Structural, electronic, and thermoelectric properties of La2CuBiS5

Abstract

The basic physical properties of La2CuBiS5are studied by the first-principle calculations and the semiclassical Boltzmann theory. Charge density difference calculations show that electrons accumulate between Bi–S atoms, indicating considerable covalent bonding of Bi and S atoms. A similar charge density difference indicates that the Cu–S bonds also exhibit covalent character. The calculated minimum thermal conductivity of La2CuBiS5is low, which is conducive to its use as a thermoelectric material. Owing to a bipolar effect, induced by thermal excitation, the material’s Seebeck coefficient decreases sharply at T = 800 K. For the n-type and p-type doping conditions, the largest values of S2σ/τ were calculated as −1.71×1011and 1.837×1011W K−2ms−1, respectively. The combination of a large dispersion and a high band degeneracy along the Γ-Y direction in the band structure simultaneously induces the highest Syvalue and a high σ/τyvalue. Thus, the thermoelectric performance of La2CuBiS5is anisotropic and most favorable along the y direction.