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Electronic structures of orthorhombic and monoclinic Cu4SnS4, which exhibit a first-order phase transition at 232 K, are demonstrated based on the generalized gradient approximation (GGA) of the density functional theory (DFT). The calculated band gap was 0.39 eV for orthorhombic phase, while that was not obtained for monoclinic one. These calculated results confirm monoclinic phase has smaller activation energy ( Ea) than orthorhombic phase. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Electronic structures of orthorhombic and monoclinic Cu4SnS4, which exhibit a first-order phase transition at 232 K, are demonstrated based on the generalized gradient approximation (GGA) of the density functional theory (DFT). The calculated band gap was 0.39 eV for orthorhombic phase, while that was not obtained for monoclinic one. These calculated results confirm monoclinic phase has smaller activation energy ( Ea) than orthorhombic phase. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The thermoelectric properties and electronic band structures for Se-doped Co 3 SnInS 2 were examined. The parent compound of this material (Co 3 Sn 2 S 2 ) has two kinds of Sn sites (Sn1 and Sn2 sites). The density functional theory (DFT) calculations show that the indium substitution at the Sn2 site induces a metallic band structure, on the other hand, a semiconducting band structure is obtained from substitution at the Sn1 site. However, according to the previous reports, since the indium atom prefers to replace the tin atom at the Sn1 site rather than the Sn2 site, the resistivity of Co 3 SnInS 2 shows semiconducting-like behavior. In this study we have demonstrated that metallic behavior and a decrease in resistivity for Se-doped Co 3 SnInS 2 occurs without suppression of the Seebeck coefficient. From the DFT calculations, when the selenium content is above 0.5, the total crystallographic energy shows that a higher indium occupancy at Sn2 site is more stable. Therefore, it is suggested that the selenium doping suppress the site preference for indium substitution. This is one of the possible explanations for the metallic conductivity observed in Se-doped Co 3 SnInS 2 [ABSTRACT FROM AUTHOR]