It was recalled that atomic bond-deficiency was considered to be a deviation, from the coordination number of the ideal atomic structure, caused by chemical and topological short-range ordering. It was presented as being the characteristic structural defect in metallic glasses and deeply undercooled melts. Bond-deficiency defects were treated as being thermally inherent, and were based upon the notion of restricted rather than free atomic movement. They were formed under the short-range ordering constraint, and exhibited significantly smaller energy and volume costs when compared with crystal vacancies. Statistical thermodynamics were used to analyse binary systems where the formation of the critical bond-deficiency defects was related to the bond strengths and atomic sizes. Application to Zr-Cu, Zr-Ni and Zr-Be indicated that the experimentally observed glass transitions occurred at temperatures where a critical concentration of bond-deficiency defects was present. The dependence of the bond-deficiency defect concentration upon alloy composition agreed with experimental glass transition variations.

Atomic Bond Deficiency as a Structural Defect in Amorphous Metals - Relevance to Glass Transitions. A.Zhu, G.J.Shiflet, S.J.Poon: Acta Materialia, 2008, 56[3], 593-601

Table 17

Diffusivity of H in Zr-Alloys at 500C

*sol-gel encapsulated