Chemical stability of CuInS2 in oxygen at 298 K

A thermochemical analysis is performed in the quaternary system Cu-In-S-O at 298 K, including the respective four ternaries. The Cu-In phase diagram is updated with respect to the new experimental as well as to the new thermochemical results in the literature. Free energies of In6S7, In2.8S4, CuIn2, and Cu2In2O5 have been estimated. Consistent sets of data are used for the calculations of the ternary systems with the program THERMO, and the results are used to calculate the quaternary tetrahedron Cu-In-S-O with the program THERMOQ; the algorithm is given. Twelve quaternary two-phase equilibria have been found. They are used to calculate predominance area diagrams of the quaternary system with the program STADIAQ for different oxygen partial pressures. The algorithm of this program is given. From these diagrams it becomes obvious that CuInS2 is unstable in air and even in UHV systems and should react to form In-2(SO4)(3) and Cu2S at oxygen pressures larger than log p(pascal) = -51.5. The results are useful for research in fields such as oxidation and crystal growth of CuInS2 and for development of processes for producing this compound.