The Structure of a Metastable Au–Sn Phase Determined by Convergent Beam Electron Diffraction

Abstract

The structure of a new metastable Au–Sn phase was determined by convergent beam electron diffraction. Micrometer-sized crystals were grown by heating a metal/oxide/metal trilayer and allowing the metals to react. The new phase was tetragonal with space groupP4/nbm, lattice parametersa= 6.63(3) Å andc= 5.92(3) Å, and composition AuSn4. The phase was found to be isostructural with PtPb4with Au atoms located at 2(a) sites and Sn atoms at 8(m) sites. Conditional Patterson transforms parallel to thec-axis were calculated from the quasi-kinematic intensities of first-order Laue zone (FOLZ) reflections diffracted from Bloch states localized on the Sn atom strings. The contour maps showed clear peaks from Au–Sn and Sn–Sn interatomic vectors. A least-squares refinement using the FOLZ reflections gave the Sn atomic parameters asx= 0.167(1),z= 0.25(4).