions and corresponding temperatures, (2) indication of inferred partial solid solubilities, (3) clarification of the BaTiO₃ solid solubility homogeneity regions, and (4) specification of some invariant point compositions on the liquidus surface.