Thermophysical and mechanical properties of dual-phase medium- and high-entropy rare-earth zirconate ceramics

The medium-entropy ceramic (La1/3Nd1/3Gd1/3)2(Zr3/4Ce1/4)2O7 and high-entropy ceramic (La1/5Nd1/5Sm1/5Eu1/5Gd1/5)2(Zr3/4Ce1/4)2O7 were successfully synthesized. The two ceramics had a pyrochlore-fluorite dual-phase structure, and they exhibited excellent phase stability at elevated temperature. Grain refinement or solution strengthening improved the Vickers hardness, fracture toughness and elastic modulus of the dual-phase ceramics. Compared with the single-element ceramic La2Zr2O7, multicomponent doping resulted in a significant increase in the thermal expansion coefficient. Simultaneously, the thermal conductivity of the dual-phase ceramics was lower than that of single-phase ones. In addition, on account of the large size disorder parameter of the medium-entropy ceramic, the thermal conductivity could outperform its high-entropy counterpart. These results indicate that pyrochlore-fluorite dual-phase rare-earth zirconates have enormous potential in applications concerning next generation thermal barrier coatings.