Compounds of rare earth zirconates with pyrochlore structure are candidates for the application of thermal barrier coatings of next generation. In order to modify the mechanic properties and maintain the low thermal conductivity, other trivalent rare-earth element substitution is commonly used. Presently, investigation on the evaluation of the property of thermal expansion is attracting more attention. In this paper, a feature parameter of thermal expansion coefficient at high temperature (α_∞) was proposed by combining Grüneisen’s equation and the Debye heat capacity model. Using α_∞ model, the thermal expansion property of different compounds can be easily figured out by first principles. Firstly, α_∞ of ZrO₂, HfO₂, were calculated, and results are in good agreement with the experimental data from the literature. Moreover, α_∞ of La₂Zr₂O₇, Pr₂Zr₂O₇, Gd₂Zr₂O₇, and Dy₂Zr₂O₇ were calculated, and results demonstrated that the model of α_∞ is a useful tool to predict the thermal expansion coefficient at high temperature. Finally, Gd₂Zr₂O₇ with 4 different Yb dopant concentrations (Gd_1-xYb_x)₂Zr₂O₇ (x = 0, 0.125, 0.3125, 0.5) were calculated. Comparing with the experimental data from the literature, the calculation results showed the same tendency with the increasing of Yb concentration.

In the preparation processes of aluminum oxynitride (AlON) powders by carbothermal reduction and nitridation, the homogeneity of mixed raw powders between Al₂O₃ and C is a critical factor by which the final composition and related properties of AlON transparent ceramic will be decided. In this paper, a silane coupling agent was used as a dispersant to optimize the distribution uniformity of raw material of Al₂O₃ and C, and the preparation of AlON powder with controllable composition and its distribution is investigated. The results show that the silane dispersant could effectively improve the distribution uniformity of raw material. The silane coupling agent contains functional groups of −SiH₃ and −C_nH_2n+1O. XPS showed that the silane could react with C and Al₂O₃ to form the Si–C bond and C–Al₂O₃ bond, respectively. The silane coupling agent provides a connected bridge for raw material powders. When the amount of the silane was 5 wt%, the mixed powder had a great distribution uniformity. The addition of silane coupling agent improved the reactivity of raw materials and decreased the synthesis temperature of AlON. The single-phase AlON powder was obtained after the Al₂O₃/C mixed powder was kept at 1670 °C for 30 min. Furthermore, the grain size of AlON powder was 100–200 nm with an AlN content of 27.5 mol%. With the increase of holding time to 4 h, the grain size increased to 15 μm, indicating that sintering between particles occurred, which may reduce the sintering activity of the powder.

In this study, the Gd₂Zr₂O₇-based ceramic target was densified via pressureless sintering which follows well with Kingery’s three-stage sintering theory. Sintering temperature is the key factor affecting the densification of targets. In the initial stage, when the sintering temperature is in the range of 1200–1450 °C, the porosity decreases with the density of targets slowly increasing to 64.71%. Grain boundary diffusion controls the densification process. In the middle stage, at 1450–1500 °C, the density ratio of the target rapidly rises to 77.6%. The competition between grain boundary migration rate and pore shrinkage rate leads to the maximum isolated porosity. In the final stage, when the sintering temperature is above 1500 °C, the density ratio of the target significantly increases to 97.28% at the temperature of 1600 °C. Even when the holding time is extended to 7 h at 1500 °C, the density ratio of the target only reaches 85.72%. With the increase in sintering temperature and prolongation of holding time, the fracture toughness of the ceramic targets exhibited a trend of initial increase followed by a decrease. Density ratio and grain size were identified as key factors influencing fracture toughness. When the density ratio reached approximately 80%, the fracture toughness achieved its maximum value of 2.245 MPa·m^0.5. When the sintering temperature exceeds 1450 °C, both the Young’s modulus and hardness of the targets increase rapidly, which significantly enhances their fracture toughness. However, with the increase in sintering temperature or holding time, the grain grows rapidly. This excessive grain growth reduces grain boundary.