Crossover from itinerant to localized states in the thermoelectric oxide [Ca2CoO3](0.62)[CoO2]

Article

关键词: THERMOPOWER;    CRYSTAL;    RESISTIVITY;   

DOI  :  10.1103/PhysRevB.103.125119

来源: SCIE

【 摘 要 】

The layered cobaltite [Ca2CoO3](0.62)[CoO2], often expressed as the approximate formula Ca3Co4O9, is a promising candidate for efficient oxide thermoelectrics, but an origin of its unusual thermoelectric transport is still in debate. Here we investigate in-plane anisotropy of the transport properties in a broad temperature range to examine the detailed conduction mechanism. The in-plane anisotropy between a and b axes is clearly observed both in the resistivity and the thermopower, which is qualitatively understood with a simple band structure of the triangular lattice of Co ions derived from the angle-resolved photoemission spectroscopy experiments. On the other hand, at high temperatures the anisotropy becomes smaller and the resistivity shows a temperature-independent behavior, both of which indicate a hopping conduction of localized carriers. Thus, the present observations reveal a crossover from low-temperature itinerant to high-temperature localized states, signifying both characters for the enhanced thermopower.

【 授权许可】

Free