Quantum Theory of Diffusion with Application to Light Interstitials in Metals

Abstract

A quantum theory of diffusion is presented and applied to the particular problem of light interstitial diffusion. The theory focuses attention on transitions among approximate localized eigenstates of the system. The diffusion rate of a light interstitial in bcc metals is shown to be determined principally by the self-trapping distortion which stabilizes the impurity at a particular interstice. A quantitative explanation of both the motion energy and the motion entropy follows from the theory. The differences between interstitial motion in bcc and fcc hosts, and also the dependence of the diffusion rate on isotopic mass, are discussed.