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

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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 %.