Thermodynamics of heterogeneous equilibria in the In-In2O3 system using Knudsen effusion mass spectrometry

RATIONALE The In-In2O3 system is regarded as a potential low-temperature source of gaseous indium oxide (In2O) 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. METHODS The study of the In-In2O3 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. RESULTS It was established that In(g) and In2O(g) are the major vapor species over heterogeneous mixtures (In(l) + In2O3(s)) and the gaseous oxide In2O 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-In2O3 system phase diagram at 1060 K was constructed. The standard enthalpies of reactions accompanying vaporization of the In and In2O3 mixtures were evaluated using the second- and third-law methods. The standard enthalpy of formation of In2O(g) was derived from the enthalpies of reactions obtained. CONCLUSIONS The predominance of In2O in the equilibrium vapor over heterogeneous mixtures (In(l) + In2O3(s)), along with its high partial pressure at relatively low temperatures, substantiate the In-In2O3 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 In2O(g) obtained in an independent way in the present work is in good agreement with that from our previous In2O3(s) vaporization study.