Electronic structure of the $\mathrm{C}{\mathrm{a}}_3\mathrm{C}{\mathrm{o}}_4{\mathrm{O}}_9$ compound from ab initio local interactions

Abstract

We used fully correlated ab initio calculations to determine the effective parameters of Hubbard and t - J models for the thermoelectric misfit compound $\mathrm{C}{\mathrm{a}}_3\mathrm{C}{\mathrm{o}}_4{\mathrm{O}}_9$. As for the $\mathrm{N}{\mathrm{a}}_{\mathrm{x}}\mathrm{Co}{\mathrm{O}}_2$ family the Fermi level orbitals are the $a_{1g}$ orbitals of the cobalt atoms ; the $e_g^{\prime }$ being always lower in energy by more than 240\,meV. The electron correlation is found very large $U/t\sim 26$ as well as the parameters fluctuations as a function of the structural modulation. The main consequences are a partial $a_{1g}$ electrons localization and a fluctuation of the in-plane magnetic exchange from AFM to FM. The behavior of the Seebeck coefficient as a function of temperature is discussed in view of the ab initio results, as well as the 496\,K phase transition.

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Cited by in corpus (3)

• Crossover from itinerant to localized states in the thermoelectric oxide [Ca${}_2$CoO${}_3$]${}_{0.62}$[CoO${}_2$]
• Thermoelectric properties of the misfit cobaltate Ca${}_3$Co${}_4$O${}_9$
• Origin of the high Seebeck coefficient of the misfit [Ca${}_2$CoO${}_3$]${}_{0.62}$[CoO${}_2$] cobaltate from site-specific valency and spin-state determinations