The vaporization processes for Ga2S3, Ga2Se3 and Ga2Te3 have been studied at elevated temperatures by the Knudsen effusion and mass spectrometric techniques. The solids vapourize primarily by the reaction Ga2X3(s) = Ga2X(g)+X2(g), where X = S , Se and Te. The heats of reaction at 298°K for the sulphide, selenide and telluride were 161 If6, 168i-7 and 162*7 kcal mole-', respectively. The gaseous molecules GaTe, Ga,Te2 and GaTe2 were also found in the vapour phase above the solid Ga2Tes and the following gaseous equilibria were studied :The atomization energies for the gaseous gallium chalcogenides were estimated to be Dg(Ga2S) = Dg(Ga2Te) = 11937 kcal mole-', 189f7 kcal mole-', Dg(GaTe) = 59f6 kcal mole-', and Dg(GaTe2) = 21 1 *6 kcal mole-'. D;(Ga2Se) = 1 4 9 i 8 kcal mole-', Mass spectrometric techniques have been employed extensively for the study of the vaporization processes of the group 3~ oxides, M 2 0 3 , and the measurement of the thermodynamic stabilities of the gaseous species in the vap0urs.l Similar studies have been conducted for B,S,(s) and In2S3(s).3 Recently, gaseous equilibrium studies have been used to establish the stabilities of AlS, AlSe and A1Te,4 and of the molecules InX, h 2 X , In,X, (X = S, Se, Te), and InTe,.'.This work reports studies of the vaporization processes for the solids Ga,S,, Ga,Se, and Ga,Te,, including the identification of the equilibrium vapour species, and determinations of the thermodynamic stabilities of these gaseous molecules.
EXPERIMENTALA Bendix time-of-flight mass spectrometer, model 14-206A7 equipped with a watercooled Knudsen cell assembly similar to that described previously,6 was used. The spectrometer is equipped with five analogue read-outs for simultaneously monitoring the intensities of different ion species during the temperature-dependence measurements.Samples of Ga2S3, Ga2Se3 and GazTe3 were heated individually in tantalum crucibles fitted with alumina liners which have knife-edged orifices of 0.5 mm. diam. The Knudsen cells were heated by radiation and electron bombardment from two 10-mil tungsten filaments.Temperatures were measured with a Pt/Pt-10 % Rh thermocouple pressed into a hole in the bottom of the cell.Appearance potential measurements were made by the linear extrapolation method and by the use of an X-Y recorder, while temperature-dependence intensity data were measured with a two-pen strip-chart recorder. For the GazTe3 system where more than two peaks were monitored simultaneously, pairs of intensities were alternatively recorded by switching
