Structure determination of a new metastable Au-Sn phase using convergent beam electron diffraction

Abstract

Reports of a new metastable Au-Sn phase led to the investigation of this system by Convergent Beam Electron Diffraction (CBED). A novel growth route was used, in which a single metallic layer of Sn was evaporated onto rock salt and allowed to form a thin oxide layer, before a film of gold was evaporated directly on top. Subsequent in-situ heating in a TEM supplied enough energy to allow solid state diffusion of Sn through the oxide to react with the Au, forming a number of intermetallic phases.A new tetragonal AuSru phase was found, space group P4/nbm and lattice parameters a=6.63Å, c=5.92Å, and it was proposed that this new phase was isostructural with PtPb4 . Further work described here confinns this structure type and shows how the atomic positions were refined using First Order Laue Zone (FOLZ) reflections within a quasi-kinematic approximation.Fig. 1 shows a section of the FOLZ at the [001] zone axis of this new Au-Sn phase.