Conductivity Phase Transition with Shift of Valence-Band Edge and with Structural Distortion in Cu4Sn1-xGexS4

Abstract

X-ray diffraction, electrical resistivity, DSC and XPS investigations were carried out on Cu 4 Sn 1- x Ge x S 4 (0≤ x ≤1.0). At room temperature, the orthorhombic structure changes to a monoclinic one at a transition concentration of x t =0.6 as x increases. This transition also exhibits the expansions in the energy width between the top of the valence band and the Fermi level and in the lattice parameter B . The transition has the characteristics of the first-order high (high temperature)-to-low (low temperature) conductivity phase transition as reported on Cu 4 SnS 4 . The transition temperature T t linearly increases with x . These features are briefly compared with the electronic and structural phase transition reported on SnTe and Pb 1- x Ge x Te.