Super-abundant vacancies were the vacancies of M atoms formed in M–H alloys, in concentrations as high as 30at%. The results of super-abundant vacancy formation, as revealed by X-ray diffraction at high temperatures and high H pressures, and its mechanism in terms of vacancy-H (V-H) cluster formation were described, including the underlying information of V-H interactions. One of the most important conclusions of the theory was that defect structures containing super-abundant vacancies were in fact the most stable structure of M–H alloys, and therefore super-abundant vacancies should be formed whenever the kinetics allowed. It was subsequently shown that super-abundant vacancies could be formed in the process of electrodeposition. Some of the consequences of super-abundant vacancy formation including the enhancement of M-atom diffusion and creep were described, and its possible implication in the H embrittlement of steels was mentioned.

Formation of Superabundant Vacancies in M–H Alloys and Some of its Consequences - a Review. Y.Fukai: Journal of Alloys and Compounds, 2003, 356-357, 263