Local atomic structural changes on structural relaxation in a Pd 82Si 18 amorphous alloy

Abstract

The microstructural changes on low temperature annealing of amorphous Pd 82Si 18 ribbon specimens were observed using high-resolution electron microscopy and the results were correlated with the structural relaxation. At the initial stage of annealing up to 573 K, atomic medium-range order (MRO) develops and grows. At temperatures higher than 573 K but below the glass transition temperature, the MRO domains grow to f.c.c. nanocrystals which change the profile of the electron diffraction pattern, especially of the second halo ring. According to nano-beam elemental analysis on annealing using sputter-deposited Pd 82Si 18 thin films, the Si content in the MRO domains and nano-precipitates decreases as the domain or particle size increases. It is concluded that the atomic free volume introduced during amorphization is annihilated by atomic rearrangement in the formation and development of the MRO domains, and the chemical order must be developed in the dense random packing (DRP) matrix by the diffusion of Si from MRO into the matrix. The structural relaxation corresponds to these local atomic structural changes.