Experimental redetermination of the Cu–Pd phase diagram

The equilibrium Cu–Pd phase diagram has been experimentally reinvestigated in the 300–680 °C temperature region by powder XRD involving a high-temperature technique. To reduce the annealing time needed for the system to attain the equilibrium state, nanosized specimens with a characteristic crystallite size of 5–15 nm were used initially. All previously reported phases, i.e., a disordered face-centered cubic solid solution Cu_1-xPd_x (A1), a one-dimensional long-period superlattice structure Cu₂₁Pd₇ (1D–LPS), intermetallic compounds Cu₃Pd (L1₂) and CuPd (B2), except a two-dimensional long-period superlattice structure (2D–LPS), could be confirmed. Homogeneity ranges of all solid phases existing in the Cu–Pd system were determined at distinct temperatures. The largest deviation of the solubility limits was observed for the Pd-rich boundary of the Cu₃Pd region (25–30 at.% Pd) and the Cu-rich boundary of the Cu_1-xPd_x region in the compositional range >55 at.% Pd. Based on the present experimental results, the constitutional Cu–Pd diagram was modified.