Electrical and thermal transport properties of Cu-deficient kuramite Cu3-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.
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