First principles study of the structural, electronic and thermoelectric properties of misfit cobaltite

In the context of environmental issues that become more and more prevalent in our society, there has been recently an increase of interest for thermoelectric (TE) materials, which have the property to convert heat into electricity, and vice-versa. Although they do not display exceptional thermopower (in comparison to best thermoelectric like bismuth telluride), oxide materials have attracted some attention for high-temperature TE applications, due to their high stability. Amongst them, CoO2-layered compounds were proposed as good p-type TE candidates. Still, these compounds have been only poorly characterized both theoretically and experimentally. In this work we report a first-principles study of misfit calcium cobaltite (Ca2CoO3)(CoO2)1.618 based on density functional theory and an hybrid functional. The computed structural, electronic and magnetic properties match well the avalaible experimental data. Then the thermoelectric properties can be deduced using the Boltzmann transport formalism within the constant relaxation time approximation and will be discussed.