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

Herein, the synthesis of high-entropy wolframite oxide (CoCuNiFeZn)(1-x)GaxWO(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 (kappa approximate to 2.1 W m(-1) K-1 @ 300 K) is significantly lower as compared to MgWO4 (kappa approximate to 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.

Automated summary

In this study, high-entropy wolframite oxide (CoCuNiFeZn)(1-x)GaxWO(4) was synthesized through a solid-state route followed by spark plasma sintering, and their structural, microstructural, and thermoelectric properties were investigated. The results showed a monoclinic structure with a decreasing unit cell volume as the Ga content increased. The optical bandgap exhibited a cocktail effect in the high-entropy configuration. The dominant charge carriers were found to be electrons with a nondegenerate behavior based on the Seebeck coefficient. The electrical resistivity decreased with increasing temperature, indicating a semiconducting nature. The thermal conductivity of the high-entropy samples was significantly lower compared to MgWO4, which can be attributed to the strong phonon scattering caused by the large lattice disorder in the high-entropy configuration. Ga doping positively modified all three thermoelectric parameters, resulting in an increase in the thermoelectric figure of merit (zT).