Thermoelectric properties of rhodates: Layeredβ−SrRh2O4and spinelZnRh2O4

Density functional calculations are used to obtain the electronic structure of $\beta \text{−}{\mathrm{SrRh}}_2{\mathrm{O}}_4$ in comparison with spinel ${\mathrm{ZnRh}}_2{\mathrm{O}}_4$. Both materials are band insulators, with substantial crystal field induced band gaps, reflecting strong transition-metal–O hybridization. However, due to the bonding topology in these materials, the valence bands are very narrow. This leads to high thermopowers within standard Boltzmann transport theory, and indicates that they can be the basis of good thermoelectric materials provided that they can be doped into metallic states with reasonable carrier mobility. In the case of $\beta \text{−}{\mathrm{SrRh}}_2{\mathrm{O}}_4$, scattering due to Sr disorder is important. Also, again in $\beta \text{−}{\mathrm{SrRh}}_2{\mathrm{O}}_4$, the band gap may be large enough to be of interest for photoelectrochemical ${\mathrm{H}}_2$ production.