Thermodynamic description of the Ce–Ga and Ga–Gd systems

Abstract

The Ce–Ga and Ga–Gd systems are critically assessed by means of the calculation of phase diagram (CALPHAD) technique. The excess Gibbs energy of the solution phases [liquid, orthorhombic (Ga), fcc (Ce), bcc (Ce or Gd), and hcp (Gd)] is modeled with the Redlich–Kister equation. In the Ce–Ga and Ga–Gd systems, the intermetallic compounds, CeGa, Ce3Ga2, Ce3Ga, α-CeGa6, β-CeGa6, GaGd, Ga6Gd, Ga2Gd3, and Ga3Gd5 are treated as stoichiometric compounds. The intermetallic compounds CeGa2 and Ga2Gd with a homogeneity range, are treated using a two-sublattice model as the formula (Ce,Ga)0.333333(Ce,Ga)0.666667, and (Ga,Gd)0.666667(Ga,Gd)0.333333, respectively. In the Ce–Ga system, there are nine invariant reactions, and five stoichiometric intermetallic compounds and the compound CeGa2 with a homogeneity domain ranging from about 66.67 to 77.94 at.% Ga. Some improvements are obtained based on the experimental data in the present work, the liquidus line is more close to the most experimental points, and the homogeneity range of the compound CeGa2 seems more reasonable at full temperature range. In the Ga–Gd system, there are eight invariant reactions, and four stoichiometric intermetallic compounds and the compound Ga2Gd with a homogeneity domain ranging from about 19.64 to 33.33 at.% Gd. The present phase diagram and thermodynamic properties of the system are well reproduced with the experimental data.