Evaporation thermodynamics and sublimation of aluminum telluride

Abstract

The analysis of the researches completed by now showed the lack of information concerning the definition of quantity of the vapor pressure values over the molten and crystalline aluminum chalcogenide. In the work presented here, the saturated vapor pressure over liquid and crystalline aluminum sesquitelluride was determined for the first time by the boiling point method (isothermal version). The compound was synthesized from elements, with a purity of 99.99 wt. %, identified by X-ray phase analysis as a monophase Al₂Te₃ was used as a research object. Certain vapor pressure of liquid Al₂Te₃ corresponds to the dependence, vapor pressure over crystalline telluride is  Based on the values of saturated vapor, the temperature dependence of the Gibbs free energy of evaporation and sublimation was determined, by differentiating which concerning temperature, the entropies of the condensed phase - vapor transformation were calculated, and then the enthalpy. Thermodynamic functions were as follows: entropy of evaporation of the liquid phase - 60.71 ± 4.08 J/(mol K), enthalpy - 98.65 ± 6.64 kJ/mol; entropy of sublimation of the crystalline phase - 69.37 ± 4.67 J/(mol K), enthalpy - 108.73 ± 7.31 kJ/ mol.  The low value of entropy of the aluminum telluride transfer to the vapor phase indicates the presence of associates in the vapor and of the congruent character of evaporation and sublimation of Al₂Te₃ indirectly. Defined as the difference between the sublimation enthalpies and evaporation, the enthalpy of aluminum telluride melting was 10.08 ± 0.68 kJ/mol, the entropy calculated similarly was 8.66 ± 0.58 J/(mol K). The data obtained coincide with the thermodynamic values found by other authors by calorimetric methods.