2023 年 131 巻 8 号 p. 343-349
We introduce new approaches to break the trade-off relationship between thermopower (S) and electronic conductivity (σ) in thermoelectric oxide materials by using artificially designed thin-film heterostructures. The output electric power generated by thermoelectric conversion is characterized by power factor (PF = S2 × σ) but PF takes a maximum at a certain carrier concentration, which is restricted by the electron-diffusion model of transport theory. Here, we employ transition metal oxides of LaTiO3 and LaNiO3 to demonstrate two approaches to break the trade-off relationship. One is to introduce compressive strain in LaTiO3 film to control a Mott insulator state to a massive electron metallic state, allowing improved S and σ, giving rise to a 102-times enhancement of PF. Second one is to confine massive electrons and enhance phonon-drag effect in ultra-thin LaNiO3 film sandwiched between wider bandgap LaAlO3 capping layer and substrate with assistance of phonon-leaking effect, leading to a 10-fold increase of S. The present approaches open up new avenues for developing high-performance thermoelectric oxide materials beyond the conventional electron-diffusion theory.
