Electronic structure and transport properties of Cu-deficient kuramite Cu_3-xSnS₄

Electrical and thermal transport properties of Cu-deficient kuramite Cu_3-xSnS₄ (CTS) was examined as a possible earth-abundant thermoelectric material. Crystallographic structure of CTS was characterized by partial disorder between Cu and Sn. In contrast to semiconducting electrical transport of related compounds, such as Cu₂ZnSnS₄ and Cu₃SbS₄, metallic conduction with an electrical resistivity of 0.4mΩcm and a carrier concentration of 3 x 10²¹ cm^-3 was observed at 300 K. Lattice thermal conductivity was calculated at ∼2.6Wm^-1 K^-1, which was probably reduced by Cu-deficiency and/or partial cation disorder. Density functional theory calculation indicates valence band was composed of hybridization between Cu 3d orbitals and S 3p orbitals.