Ultrafine-grained high-entropy zirconates with superior mechanical and thermal properties

Ultrafine-grained (Sm0.2Gd0.2Dy0.2Er0.2Yb0.2)2Zr2O7 high-entropy zirconates with single fluorite structure have been fabricated by high-pressure sintering of the self-synthesized nanopowders for the first time. The as-sintered samples exhibit a good microstructure with a grain size of 220 nm and a relative density of 96.8%, which yield excellent comprehensive mechanical properties with a high Vickers hardness of 12.5 GPa and a high fracture toughness of 3.4 MPa·m1/2. In addition, the as-sintered samples possess a good thermostability with the grain growth rate of 30 nm/h, and a low thermal conductivity of 1.57 W·m−1·°C−1 at room temperature. The superior mechanical and thermal properties are primarily attributed to the “high-entropy” and grain-refinement effects and good interface bonding.