Recent aspects of oxide thermoelectric materials for power generation from mid-to-high temperature heat source

Rapid progress in thermoelectric performance of oxide materials has been conducted virtually exclusively in Japan, resulting in more than 10 times increase in the ZT values of oxides within the last two decades. This has caused a revolutionary change in the guiding principles of thermoelectric materials research, in which oxide materials had been disregarded as a potential candidate until early 1990s. Promising oxide thermoelectric materials having been discovered include CaMnO₃-based perovskites, Al-doped ZnO, layered cobalt oxides represented by NaCo₂O₄ and Ca ₃Co₄O₉, and SrTiO₃-related phases. This paper reviews the current aspects of oxide thermoelectric materials, and some strategies of nanostructure control for selective reduction of the lattice thermal conductivity (selective phonon scattering) in bulk oxide ceramics will also be discussed.