Comparative studies of the electronic structure and thermoelectric properties in orthorhombic and tetragonal BaCu2Se2 by first-principles calculations

Abstract

The electronic structures of BaCu₂Se₂ in two phases, orthorhombic α-BaCu₂Se₂ and tetragonal β-BaCu₂Se₂, are investigated by using first-principles calculations. For the two phases, it is found that the bottom of the conduction band primarily comes from Ba 5d orbitals while the upper valence band consists of Cu 3d and Se 4p orbitals, and both of them exhibit direct band gaps. The calculated electronic structures reveal that α-BaCu₂Se₂ has a higher Seebeck coefficient while β-BaCu₂Se₂ possesses a larger electrical conductivity. The thermoelectric properties of p-type α- and β-BaCu₂Se₂ are calculated on the base of the semi-classical Boltzmann transport theory. It is observed that the thermoelectric performance of tetragonal β-BaCu₂Se₂ is superior to orthorhombic α-BaCu₂Se₂. The optimal doping concentrations have been estimated based on the predicted maximum power factors, and the temperature dependence of Seebeck coefficient of β-BaCu₂Se₂ is also estimated and compared with experimental data, with good agreements observed.