Determination of the hyperfine parameters of iron silicides by angle dependent conversion electron Mössbauer spectroscopy on single crystals

Iron silicides are of growing interest because of their interesting properties in reference to potential applications in thermoelectrics, photovoltaics and optoelectronics. For phase analysis by Mössbauer spectroscopy on bulk material or on thin layers, the knowledge of their hyperfine parameters is necessary.
In the present study, the Mössbauer spectra of single crystals of various silicides e-FeSi, ß-FeSi2 and a-FeSi2 are collected by conversion electron Mössbauer spectroscopy at room temperature. Measurements were performed at different angles between the propagation direction of the exciting g-radiation and the crystal axis of the single crystals.
The Mössbauer spectrum of the monosilicide consists of two lines while those of the disilicides consist of four lines. In the latter two cases, an unambiguous assignment of the lines to two quadrupole doublets could be performed. The hyperfine parameters including the signs of the quadrupole splittings are determined with high accuracy. Moreover, the direction of the main axis of the electric field gradient in regard to the crystal orientation was determined.
The results are compared with those obtained at powder or thin layer samples in the past. Differences and coincidences are discussed.