Microscopic environment of Fe in epitaxially stabilized c-FeSi

Epitaxially stabilized iron monosilicide films having the CsCl structure (c-FeSi) have been investigated by conversion electron Mossbauer spectroscopy and transmission electron microscopy. The Fe-57 Mossbauer parameters (isomer shift delta, linewidth Gamma, and quadrupole splitting Delta) are reported and discussed in terms of the local surrounding of the Fe nucleus. High statistical accuracy and resolution allowed a detailed investigation of the effects of strain and of the structural phase transformation from the epitaxially stabilized to the bulk stable phase, The phase transformation was found to proceed in a rather surprising layer by layer mechanism with smooth interfaces between the epitaxially stabilized, the bulk stable, and a third phase. Results from a molecular-dynamics simulation at constant pressure and temperature of the structural phase transition are presented and compared with the experimental findings. The isomer shift and the electric-field gradient at the Fe nucleus in the strained c-FeSi and in the third phase have been calculated using the ab initio full potential linear muffin-tin orbital method. The Mossbauer parameters of some relevant point defects in c-FeSi have likewise been calculated within this framework. [S0163-1829(99)01302-8].