Sublattice occupancies of Pd in Cu0.5Au0.5−xPdx alloys by ALCHEMI

Abstract

The composition dependence of the lattice parameters of Cu0.5Au0.5−xPdx (0<x<0.25) alloys with the face-centered tetragonal ordered L10 structure has been measured by X-ray diffraction. The results confirm the behavior reported earlier by Nakahigashi et al. Whereas the unit cell volume decreases monotonically with increasing palladium content, the axial ratio c/a exhibits a maximum at about 4 at. % Pd, corresponding to local minimum and maximum values for a and c, respectively. In theoretical modelling of this behavior it was assumed that Pd atoms were randomly interchangeable with only Au atoms. Several techniques, including the ALCHEMI method, are being used to measure directly the sublattice occupancy of palladium.Electropolishing with various solutions failed to produce good quality specimens for analytical electron microscopy (AEM). Ion milling of specimens previously electropolished with an electrolyte of 10% perchloric acid in acetic acid was more successful. Analyses were performed with Philips EM400T/FEG and CM12/STEM instruments and EDAX 9100/70 and 9900 energy dispersive X-ray microanalysis systems.