Phase equilibria in the system AueCueSi and structural characterization of the new compound Au5 xCu2 xSi

The ternary AueCueSi system was investigated by means of powder X-ray diffraction (XRD) for phase identification, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) for microstructures and chemical compositions, light optical microscopy (LOM), and differential thermal analysis (DTA) for the determination of thermal effects. Three isothermal sections were constructed at 250 C, 400 C and 650 C. A new ternary compound s, Au5 xCu2 xSi, was identified and its crystal structure was determined by means of single crystal X-ray diffraction. It adopts a new crystal structure type in space group Pnma, Pearson symbol oP32 and shows a composition range between Au5.6Cu1.4Si and Au4.4Cu2.6Si at 250 C. Lattice parameters were found to vary between a 1⁄4 9.64e9.50 A, b 1⁄4 7.61 e7.64 A and c 1⁄4 6.90e6.89 A from the Au-rich to the Au-poor composition limit. Three vertical sections, at 10 and 30 at.% Si and at 10 at.% Cu, were constructed based on DTA data and four invariant ternary phase reactions were identified. A partial ternary reaction scheme (Scheil diagram) and a partial liquidus projection are given. 2013 Elsevier Ltd. All rights reserved.