Extension of the misfit series to the mercury-based cobaltites

The exploration of the Hg–Sr/Ca–Co–O system using EDS and electron microscopy has shown the possibility to incorporate mercury and excess cobalt in the middle rock salt layer of the misfit cobaltite structure, leading to the new series Hg_1−xCo_xSr_2−yCa_yO₃]^RSCoO₂]_b1/b2 with 0.6x0.90, 0y2, and b₁/b₂ ranging from 1.63 to 1.79. These new composite oxides, built up from CoO₂]_∞ layers of the CdI₂-type stacked with triple Hg_1−xCo_xSr_2−yCa_yO₃]. rock salt layers are remarkable by their large thermopower S values similarly to the thallium and lead misfit cobaltites. More importantly, the S value is sensitive to the composition of the triple rock salt layer, increasing as the calcium content increases, so that an enhancement of the figure of merit of the pure calcium compound is expected.