Monte Carlo simulations of Mossbauer spectra in diffusion investigations

We study the diffusion process via a vacancy mechanism in an A-B binary all oy with B2 order. The starting point of our Monte Carlo simulations were ex periments done recently by Mossbauer spectroscopy and nuclear resonant scat tering on stoichiometric B2 ordered FeAl, which yielded a nonobvious jump m odel for the Fe atoms, namely a priority of effective jumps to third-neares t-neighbor sites over second-nearest-neighbor sites. In the simulations we chose ordering energies that ensured a phase diagram close to that of the r eal Fe-Al system. Allowing the vacancy to exchange with nearest-neighbor at oms exclusively, we obtained a perfect agreement between simulation and exp eriment for the case when an interaction between the vacancy and the atoms was included. We suggest that the remarkable features of Fe diffusion arise from highly correlated vacancy paths, which are due to an interaction of t he vacancy with locally disordered areas in the B2 lattice created by the v acancy movement itself. [S0163-1829(99)10113-9].