Marked reduction in the thermal conductivity of (La0.2Gd0.2Y0.2Yb0.2Er0.2)2Zr2O7 high-entropy ceramics by substituting Zr4+ with Ti4+

Abstract

The (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xTix)2O7 (x = 0–0.5) high-entropy ceramics were successfully prepared by a solid state reaction method and their structures and thermo-physical properties were investigated. It was found that the high-entropy ceramics demonstrate pure pyrochlore phase with the composition of x = 0.1–0.5, while (La0.2Gd0.2Y0.2Yb0.2Er0.2)2Zr2O7 shows the defective fluorite structure. The sintered high-entropy ceramics are dense and the grain boundaries are clean. The grain size of high-entropy ceramics increases with the Ti4+ content. The average thermal expansion coefficients of the (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xTix)2O7 high-entropy ceramics range from 10.65 × 10−6 K−1 to 10.84 × 10−6 K−1. Importantly, the substitution of Zr4+ with Ti4+ resulted in a remarkable decrease in thermal conductivity of (La0.2Gd0.2Y0.2Yb0.2Er0.2)2(Zr1-xTix)2O7 high-entropy ceramics. It reduced from 1.66 W m−1 K−1 to 1.20 W m−1 K−1, which should be ascribed to the synergistic effects of mass disorder, size disorder, mixed configuration entropy value and rattlers.