Pressure dependent thermoelectric properties of B1 and B2 phases of BaS

Abstract

In this work the first-principles calculations of the electronic and thermoelectric properties of the B1 and B2 phase of BaS have been attempted. The LCAO method has been applied considering the Perdew-Wang exchange correlation functional. The calculated lattice constant, bulk modulus and band gap have shown very good agreement with other theoretical and experimental data. The band structures have revealed that the B1 phase has indirect band gap of 2.31 eV and B2 phase has indirect band gap of 1.66 eV. By performing pressure dependent calculations, the volume deformation potentials αp and βp have been evaluated. The values of the two potentials for the B1 crystal are -4.02 meV.kbar-1 and 6.246× 10-3 meV.kbar-2, respectively. For the B2 crystal the corresponding coefficients are -1.083 meV.kbar-1 and -2.669 × 10-3 meV.kbar-2, respectively. The Seebeck coefficient, thermal conductivity, and power factor have been assessed under the rigid band and constant relaxation time approximation by combining the E-k spectra with the Boltzmann transport equations. The B1 phase has p-type carriers and the thermoelectric properties improve with increase in pressure. The power factor degrades with pressure at 300K while at 500K the performance improves. On the contrary, B2 phase has p-type carriers and its performance degrades with pressure. The current study finds that both compounds are good thermoelectric.