Monte Carlo Simulation of Correlation Effects in a Random SC Alloy via Interstitialcy Mechanisms

In this paper some recent progress in the area of Monte Carlo simulation of diffusion via the interstitialcy mechanism in a randomly ordered binary alloy is reviewed. Topics discussed include the calculation of tracer correlation factorsfA and fBas a function of composition and jump frequency ratiowA/wBand interstitialcy correlation factors fI; which play a crucial role in the interpretation of ion-conductivity data. The percolation behavior of fI when wA ≪ wB is analysed in detail and limits of the tracer diffusivity ratios bD A/bD B for alloy compositions below thepercolation threshold are presented. Allowance for non-collinear jumps (partly) replacing concurrent collinear site exchanges leads to a reduction of diffusion correlation effects.This goes along with a shift of the diffusion percolation threshold to lower concentrations of the (more) mobile component B. Even stronger changes of mass and charge transport compared to an exclusively collinear interstitialcy scheme are observed for additional contributions of direct interstitial jumps. It is remarkable that for both extensions of interstitialcy-mediated diffusion the Haven ratio appears to be greater than unity in certain compositionranges poor in B.