Non- classical diffusion processes

This paper surveys quantum effects in diffusion, with special emphasis on isotope effects for hydrogen isotopes in metals. The various possible contributions to the isotope effect are surveyed, and their importance assessed. The bcc metals (V, Nb, Ta) and fee metals (Cu, Ni, Pd) involve different mechanisms, and these are still doubts in detail about some aspects. A full understanding requires knowledge of the hydrogen-metal interactions. Recent theoretical work supports some of the qualitative ideas discussed, and offers promise for future analyses.