A second binding model to study diffusion of $Cr$ diluted in BCC $Fe$

A classical molecular static technique (CMST) and DFT calculations using SIESTA, are employed here to characterize the self diffusion and the tracer solute diffusion in the bulk of BCC diluted $FeCr$ alloy driven by both vacancy and interstitial migration. For the first time in the literature, a six-frequency model (developed by Okamura and Allnatt) involved in a second nearest neighbor binding approach is adapted for calculations in a real system. We obtain microscopic parameters, namely: i) the free energy of vacancy formation and the vacancy-solute binding energy, ii) the involved jump frequencies, and iii) the tracer correlation factor. The present approximation describes much better the experimental data of self and solute atoms than recent calculations using a first binding approach. Also, we confirm that a vacancy drag mechanism is unlikely to occur in $FeCr$ diluted alloys. Our results also show that the diffusion processes is mainly mediated by vacancies, while diffusion by intertitial mechanism is several orders of magnitudes slower.

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