Correlation effects for interstitial-type self-diffusion mechanisms in b.c.c. and f.c.c. crystals

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Abstract
The tracer correlation factor, the quasi-elastic neutron scattering and the Mössbauer line broadening have been investigated in terms of the encounter model for a number of interstitial-type self-diffusion mechanisms in f.c.c. and b.c.c. crystals. In particular, the migration of (100) dumb-belle in the f.c.c. lattice and both the two- and three-dimensional migration of (110) dumb-bells in the b.c.c. lattice have been considered. From a comparison with similar calculations for vacancy-type mechanisms in both the f.c.c. and b.c.c. lattices, it is concluded that (1) the differences in the predicted correlation effects between monovacancy and dumb-bell interstitialcy mechanisms are substantial, but that (2) experiments aiming at distingusihing between the divacancy and dumb-bell mechanisms via correlation effects may not be very useful because of the rather small differences predicted. Our results are compared with recent experiments in solid sodium by means of quasi-elastic neutron scattering (Göltz et al. 1980) and nuclear spin relaxation (Brünger et al. 1980) and with the radiotracer results of Mundy (1971).