Diffusion in metallic glasses and deeply undercooled liquids was analyzed using the concept of so-called atomic bond deficiency. The process was considered to be thermally activated hopping of diffusing atoms between the first nearest-neighbour and the second-nearest neighbor positions at the bond deficiency defects. Cooperative movements of multiple adjacent atoms were required because of (1) the small extra volumes created by bond deficiency defects and (2) the short-range-only constraint. The activation energy Q depended upon the bond strengths, size of diffusing atoms, the elasticity of the matrix and the effective number of the involved matrix atoms. Application to tracer diffusion in Zr–Ni and Ti–Ni shows that 10 or fewer matrix atoms might be involved, and the size effect of diffusing atoms on Q agreed with experimental measurements. Other observations, including

the sharp slope of the Q versus pre-exponential factor, the isotope and pressure effects were explained.

Diffusion in Metallic Glasses - Analysis from the Atomic Bond Defect Perspective. A.Zhu, G.J.Shiflet, S.J.Poon: Acta Materialia, 2008, 56[14], 3550-7