Transport Properties of Misfit-Layered Cobalt Oxide [Sr_2O_<2-δ>]_<0.53>CoO_2(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We report on the measurements and analyses of resistivity, Hall coefficient, and thermopower of the misfit-layered compound, [Sr_2O_<2-δ>]_pCoO_2, using single-crystalline samples obtained by a high-pressure technique. Using a polycrystalline sample, magnetic susceptibilities are measured to roughly characterize the electronic states of the cobalt ions. The misfit ratio, p, was determined to be 0.53 from transmission electron microscopic analyses. [Sr_2O_<2-δ>]_<0.53>CoO_2 shows metallic conduction down to 2K and Curie-Weiss-like susceptibility as Na_<0.75>CoO_2 does. In addition, the thermopower at room temperature is the smallest among the known misfit-layered cobalt oxides, though the carrier concentration is almost the same as that of the misfit-layered compound, Ca_3Co_4O_9, which has a much larger thermopower. We discuss the room-temperature thermopower in misfit-layered cobalt oxides from the viewpoint of incommensurability-induced anisotropy which changes the density of states near the Fermi level.
社団法人日本物理学会の論文
2006-10-15