Preparation and High-Temperature Stability of (Zr_1/5La_1/5Sm_1/5Dy_1/5Gd_1/5)O_2−x High-Entropy Ceramic Materials

ZrOCl₂·8H₂O, La₂O₃, Sm₂O₃, Dy₂O₃, and Gd₂O₃ powders were used as raw materials to prepare equimolar-ratio (Zr_1/5La_1/5Sm_1/5Dy_1/5Gd_1/5)O_2−x high-entropy ceramic materials via chemical co-precipitation method. Microstructure, phase structure, high-temperature stability, and evolution of phase composition of the powders under high-temperature conditions were studied. Results show that (Zr_1/5La_1/5Sm_1/5Dy_1/5Gd_1/5)O_2−x high-entropy ceramic materials synthesized via chemical co-precipitation method exhibited single cubic fluorite phase structure. After heat treatment at 1400 °C for 5 h, solid solution of monoclinic rare-earth oxide separated from cubic fluorite phase. Ceramic powders exhibited stable monoclinic phase and rare-earth oxide-doped ZrO₂ dual phase after long-term heat treatment up to 100 h. Results of the fitting of x-ray spectroscopy data show that oxygen vacancy content in high-entropy ceramic powders decreased from 85 to 57% after 100 h of heat treatment. Results of thermogravimetry and differential scanning calorimetry measurements show that hydroxides in high-entropy ceramic powders underwent dehydration reactions at 273 and 454 °C, and the separation of rare-earth oxides from cubic solid solutions occurred when the temperature increased above 1320 °C.