Thermodynamics of heterogeneous equilibria in the In-In₂ O₃ system using Knudsen effusion mass spectrometry

The In-In₂ O₃ system is regarded as a potential low-temperature source of gaseous indium oxide (In₂ O) when obtaining functional materials by physical vapor deposition techniques. To date the vaporization thermodynamics of the system have been investigated in few studies, the results of which are contradictory.

The study of the In-In₂ O₃ system was performed using Knudsen effusion mass spectrometry in the temperature range 930-1210 K, with a magnet mass spectrometer (MS-1301). Quartz effusion cells heated by a resistance furnace were employed.

It was established that In(g) and In₂ O(g) are the major vapor species over heterogeneous mixtures (In(l) + In₂ O₃ (s)) and the gaseous oxide In₂ O is predominant. The partial pressures of the vapor species were determined and the quantitative vapor composition was calculated. Based on the experimental data, a p-x section of the In-In₂ O₃ system phase diagram at 1060 K was constructed. The standard enthalpies of reactions accompanying vaporization of the In and In₂ O₃ mixtures were evaluated using the second- and third-law methods. The standard enthalpy of formation of In₂ O(g) was derived from the enthalpies of reactions obtained.

The predominance of In₂ O in the equilibrium vapor over heterogeneous mixtures (In(l) + In₂ O₃ (s)), along with its high partial pressure at relatively low temperatures, substantiate the In-In₂ O₃ system to be suitable for physical vapor deposition methods. The obtained results can be used for physical vapor deposition parameter adjustment and optimization. The standard enthalpy of formation of In₂ O(g) obtained in an independent way in the present work is in good agreement with that from our previous In₂ O₃ (s) vaporization study.