Crossover from itinerant to localized states in the thermoelectric oxide [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]

H. Sakabayashi; R. Okazaki

doi:10.1103/PhysRevB.103.125119

paper

Crossover from itinerant to localized states in the thermoelectric oxide [Ca $_{2}$ CoO $_{3}$ ] $_{0.62}$ [CoO $_{2}$ ]

arXiv:2102.13250 · doi:10.1103/PhysRevB.103.125119

Abstract

The layered cobaltite [Ca $_{2}$ CoO $_{3}$ ] $_{0.62}$ [CoO $_{2}$ ], often expressed as the approximate formula Ca $_{3}$ Co $_{4}$ O $_{9}$ , is a promising candidate for efficient oxide thermoelectrics but an origin of its unusual thermoelectric transport is still in debate. Here we investigate \textit{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.

6 pages, 6 figures. Accepted for publication in Phys. Rev. B

Crossover from itinerant to localized states in the thermoelectric oxide [Ca $_{2}$ CoO $_{3}$ ] $_{0.62}$ [CoO $_{2}$ ]

Abstract

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Crossover from itinerant to localized states in the thermoelectric oxide [Ca2​CoO3​]0.62​[CoO2​]

Abstract

References in corpus (7)

Cited by in corpus (5)

Crossover from itinerant to localized states in the thermoelectric oxide [Ca $_{2}$ CoO $_{3}$ ] $_{0.62}$ [CoO $_{2}$ ]