Excess Thermodynamic Properties of Solutions in Ln-Ru (Ln = Nd, Gd, Dy) Binary Systems Based on Quadratic, Exponential and Combined Models Supported by Ab-Initio Calculations

The systematic thermodynamic optimization of the Ln-Ru (where Ln = Nd, Gd, and Dy) binary systems is performed using the CALPHAD approach. Using this approach, experimental information published in literature, including both phase equilibria and thermodynamic data, are critically evaluated. The thirteen intermediate phases with stoichiometries, such as Ln(3)Ru, Nd5Ru2, Ln(7)Ru(3), Nd5Ru3, Ln(73)Ru(27), Ln(2)Ru, and LnRu(2), which have been reported for the three binary Ln-Ru systems are considered as stoichiometric compounds. An exponential and a quadratic model are used to describe the temperature dependence of the excess quantities for the Liquid, (alpha Nd), (beta Nd), (alpha Dy), (beta Dy), (alpha Gd), (beta Gd), and (Ru) solution phases. The results were compared with those from a combined quadratic-exponential temperature dependence description of the excess energies. Using the Thermo-Calc software, self-consistent sets of thermodynamic parameters were obtained to describe the Gibbs energies of the numerous phases in the Ln-Ru binary systems. The calculated results are in good agreement with the available phase equilibria and thermodynamic data.