Thermophysical and electrical properties of rare-earth-cerate high-entropy ceramics

A new series of rare-earth-cerate high-entropy ceramics with compositions of (La0.2Nd0.2Sm0.2Gd0.2Dy0.2)(2)Ce2O7 (HEC1), (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)(2)Ce2O7 (HEC2), (La0.2Nd0.2Sm0.2Yb0.2Dy0.2)(2)Ce2O7 (HEC3), (La0.2Nd0.2Yb0.2Gd0.2Dy0.2)(2)Ce2O7 (HEC4), (La0.2Yb0.2Sm0.2Gd0.2Dy0.2)(2)Ce2O7 (HEC5) as well as a single component of Nd2Ce2O7 are fabricated via sintering the corresponding sol-gel-derived powders at 1600 degrees C for 10 h. HEC1-5 samples exhibit a single-cerate phase with fluorite structure and high configurational entropy. Compared with Nd2Ce2O7, HEC1-5 samples have a lower grain growth rate owing to the sluggish diffusion effect. The chemical compositional uniformity of HEC1-5 as well as Nd2Ce2O7 does not apparently change after annealing at 1500 degrees C for different time intervals (1, 6, 12, and 18 h). Compared with 8YSZ, HEC1-5 samples display the decreased thermal conductivity and increased thermal expansion coefficient. The lattice size disorder parameter of HEC1-5 is negatively related to the thermal conductivity in 26-450 degrees C. Furthermore, HEC1-5 and Nd2Ce2O7 exhibit lower oxygen-ion conductivity, meaning an increased resistance to oxygen diffusion.