Synthesis and thermoelectric properties of the novel A-site deficient Zn0.5Rh2O4 compound

A novel thermoelectric material, A-site-deficient spinel Zn0.5Rh2O4, was prepared by subtracting Li ions from Li0.5Zn0.5Rh2O4 immersed in a K2S2O8 aqueous solution. The electric conductivity (σ) increased 6-fold after extracting Li (σ=8.8 S/cm (Li0.5Zn0.5Rh2O4), 50 S/cm (Zn0.5Rh2O4) at 600 °C), whereas the Seebeck coefficient (S) only slightly increased (S=203 μV/K (Li0.5Zn0.5Rh2O4), 216 μV/K (Zn0.5Rh2O4) at 600 °C). In Zn0.5Rh2O4, a mixed-valence configuration of Rh3+ and Rh4+ at a ratio of 1 to 1 and a half-deficient A-site were realized, resulting in high σ and even slightly increased S, which were likely attributed to the rather high power factor of 2.3×10−4 W/m K2 at 600 °C. Our findings demonstrate that controlling the Rh4+/Rh3+ ratio is a promising method for enhancing the thermoelectric properties.