Estimation of Gr\"uneisen parameter of high-entropy-alloy-type functional materials

In functional materials like 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 mechanisms. In the first part of this article, we briefly review investigations on lattice anharmonicity in functional materials by Gr\"uneisen parameter ({\gamma}G). One can find that the {\gamma}G can be a good scale for large lattice anharmonicity and for detecting a change in anharmonicity amplitude in functional materials. Then, we show original results on estimation of {\gamma}G for recently-developed high-entropy-alloy-type (HEA-type) functional materials with a layered structure and a NaCl-type structure. As a common trend between those two systems with two- and three-dimensional structures, we find that {\gamma}G increases by a slight increase in configurational entropy of mixing ({\Delta}Smix), and then {\gamma}G decreases with increasing {\Delta}Smix in high-entropy region.