Thermodynamic modeling of the Pd–Zr system

The thermodynamic properties and phase diagram of the Pd–Zr system have been analyzed by the CALPHAD technique using a computational optimization procedure. Based on the experimental data, the solution phases (liquid, body-centered cubic (Zr), face-centered cubic (Pd) and hexagonal close-packed (Zr)) were modeled with the Redlich–Kister equation. Both compounds Pd2Zr and PdZr2 having a tetragonal MoSi2-type structure were treated as one phase with the formula PdZr(Pd, Zr) by a three-sublattice model with Pd on the first sublattice, Zr on the second and Pd and Zr on the third one, respectively. A three-sublattice model (Pd,Zr)0.5(Pd,Zr)0.5(V a)3 is applied to describe the compound γ PdZr in order to cope with the order–disorder transition between body-centered cubic solution (A2) and γ PdZr with CsCl-type structure (B2). Another three-sublattice model (Pd,Zr)0.75(Pd,Zr)0.25(V a)0.5 is applied to describe the compound Pd3Zr in order to cope with the order–disorder transition between hexagonal close-packed (A3) and Pd3Zr with Ni3Ti-type structure (D024). The other compounds were treated as stoichiometric compounds. A set of self-consistent thermodynamic parameters of the Pd–Zr system was obtained.