Preparation and properties of (Ce 0.2 Zr 0.2 Ti 0.2 Sn 0.2 Y 0.2-x Ca x )O 2-δ (x=0∼0.2) high-entropy of compositionally-complex ceramics

In this paper, a series of (Ce 0.2 Zr 0.2 Ti 0.2 Sn 0.2 Y 0.2-x Ca x )O 2-δ ( x  = 0∼0.2) high-entropy of compositionally-complex ceramics were prepared using solid-state reaction method. The results showed that the content of Ca 2+ had significant effects on the phase composition, microstructure and properties of the prepared materials. As Ca 2+ content increased, single-phase fluorite was easier to form. When x  ≤ 0.05, materials contained dual-phase of fluorite and pyrochlore structures. When x  ≥ 0.075, the prepared materials showed single-phase fluorite structure, which indicated that high-entropy fluorite ceramics (HEFCs) could be prepared under this condition. When Ca 2+ content increased from 0.075 to 0.2, grain size of HEFCs decreased, and relative density decreased from 95.7 % to 78.6 %. Thermal conductivity of these HEFCs varied from 1.87 W m −1  K −1 to 1.60 W m −1  K −1, which was lower than 8YSZ. As Ca 2+ content increased, both size disorder and mass disorder increased too leading to low thermal conductivity. The results indicate that the prepared HEFCs are promising for thermal insulation applications.