Structural evolution of NiAg heterogeneous alloys upon annealing

NiAg heterogeneous alloys were studied by x-ray diffraction and x-ray absor ption spectroscopy at the Ni K-edge using a total electron yield detection. In the as-deposited NixAg1-x alloys of 0.10 and 0.15 Ni atomic fraction, m ost of the Ni atoms are in substitutional sites in the Ag matrix. At higher Ni concentration, the Ni atoms outside the Ag-rich phase become numerous e nough to group together in small clusters. An important disorder in the nei ghbourhood of Ni atoms is demonstrated. At low annealing temperature (up to 250 degrees C), in Ni0.20Ag0.80 and Ni0.35Ag0.65, some Ni atoms are still present in substitutional sites in the Ag matrix and the small Ni particles are under strain. A very shea-range order exists in this state. After a 25 0 degrees C annealing, the Ni particles grow, and the Ag-rich phase remains in a steady structural state. After a higher annealing (400 degrees C), th e local Ni atomic environment becomes well ordered and typical of the pure Ni FCC phase. The Ag-rich crystallites are impoverished in Ni atoms and gro w with elimination of defects. Ni grains are generally smaller than 1 nm fo r as-deposited alloys and reach several nanometres after a 400 degrees C an nealing for 10 min.