Thermodynamic assessment of phase diagram and concentration–temperature dependences of properties of solid solutions of the GaS–GaSe system

Abstract

Experimental data for the system GaS–GaSe were subjected to a critical assessment using the differential thermal analysis (DTA), X-ray diffraction and thermodynamic approach. The physicochemical and thermodynamic parameters of the GaS and GaSe compounds were taken from the literature and the authors’ previous assessment, respectively. To reach a self-consistent thermodynamic description for the constituent phases in the system, the experimental on the melting point, the composition of the minimum point and the univariant curves of the GaS–GaSe system were reassessed. An ideal solution model for the liquid, which included non-molecular compounds, was employed to represent phase diagram and Gibbs free energy of mixing data. To make our investigation on invariant points more accurate, a new and complementary experimental DTA determination regarding the compounds was carried out. We clarify the temperature and melting enthalpy of the compounds that are needed to calculate thermodynamic parameters of the system. Our thermodynamic description, compatible with experimental data for the GaS–GaSe system, resulted in an agreement between the calculated and experimental data. The temperature–concentration dependences of the properties (thermodynamic functions, the width of the forbidden band, the heat capacity) of solid solutions of the GaSe–GaS system are established. Optical value was obtained on single-crystal samples. Solid solutions of the ${\text{GaSe}}_{{ 1- {\text{x}}}} {\text{S}}_{\text{x}}$ compounds were grown by the Bridgman method by directional crystallization.