Explicit studies of the quantum theory of light interstitial diffusion

The formalism associated with small-polaron diffusion in the high temperature semiclassical regime (valid above some fraction, < approximately 1/3, of the Debye temperature) is generalized so as to transcend existing simplifications. The diffusion constant is then calculated for simple models in which the metal atoms interact with each other and with the interstitial atom with two-body forces. Studies of these models not only confirm the necessity of generalizing the formalism but also yield diffusion constants whose magnitudes and temperature dependences are consistent with the general features of the existing data for the diffusion of hydrogen and its isotopes in bcc metals. The motion of a positive muon between interstitial positions of a metal is also investigated. In particular, the muon is regarded as an especially light isotope of hydrogen; that is, the interaction parameters used to model hydrogen diffusion are retained to model muon motion. (Auth.)