Phases of the NiAs family in Cu-Pd-Sn and Au-Pd-Sn systems

Phases with with a NiAs-based structure have been studied in Au-Pd-Sn and Cu-Pd-Sn systems at 500°C using powder X-ray diffraction, X-ray structure analysis, and energy-dispersive X-ray microanalysis. In the Cu-Pd-Sn system, binary phases γ-Pd₂Sn and Cu6Sn5 both having the Ni2In structure form a phase region (Pd,Cu)_{2 − x} Sn, which preserves the Ni₂In structure and is confined at 500°C by an L + (Pd,Cu)_{2 − x} Sn + ɛ-Cu₃Sn three-phase region. In the Au-Pd-Sn system, the δ-AuSn phase with the NiAs structure and γ-Pd₂Sn with the Ni₂In structure form a single phase region (Pd,Au)_{2 − x} Sn, which is bounded at 500°C by an L + (Pd,Au)_{2 − x} Sn two-phase region; the structure of the ternary phase changes from Ni2In with incompletely filled trigonal-prismatic interstices to NiAs. The Pd₂₀Sn₁₃ phase, which crystallizes in the GaGe₂Ni₄ type structure, penetrates into both ternary systems up to ∼5 at % of the third component. The solubilities of copper and gold in PdSn and Pd₂Sn phases, which have structures based on orthorhombically distorted NiAs and Ni₂In lattices, respectively, do not exceed 2 at %.