Tracer diffusion in amorphous solid is studied by mean of -bubble statistic. The -bubble is defined as a group of atoms around a spherical void and large bubble that represents a structural defect which could be eliminated under thermal annealing. It was found that amorphous alloys such as ( , 81.5 and 70) and suffer from a large number of vacancy bubbles which function like diffusion vehicle. The concentration of vacancy bubble weakly depends on temperature, but essentially on the relaxation degree of considered sample. The diffusion coefficient estimated for proposed mechanism via vacancy bubbles is in a reasonable agreement with experiment for actual amorphous alloys. The relaxation effect for tracer diffusion in amorphous alloys is interpreted by the elimination of vacancy bubbles under thermal annealing. 1. Introduction Metallic phases with amorphous structure are currently a subject of intensive studies not only due to their wide applications in practice, but also because of interest from a fundamental point of view [1–6]. Despite their technological importance, the local structure of amorphous alloys (AMAs) as well as the diffusion processes involved cannot be regarded as being fully understood. One of possible mechanisms proposed for diffusion in AMAs presents a scenario in which atoms hop into vacancy or quasivacancy determined as a microscopic void. In addition, as-quenched AMA suffers from large number of vacancies in supersaturation which quickly annihilates upon relaxation. Consequently, the diffusion constant decreases and reaches a final value until the relaxation is over, for example, the system is transposed into a well-relaxed state [7, 8]. As such, the vacancy diffusion model enables the interpretation the relaxation effect which is observed experimentally in certain AMAs [9–13]. However, the stableness of vacancy is questioned for this model. Unlike the case of crystal, the neighbor-atom cages around vacancy are not structurally identical before and after atom hops into the vacancy. The consequent relaxation after atom jump may lead to the vacancy disappearing and finally all vacancies disappear. The molecular dynamic (MD) simulation could be used to test this question. In accordance with [14, 15], a vacancy introduced by removing some atoms from MD model disappears after one or several jumps indicating impossibility of vacancy mechanism. A logical supposition is that an elementary diffusion act will be accompanied with a large atomic arrangement around the vacancy. It results in disappearing the present vacancy, but also sometimes
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