Correlation effects in atom transport by the interstitialcy mechanism

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Abstract
Diffusion by the interstitialcy mechanism is studied for a hexagonal lattice of two interpenetrating triangular lattices of substitutional and interstitial sites. The tracer correlation factor is calculated exactly in the limits of low and high interstitial concentrations by the use of lattice Green function properties, a convenient extension of a method which has proved powerful for vacancy models. Monte Carlo simulations are presented for the same model over the complete concentration range; the concentration dependence is qualitatively different from that already known for the interstitialcy mechanism on the square planar lattice. Simulations have also been made at low concentrations for the same model modified by the presence of clusters of blocked sites which take no part in the migration process.