Thermoelectric Properties In The Misfit-Layered-Cobalt Oxides [Bi(2)A(2)O(4)] [Coo2](B1/B2) (A=Ca, Sr, Ba, B(1)/B(2)=1.65, 1.82, 1.98) Single Crystals

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(1)/b(2) ([Bi(2)A(2)O(4)][CoO2](b1/b2) with A=Ca, Sr, Ba, b(1)/b(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 mu W/cmK(2) at room temperature, which is not so trivial. We will discuss the origin of the almost unique value of 2.2 +/- 0.3 mu W/cmK(2).