Thermoelectric properties in the misfit-layered-cobalt oxides Bi{sub}2A{sub}2O{sub}4CoO{sub}2{sub}(b{sub}1/b{sub}2) (A=Ca, Sr, Ba, b{sub}1/b{sub}2=1.65, 1.82, 1.98) single crystals

摘要

Single crystals of different phases of misfit cobalt oxides have been synthesized. Using these materials, the intrinsic power factor has been determined. By combining thermopower S and Hall coefficient measurements, we will show how S can be tuned by doping in this family of materials, the doping being strongly dependent on the misfit ratio p=b{sub}1/b{sub}2 ([Bi{sub}2A{sub}2O{sub}4][CoO{sub}2]{sub}(b{sub}1/b{sub}2) with A=Ca, Sr, Ba, b{sub}1/b{sub}2=1.65, 1.82, 1.98). The in-plane resistivity also strongly depends on the doping: the more metallic samples are obtained for the largest carrier concentration, i.e. the smaller S value. The combination of these two factors leads to an important conclusion that the power factor is independent of the doping in these Bi-based materials converging to a unique value of 2.2±0.3 μW/cm K{sup}2 at room temperature, which is not so trivial. We will discuss the origin of the almost unique value of 2.2±0.3 μW/cm K{sup}2.