Thermodynamic properties of PbTe, PbSe, and PbS: First-principles study

The recent discoveries of novel nanocomposite and doped lead chalcogenide-based thermoelectric materials have attracted great interest. These materials exhibit low thermal conductivity which is closely related to their lattice dynamics and thermodynamic properties. In this paper, we report a systematic study of electronic structures and lattice dynamics of the lead chalcogenides PbX (X=Te, Se, and S) using first-principles density-functional- theory calculations and a direct force-constant method. We calculate the structural parameters, elastic moduli, electronic band structures, dielectric constants, and Born effective charges. Moreover, we determine phonon dispersions, phonon density of states, and phonon softening modes in these materials. Based on the results of these calculations, we further employ quasiharmonic approximation to calculate the heat capacity, internal energy, and vibrational entropy. The obtained results are in good agreement with experimental data. Lattice thermal conductivities are evaluated in terms of the Grüneisen parameters. The mode Grüneisen parameters are calculated to explain the anharmonicity in these materials. The effect of the spin-orbit interaction is found to be negligible in determining the thermodynamic properties of PbTe, PbSe, and PbS.