Lattice contribution to the high dielectric constant of PbTe

Abstract

The phonon dispersion and the lattice contribution to the dielectric function of PbTe in the NaCl structure are calculated ab initio. The results obtained are in agreement with the available experimental data and reproduce the main features observed in this material, such as an anharmonic LA-TO phonon coupling in the $\ensuremath{\Gamma}$-X direction, as well as high values for the dielectric constants ${\ensuremath{\epsilon}}_{1}(0)$ and ${\ensuremath{\epsilon}}_{1}(\ensuremath{\infty})$. Calculations include the pressure dependence and indicate that the anharmonic phonon coupling is very sensitive to applied pressure. The calculations indicate that the higher values for the dielectric constant together with the anharmonic LA-TO coupling reduce the lattice thermal conductivity and increase the internal electric field, thereby enhancing the electronic conductivity in PbTe, key conditions to increase the thermoelectric figure of merit.