Mass spectrometric studies of the Decomposition and the Heat of Formation of CuInS₂(s)

The equilibrium vaporization of CuInS 2 (s) was studied by Knudsen cell mass spectrometric techniques in the temperature range 902—1110 K. Based on these and independent congruency studies, CuInS 2 (s) decomposes under steady‐state conditions according to the reaction 2CuInS 2 (s) = Cu 2 S(s) + In 2 S(g) + S 2 (g). During the initial transient period of the vaporization of CuInS 2 , the ion intensities of In 2 S + and S 2 + change and assume steady‐state values after some time. A second‐law evaluation of intensity versus temperature data, obtained under steady‐state conditions, yielded a value for the heat of the above decomposition reaction (2 moles of CuInS 2 ) of δH 630.9 ± 26 kJ. With this quantity and auxiliary thermochemical data, the enthalpy of formation of CuInS 2 (s) was computed to be δH = −221.7 ± 13 kJ/mol.