Stability of naturally relevant ternary phases in the Cu-Sn-S system in contact with an aqueous solution.

A relevant research effort is devoted to the synthesis and characterization of phases belonging to the ternary system Cu-Sn-S, mainly for their possible applications in semiconductor technology. Among all ternary phases, kuramite, Cu3SnS4, mohite, Cu2SnS3, and Cu4Sn7S16 have attracted the highest interest. Numerous studies were carried out claiming for the description of new phases in the ternary compositional field. In this study, we revise the existing literature on this ternary system, with a special focus on the phases stable in a temperature range at 25 C. The only two ternary phases observed in nature are mohite and kuramite. Their occurrence is described as very rare. A numerical modelling of the stable solid phases in contact with a water solution was underwent to define stability relationships of the relevant phases of the system. The numerical modelling of the Eh-pH diagrams was carried out through the phreeqc software with the lnll.dat thermodynamic database. Owing to the complexity of this task, the subsystems Cu-O-H, Sn-O-H, Cu-S-O-H and Sn-S-O-H were firstly considered. The first Pourbaix diagram for the two naturally relevant ternary phases is then proposed.