Preparation and properties of (Ce0.2Zr0.2Ti0.2Sn0.2Y0.2-xCax)O2-δ (x=0-0.2) high-entropy of compositionally-complex ceramics

In this paper, a series of (Ce0.2Zr0.2Ti0.2Sn0.2Y0.2-xCax)O2-delta (x = 0-0.2) high-entropy of compositionally-complex ceramics were prepared using solid-state reaction method. The results showed that the content of Ca2+ had significant effects on the phase composition, microstructure and properties of the prepared materials. As Ca2+ 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 Ca2+ 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 Ca2+ 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.