Quantification of thermodynamic properties for vaporisation reactions above solid Ga2O3 and In2O3 by Knudsen Effusion Mass Spectrometry

Abstract

Even though Ga2O3 and In2O3 are broadly used as semi-conductors, thermodynamic data for their vaporisation reactions exhibit a large spread. Therefore, the vaporisation behaviour of solid Ga2O3 and In2O3 was determined by means of Knudsen Effusion Mass Spectrometry (KEMS). Ga2O3 and In2O3 were studied in an iridium Knudsen cell and heated over a temperature range of 1200–1750 K in order to identify the species present in the vapour phase, and determine their partial pressures. We find that M2O (where M = Ga or In) is the most abundant gas species above the solid oxide, followed by M and MO, in accord with tabulated data. Following the calculation of partial pressures and equilibrium constants, we propose ΔfHo 298, 3rd(Ga2O(g)) = − 68966 ± 7442 Jmol-1 and Δf Ho 298, 3rd(In2O(g)) = − 22245 ± 964 Jmol-1 from the 3rd law method. Deviations in Δf Ho 298, 3rd(i) relative to literature KEMS measurements are generally within ~2% relative, and can be ascribed to the use of different ionisation cross sections, Knudsen cell material, temperature calibrations, as well as tabulated Gibbs energy functions. However, comparison with ab initio studies suggests the data reported in this work is more accurate than in previous studies, given that the ΔfHo 298, 3rd(InO(g)) = 157744 ± 3681 Jmol-1 deviates by only ~0.2% from the theoretical value.