Metallicity And Thermopower Of The Misfit Cobaltite [Bi2ba1.8co0.2o4](Rs)[Coo2](2)

The misfit cobaltite, [Bi2Ba1.8Co0.2O4](RS)[CoO2](2), built up from the stacking of rocksalt-type layers (RS) and single hexagonal [CoO2] layers (H), has been synthesized. This complex structure, described in a commensurate monoclinic supercell, exhibits a double commensurate modulation: a misfit modulation with b(RS)/b(H)=2 and an intrinsic modulation of the RS layers [q(i)=0.2(a(RS)+b(RS))]. This oxide is characterized by an enhanced metallic behavior with respect to the misfit Bi(Pb)/Sr/Co/O cobaltites and in contrast to these compounds by a positive magnetoresistance and significantly smaller values of the thermoelectric power (<100 μV K-1). A comparison of its behavior with those of Sr2RuO4 and of the heavy-fermion-like oxide LiV2O4 is presented.