MOSSBAUER-EFFECT AND POSITRON-ANNIHILATIO N IN IRON SILICIDES

The electron density redistribution between Si and Fe atoms in the FeS i, beta-FeSi2, and alpha-FeSi2,3 compounds as well as the influence of structural vacancies upon charge transfer between alloy's constituent s has been studied by means of Mossbauer and positron spectroscopies. The isomer shift, delta E, for FeSi and beta-FeSi2 was found to be of 0.08 mm/s refered to that of alpha-iron, whereas for metallic alpha-Fe Si2,3 phase its value amounts to 0.30 mm/s. The positron affinity to t he Fe atoms in alpha-phase decreases and an 30% increase of probabilit y of annihilation with quasi-free electrons is observed compared to th ose of semiconducting beta-phase. These changes indicate the localizat ion of 3d-electrons at Fe atoms due to the high concentration of struc tural vacancies resulting in the break of covalent Fe(3d) - Si(3p) bon ds.