In-situ investigation of the kesterite formation from binary and ternary sulphides

The formation of kesterite (Cu₂ZnSnS₄) from different stoichiometric mixtures of binary and ternary sulphides was investigated by in-situ high temperature synchrotron X-ray diffraction. The data were collected during the heating, the annealing and the cooling cycle. The Rietveld analysis of the diffractograms led us to determine temperature dependent phase changes qualitatively and quantitatively as well as the lattice constants of the different phases. Showing exemplarily with the mixture 2CuS + SnS + ZnS the formation of Cu₂ZnSnS₄ starts just below 300 °C. The volume size of the fcc anion substructure of the newly formed kesterite at 300 °C corresponds to the one of the ZnS phase. The lattice parameter of Cu₂ZnSnS₄ increases nonlinearly with increasing temperature showing possibly the trend of different formation stages. Comparing the lattice constants a and c of the several synthesized kesterites at 700 °C among each other and with a pre-synthesized kesterite, remarkable variations were obtained, whereas the ratio of the lattice parameter (c/2a) is comparable. These features led to the assumption that the cation distribution may vary in dependence on temperature and on the phase mixture used as starting material.