Estimation of the Grüneisen Parameter of High-Entropy Alloy-Type Functional Materials: The Cases of REO_0.7F_0.3BiS₂ and MTe

Abstract

In functional materials such as thermoelectric materials and superconductors, the interplay between functionality, electronic structure, and phonon characteristics is one of the key factors to improve functionality and to understand the underlying mechanisms. In the first part of this article, we briefly review investigations on lattice anharmonicity in functional materials on the basis of the Grüneisen parameter (γG). We show that γG can be a good index for large lattice anharmonicity and for detecting a change in anharmonicity amplitude in functional materials. Then, we show original results on the estimation of γG for recently developed high-entropy alloy-type (HEA-type) functional materials with a layered structure and a NaCl-type structure. As a common trend for those two systems with two- and three-dimensional structures, we found that γG increased with a slight increase in the configurational entropy of mixing (ΔSmix) and then decreased with increasing ΔSmix in the high-entropy region.

Keywords

• Grüneisen parameter
• lattice anharmonicity
• high-entropy alloy
• superconductors
• thermoelectric materials