Enhanced thermoelectric properties in a layered rhodium oxide with a trigonal symmetry

We have synthesized an original layered rhodium oxide in the Bi-Sr-Rh-O system with alternately stacked conductive $\mathrm{Rh}{\mathrm{O}}_{x}$ layer and insulating $({\mathrm{Bi}}_{0.75}{\mathrm{Sr}}_{0.25}){\mathrm{O}}_{1.5}$ fluorite-type layers. Thermopower, resistivity, Hall coefficient, magnetoresistance, and magnetization measurements evidence high thermoelectric properties with Pauli-like paramagnetism and large carrier concentration $(\ensuremath{\sim}{10}^{22}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3})$. The room-temperature resistivity, thermopower, and power factor are $1.6\phantom{\rule{0.3em}{0ex}}\mathrm{m}\ensuremath{\Omega}\phantom{\rule{0.2em}{0ex}}\mathrm{cm}$, $63\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{V}∕\mathrm{K}$, and $2.48\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{W}∕\mathrm{cm}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{2}$, respectively, which are comparable with those of the best existing $p$-type thermoelectric oxides, the misfit-layered cobalt oxides with the hexagonal $\mathrm{Cd}{\mathrm{I}}_{2}$-type $\mathrm{Co}{\mathrm{O}}_{2}$ layer. In these crystals, the temperature dependence of the resistivity and the magnetic susceptibility suggest the presence of strong electron-electron interaction. This two-dimensional material emphasizes the potential of the transition-metal oxides for thermoelectric applications.