Abstract
We report on the measurements and analyses of resistivity, Hall coefficient, and thermopower of the misfit-layered compound, [Sr 2 O 2-δ ] p CoO 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 2 O 2-δ ] 0.53 CoO 2 shows metallic conduction down to 2 K 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 3 Co 4 O 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.
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