Search

Abstract The proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ. However, the κ of GeTe increases at the ferroelectric phase transition near 700 K. Using first-principles calculations with the temperature dependent effective potential method, we show that this rise in κ is the consequence of negative thermal expansion in the rhombohedral phase and increase in the phonon lifetimes in the high-symmetry phase. Strong anharmonicity near the phase transition induces non-Lorentzian shapes of the phonon power spectra. To account for these effects, we implement a method of calculating κ based on the Green-Kubo approach and find that the Boltzmann transport equation underestimates κ near the phase transition. Our findings elucidate the influence of structural phase transitions on κ and provide guidance for design of better thermoelectric materials.

A theoretical study based on the density functional theory and the temperature-dependent effective potential method is performed to analyze the changes in the phonon band structure as a function of temperature for indium antimonide. In particular, we show changes in the thermal expansion coefficient and the thermal resistivity that agree rather well with experimental measurements. From the theoretical side, we show a weak dependence with respect to the chosen thermostat used to obtain the inter-atomic force constants, which strengthens our conclusions. [ABSTRACT FROM AUTHOR]