Nuclear spin relaxation by translational diffusion in solids. IV. Two-spin systems in FCC crystals and third-nearest-neighbour jumps on a SC lattice

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Abstract
For pt.III see ibid., vol.9, p.4315 (1976). The two-spin systems describe the dipole-dipole interactions between stationary host spins and spins migrating amongst either the tetrahedral or the octahedral interstitial sites. The tetrahedral sites in a FCC crystal form a SC lattice and two models, the symmetric and asymmetric jump models, are considered for third-nearest-neighbour jumps on this lattice. Numerical results for the correlation functions relevant for single crystals and polycrystals are presented over the entire temperature range. It is found that the simpler, but unphysical, symmetric jump model is a good approximation to the more complicated asymmetric jump model. Discrepancies between the numerical results of Barton and Sholl and those of Wolf (1975, 1977) are discussed.