Ferroelectric materials with a morphotropic phase boundary (MPB) can exhibit enhanced dielectric, piezoelectric, and electrooptic properties, compared with conventional ferroelectric materials. In this paper, dense (1-x)Ba₂NaNb₅O₁₅-x Sr₂KNb₅O₁₅ (BNN-SKN) tungsten bronze structured ceramics of binary solid solution system were obtained by a solid-state sintering method. The microstructure and electric properties of BNN-SKN were investigated to explore the potential MPB regions. The MPB coexisting with Ccm2 and P4bm appears as x=0.7. As the SKN content increases, the phase transition temperature and dielectric constant of the measured samples reach their extreme values as x=0.7, i.e., T_m =170, ε_TR =1 211, and ε_m=3 326. In addition, the ferroelectric properties of BNN-SKN system were also analyzed, and the factors affecting the ferroelectric change in this binary system were discussed.

Single-phase bulk high-entropy spinel ceramics of (Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)Fe₂O₄ were prepared via solid-phase reaction. The phase composition, microstructure and element distribution were analyzed by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The volume density of the ceramics increases and the porosity decreases with the increase of sintering temperature. The dense high-entropy spinel ceramic sintered at 1 200 ℃ presents a single-phase, uniform distribution of elements, and its bending strength and fracture toughness reach 43.00 MPa and 1.30 MPa·m^1/2, respectively. The high-entropy spinel ceramic as a good load bearable broadband microwave absorbing ceramic has dielectric loss and magnetic loss to electromagnetic wave, and the maximum effective absorption bandwidth (EAB=12.37 GHz) maxi can be obtained at 3.0 mm.

Flash sintering is extensively investigated for over a decade since its discovery, but its practical application is seldomly discussed. A primary challenge in utilizing flash sintering is a difficulty in sintering large samples. This is since in a typical direct current (DC) flash sintering, the current is concentrated primarily in the center of the sample, causing a significant temperature gradient between the interior and surface of the sample, thus leading to an inhomogeneous microstructure in the final product and sometimes large stresses in the sample that breaks the material. In this paper, we utilized the alternating current (AC) with varying frequencies to investigate its effect on this inhomogeneity issue in flash sintering. The results indicate that increasing the frequency significantly enhances the uniformity of the sample. The underlying mechanism is related to a significant "skin effect" in AC flash sintering, where the current density is concentrated on the surface of the sample rather than its center, compensating for a higher radiation heat loss at the surface and resulting in a more uniform sample temperature. This work provides a potential approach to enhance the flash sintering for industrial applications.

The macroscopic mechanical response and micro-fracture mechanism of Al₂O₃/SiC composite as a multiphase ceramic under impact loading were investigated. The dynamic strength and strain rate sensitivity were analyzed by load tests methods of one-dimensional stress wave and plane shock wave. The Hugoniot curve of high pressure and local deformation characteristics of material were determined at different stress modes. The results show that the micro-fracture mechanism of the multiphase ceramic differs with the macro-stress characteristics. The macro-deformation of the multiphase ceramic is mainly a brittle failure under impact loading. However, there are some local plastic deformation characteristics on the transcrystalline fracture of large grain and the intergranular fracture of small grain. The SiC particles as a second phase induce crack propagation at grain boundaries and within grains, which plays an important role in the redistribution of impact energy.

A textured SiAlON ceramic with a centripetal grain alignment was obtained via sinter-forging through outer diameter strain ring compression using spark plasma heating. The microstructure, texturing degree and anisotropy of mechanical properties of the ceramic were investigated. The results show that the c-axis (i.e., long axis) of the rod-like SiAlON grains is parallel to the radial direction of the cylindrical sample, forming a centripetal grain alignment. The average included angle between the c-axis and radial direction is 19.2° and 9.9° on the plane perpendicular to pressing direction and parallel to radial direction, respectively. The degree of centripetal texture is 0.79. The hardness on the plane perpendicular to pressing direction is 12% greater than that on the plane perpendicular to radial section, reaching 17.85 GPa. The flexural strength with fracture plane perpendicular to radial section is 57% greater than that with fracture direction parallel to radial direction, which is 1 341 MPa. The fracture toughness with crack propagation perpendicular to radial section is 75% higher than that with crack direction parallel to radial direction, which is 6.27 MPa·m^1/2.

As one of emerging ceramic materials, high-entropy ceramics become a research hotspot in the field of ceramics. However, their compositional design has some challenges for component design based on experimentation and "trial and error". In recent years, the combination of machine learning and experiments can provide an effective method to solve this problem. In this paper, four machine learning models were established, the best-performing gradient-boosting decision tree model (R²=0.92) through training and evaluation was selected for prediction. A single-phase (Ti_0.2V_0.2Zr_0.2Nb_0.2Hf_0.2)N high-entropy nitride ceramic was then synthesized based on the predication by the model. This effective approach can provide some ideas for the design of high-entropy nitride ceramic and discover new systems.

Direct ink writing technology is conducive to molding personalized and customized products with complex structures. However, it is easy to produce pores and an-isotropic problems of mechanical properties when printing a dense solid structure. In this paper, Al₂O₃ was used as a raw material and a nozzle with a diameter of 2.0 mm was selected for direct ink writing. The results show that the layer height is 0.8 mm, the internal structure of the printed sample is relatively dense, and no pores appear after writing. Also, the mechanical properties parallel to/perpendicular to the inter-layer are similar, and the anisotropy index is close to 100%, thus alleviating the anisotropy problem of mechanical properties.

The application of doped HfO₂ ferroelectric thin films in nonvolatile memory devices becomes popular in condensed matter physics and materials science. Recent studies indicate that La doped HfO₂ has excellent ferroelectric properties, and the ferroelectric remanent polarization is 45 μC/cm² as the maximum value reported. Nd doping is expected to enhance the ferroelectric properties of HfO₂ due to its similar chemical properties of Nd and La, but little research has been reported. In this paper, high quality Nd-doped HfO₂ (i.e., Nd∶HfO₂) thin films were grown on La_0.67Sr_0.33MnO₃ (bottom electrode)/SrTiO₃ (001) substrates by using oxide molecular beam epitaxy. According to the results by X-ray diffraction and high-resolution electron microscopy, Nd doping can induce the transition of HfO₂ from a monoclinic phase to an orthorhombic phase. In addition, the results by high resolution electron microscopy also show that Nd∶HfO₂ has a tetragonal phase structure near the interface, connecting (111) crystalline Nd∶HfO₂ and (001) crystalline perovskite oxide substrates. The systematic studies on epitaxial growth and ferroelectric properties of Nd∶HfO₂ films can expand the research of doped HfO₂.

The effect of Er₂O₃ doping on the microstructure and electrical properties of ZnO-Bi₂O₃-Sb₂O₃-Co₂O₃-MnO₂-Cr₂O₃-SiO₂ varistor was investigated. A part of Er is dissolved in the Bi-rich phase as doping Er₂O₃, which has a great influence on the grain boundary characteristics and electrical properties of ZnO varistors. The grain boundary resistivity decreases, the leakage current density increases, the double Schottky grain boundary barrier height and the nonlinear coefficient firstly increase and then decrease, and the breakdown field strength increases with increasing Er₂O₃ content from 0.09% to 0.35% (in mass fraction). The ZnO varistors obtained have a nonlinear coefficient of 54.4±1.5, a breakdown field strength of (470.1±2.8) V·mm^-1, a leakage current density of (1.9±0.1) μA·cm^-2, and a loss tangent of less than 0.03 at Er₂O₃ doping content of 0.27%, showing the optimum comprehensive electrical properties. The standard deviation of the performance parameters is small, indicating that the samples have a good reproducibility. This work provides a reference for the preparation of Er₂O₃-doped ZnO varistor ceramics with the excellent performance.

Cold sintering process (CSP) is an efficient and energy saving sintering method emerging in recent years. In this paper, the (1-x)BNT-xNN dielectric ceramics with the density of more than 97% were prepared by CSP. The effect of CSP parameters and NaNbO₃ content on the density, phase structure, microstructure, and dielectric characteristics of (1-x)BNT-xNN ceramics were investigated. The results show that the CSP can drastically reduce the grain size and prevent some components like Bi and Na from volatilizing due to low sintering temperature and short holding time, thereby increasing the dielectric constant and reducing the dielectric loss. The remnant polarization decreases, and the temperature stability of dielectric constant increases as the content of NaNbO₃ increases. When x=0.3, the variation in dielectric constant of the 0.7BNT-0.3NN ceramic is less than 6% at 25-400 ℃, and the dielectric loss is less than 5%. It is indicated that the (1-x)BNT-xNN ceramics prepared by CSP are one of the promising candidates for the applications in temperature-stability ceramic capacitors.