A High-Temperature Mössbauer Study of the Iron Nitrides

Mössbauer spectra of the iron nitrides have been measured at room temperature and at 550°C. In the case of the room temperature spectrum of γ ′-Fe 4 N, a fit strategy is reviewed which accounts for two spectroscopically inequivalent iron Fe(1) sites due to the simultaneous presence of magnetic and quadrupolar interactions. In contrast, the high-temperature spectra of γ ′-Fe 4 N allow for the direct determination of the quadrupolar interactions at Fe(1) sites. In the case of ɛ -Fe 3 N 1+ x , the stoichiometry dependent magnetically-split room temperature spectra demonstrate the extensive ordering of nitrogen in the compound. At 550°C, spectra have been measured at various defined thermodynamic conditions of controlled nitrogen activity. The quadrupole-split spectra high-temperature are discussed in relation to structure and disorder of the material. In particular, it is shown that the composition dependent high-temperature spectra of ɛ -Fe 3 N 1+ x can be modelled in the framework of a simple two-site model.