The layered cobalt oxides show large thermopower, low resistivity, and low thermal conductivity, and are a promising material for thermoelectric power generation. They share the CdI2-type hexagonal CoO2 layer as a common unit, where large entropy of kBlog6 is stored on Co4+ ion. They show large anisotropy between the in-and out-of-plane directions depending on the block layers. Lattice thermal conductivity is smaller for heavier ions. Some of them show a characteristic misfit structure, which induces a significant in-plane anisotropy.
