Phase relations and optical properties of semiconducting ternary sulfides in the system Cu–Sn–S

The ternary system Cu–Sn–S was re-investigated and the phase diagram Cu 2S–SnS 2 studied in detail by differential thermal analysis and X-ray diffractometry. Three phases of composition Cu 4SnS 4, Cu 2SnS 3 and Cu 2Sn 3+ x S 7+2 x (0≤×≤1) were found exhibiting melting points at 833, 856 and 803 °C, respectively. Ellipsometric and diffuse reflectance measurements revealed that the latter two sulfides possess a fundamental band gap of 0.93 eV followed by a higher transitions. For the first time it could be demonstrated that Cu 2Sn 3S 7 has semiconducting properties and an absorption coefficients of the order 10 5 cm −1.