Abstract
The Fe-Si binary system provides several iron silicides that have varied and exceptional material properties with applications in the electronic industry. The well known Fe-Si binary silicides are Fe3Si, Fe5Si3, FeSi, α-FeSi2 and β-FeSi2. While the iron-rich silicides Fe3Si and Fe5Si3 are known to be room temperature ferromagnets, the stoichiometric FeSi is the only known transition metal Kondo insulator. Furthermore, Fe5Si3 has also been demonstrated to exhibit giant magnetoresistance (GMR). The silicon-rich β-FeSi2 is a direct band gap material usable in light emitting diode (LED) applications. Typically, these silicides are synthesized by traditional solid-state reactions or by ion beam-induced mixing (IBM) of alternating metal and silicon layers. Alternatively, the utilization of organometallic compounds with reactive transition metal (Fe)-carbon bonds has opened various routes for the preparation of these silicides and the silicon-stabilized bcc- and fcc-Fe phases contained in the Fe-Si binary phase diagram. The unique interfacial interactions of carbon with the Fe and Si components have resulted in the preferential formation of nanoscale versions of these materials. This review will discuss such reactions.
Highlights
The Fe-Si binary phase system provides several compositionally distinct iron silicides that have diversely impressive electronic properties [1]
The thermodynamic stabilities of the various iron silicides will be discussed as a predictor for the propensity of the precursor materials to form the various iron silicides. This will be followed by the examples of various nanoscale iron silicides that have been formed from organometallic species, the products being listed in the order of their iron-richness; the iron-rich Fe3Si and Fe5Si3 examples being discussed initially, followed by the examples of the stoichiometric FeSi and, of the silicon-rich FeSi2 examples
In perusing the existing examples of known iron silicides, one may be tempted to predict that the prevalence or the paucity of a particular iron silicide is an outcome of its thermodynamic stability, which happens to be the case to a large extent
Summary
The Fe-Si binary phase system provides several compositionally distinct iron silicides that have diversely impressive electronic properties [1]. During solid-state reactions of the (Fe,Si) couple, FeSi has been predicted to form as the first silicide, among the possible iron silicide products, due to its favorable ΔGv (the change in free energy per unit volume or the driving force for nucleation) characteristics [38]. This prediction was corroborated by the formation of FeSi as the first phase in amorphous deposited elemental layers of silicon and iron in a thin-film diffusion couple during thermal annealing [40]. This will be followed by the examples of various nanoscale iron silicides that have been formed from organometallic species, the products being listed in the order of their iron-richness; the iron-rich Fe3Si and Fe5Si3 examples being discussed initially, followed by the examples of the stoichiometric FeSi and, of the silicon-rich FeSi2 examples
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