A new diffusion mechanism for self-compensating impurities in α-alumina

Abstract

Abstract Cation diffusion in α-alumina has been the subject of recent investigations, self-diffusion by the radiotracer technique and impurity diffusion by the SIMS technique. A review of the data is carried out to clarify the bulk diffusion mechanisms. Aluminium, cobalt, chromium, and yttrium exhibit a “normal” behaviour, which can be accounted for by an extrinsic vacancy diffusion mechanism. Silver, copper, and platinum behave as “fast diffusers”, although their activation energies are close to those of the other elements. From new experiments on magnesium diffusion reported in this paper, it is suggested that fast diffusion can be traced to self-compensating impurities. A diffusion mechanism which reconciles all the observations is proposed for these elements.