Metallicity and thermopower of the misfit cobaltite $\left[{\mathrm{Bi}}_2{\mathrm{Ba}}_{1.8}{\mathrm{Co}}_{0.2}{\mathrm{O}}_4{]}^{\mathrm{RS}}\right[{\mathrm{CoO}}_2{]}_2$

The misfit cobaltite, $\left[{\mathrm{Bi}}_2{\mathrm{Ba}}_{1.8}{\mathrm{Co}}_{0.2}{\mathrm{O}}_4{]}^{\mathrm{RS}}\right[{\mathrm{CoO}}_2{]}_2,$ built up from the stacking of rocksalt-type layers (RS) and single hexagonal $\left[{\mathrm{CoO}}_2\right]$ layers $\mathrm{}\left(H\right),$ has been synthesized. This complex structure, described in a commensurate monoclinic supercell, exhibits a double commensurate modulation: a misfit modulation with $b_{\mathrm{RS}}{/b}_H=2\mathrm{}$ and an intrinsic modulation of the RS layers $[q_i=0.2({\mathbf{a}}_{\mathrm{RS}}+{\mathbf{b}}_{\mathrm{RS}}\left)\right].$ 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 ${\mathrm{K}}^{\mathrm{-}1}$). A comparison of its behavior with those of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and of the heavy-fermion-like oxide ${\mathrm{LiV}}_2{\mathrm{O}}_4$ is presented.