ICT2014 Abstracts

Optimizing the performance of thermoelectric (TE) materials demands high value of Seebeck coefficient at the same time with high electrical conductivity and low thermal conductivity. The challenge in processing better TE materials lies in achieving this unique combination of properties for the same material. In this study we focus on the PbTe compound, which is an important TE material for the mid-temperature range.

We calculate vibrational and electronic properties for PbTe-based compounds from first-principles, applying the density functional theory (DFT), to estimate the resulted TE performance. Being one of the major terms determining lattice thermal conductivity, we calculate the average sound velocity for the pure and doped-PbTe compounds, based on the total energies of the crystals and atomic displacements. The electronic transport calculations are based on the Boltzmann transport theory. We determine both these vibrational and electronic properties applying quantitative data on phonon and charge carrier lifetimes that are documented for the PbTe-matrix.

Electronic band structure calculations enable us predict whether the resulting doped-PbTe compounds are of the p- or n-type nature, which is of great importance for TE devices. Furthermore, we can distinguish between the contributions of individual atomic orbital to the density of states and understand the influence of each dopant and impurity site. We show how Pb-p orbitals mostly contribute to the conduction band; therefore, replacing a Pb atom with an impurity atom is expected to affect the conduction band. We find that dopants of groups 4-5 in the periodic table, such as Ti, Zr, Hf, Nb, and Ta, are the most effective in reducing the lattice thermal conductivity, whereas dopants of  group 3 (Sc, Y) as well as several rare-earth elements (Gd, Tb, Dy, Ho, Er, Tm) are the most effective ones in increasing the power factor.