Thermodynamics and surface properties of liquid Ga-In alloys

The Ga-In phase diagram is of the simple eutectic type, with the eutectic point occurring at 15°C. Such low-melting Ga-In alloys are of the great importance in the production of contact alloys, and nowadays are the base for ternary alloys of Ga-In-Me (Me=Ge, Sb, Bi) type, applied in the production of different semiconducting elements and devices. The results of thermodynamic and surface properties investigations of liquid Ga-In alloys are presented in this paper. Thermodynamic investigation was done by Oelsen calorimetric measurements. Based on the obtained enthalpy isotherm diagram, the values for the activities, activity coefficients, partial and integral molar quantities were determined in the temperature interval 400-600K. The mixing behaviour of Ga-In system has been investigated by the Quasi-Chemical Approximation (QCA) in the frame of the Quasi-Lattice Theory (QLT) combined with a statistical mechanical theory. Assuming the order energy parameters as temperature dependent, various thermodynamic quantities are calculated at different temperatures. Thermodynamic properties of Ga-In system deviate positively from the Raoult's law. The energetic of mixing in liquid alloys has been analysed through the study of surface properties (surface tension and surface composition) and microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter). Theoretical results are in a good agreement with the corresponding literature data and support a demixing tendency in Ga-In liquid alloys.