Mechanical alloying of Si and Fe: Quantum-mechanical calculations applied to Mossbauer and X-ray diffraction studies

Hyperfine parameters of iron nuclei such as isomer shift, quadrupole splitting, and asymmetry parameter are calculated for beta-FeSi2 with and without vacancies, using density functional theory. They are applied, in combination with parameters of alpha-FeSi2 obtained earlier, for analyzing Mossbauer and X-ray diffraction experiments on the mechanical alloying of silicon with iron in the range of 1-33 at.% of Fe. Such an approach allows more detailed and precise information to be obtained on the structure of Fe-Si samples. In particular, the fraction of vacancies in alpha- and beta-FeSi2 is estimated, and the mechanism of formation of these phases and their transformation into each other is discussed. A new model is developed for analyzing experiments on hyperfine interaction, such as Mossbauer spectroscopy, time-differential perturbed-angular correlation, and the like, for Fe-Si systems with a high Si content.