Thermoelectric properties of high-entropy wolframite oxide. (CoCuNiFeZn)${}_{1-x}$Ga${}_x$WO${}_4$

Herein, the synthesis of high-entropy wolframite oxide (CoCuNiFeZn)${}_{1-x}$Ga${}_x$WO${}_4$ 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 MgWO${}_4$ (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. (© 2023 The Authors. physica status solidi (RRL) Rapid Research Letters published by Wiley‐VCH GmbH)