Nano-block integration in the misfit layered Co oxides

The layered cobalt oxides having the CdI2-type hexagonal CoO2 layer exhibit good thermoelectric properties especially at high temperatures. Above all, the misfit layered Co oxides [A2MnO2+n-d]yCoO2 are of particular interest, in which the CoO2 layer and the NaCl-type tetragonal block-layer stack alternately along the crystallographic c axis. We prepared single crystals for various kinds of misfit layered Co oxide, and measured the thermoelectric properties to investigate how the block layer affects the electronic states of the CoO2 layer. We found that the room-temperature thermopower monotonically increases with the misfit ratio y, which we associated with short-ranged spin-density-wave modulated by the interfacial stress between the layers.