Perovskite manganites and layered cobaltites: potential materials for thermoelectric applications

Abstract

Metal-transition oxides are potential materials for thermoelectric devices operating at high temperatures (T≫300 K). In particular, compounds exhibiting small resistivity and large Seebeck coefficient are required. Two kinds of oxides have been retained: the ‘misfit’ cobaltites which are p-doped metallic phases and the electron doped perovskite manganites. For the former, it is found that the Ca for Sr substitution enhances the thermopower values in the Pb/Sr/Co/O misfit cobaltite whereas it has only a moderate effect in the case of the Tl/Sr/Co/O phase. From this study, it appears that the oxidation state of Co in the conducting layers plays a crucial role on the physical properties. Moreover, for the manganites, we show that electron-doped SrMnO₃ can be prepared by a two-steps method. The doping, created via substitution at either the A-site (Pr³⁺ for Sr²⁺) or B-site (Mo⁶⁺ for Mn⁴⁺), leads to metallic compounds with large thermopower values.