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

The ternary system Cu–Sn–S was re-investigated and the phase diagram Cu2S–SnS2 studied in detail by differential thermal analysis and X-ray diffractometry. Three phases of composition Cu4SnS4, Cu2SnS3 and Cu2Sn3+xS7+2x(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 Cu2Sn3S7 has semiconducting properties and an absorption coefficients of the order 105 cm−1.