Phonon and thermal transport properties of the misfit-layered oxide thermoelectric Ca3Co4O9 from first principles

The full phonon spectra of two rational approximants to the incommensurate thermoelectric oxide material Ca3Co4O9 (CCO) are calculated from first principles within density functional theory (DFT) and its DFT + U extension. The computed phonon dispersion curves are then used to evaluate the constant volume heat capacity, as well as the full and partial (subsystem-projected) lattice thermal conductivity of CCO. The results are discussed in terms of the effects of the Hubbard U on the computed properties, the size of the rational approximants used to model CCO, the relative contributions of the two subsystems that comprise the misfit-layered material, and the anisotropic nature of the computed thermal conductivity. We obtain good agreement with available experimental data.