Thermoelectric Properties of High‐Entropy Wolframite Oxide: (CoCuNiFeZn)1−xGaxWO4

Abstract

Herein, the synthesis of high‐entropy wolframite oxide (CoCuNiFeZn)1‐xGaxWO4 through standard solid‐state route followed by spark plasma sintering and their structural, microstructural, and thermoelectric (TE) properties are investigated. X‐ray diffraction pattern followed by patterns matching refinement shows a monoclinic structure with the volume of the unit cell decreasing with increasing Ga content. The optical bandgap for these oxides shows a cocktail effect in high‐entropy configuration. The Seebeck coefficient indicates electrons as dominating charge carriers with a nondegenerate behavior. The electrical resistivity decreases with increasing temperature depicting a semiconducting nature. Thermal conductivity in high‐entropy samples (κ ≈ 2.1 W m−1 K−1 @ 300 K) is significantly lower as compared to MgWO4 (κ ≈ 11.5 W m−1 K−1 @ 300 K), which can be explained by the strong phonon scattering due to large lattice disorder in high‐entropy configuration. The TE figure of merit zT increases with Ga doping via modifying all three TE parameters positively.