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 [A₂M_nO_2+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