Two intermetallic FeAl compounds with Al content of 70.68 and 72.17 at.pct were studied using Mossbauer spectroscopy (5 to 296 K) and X-ray diffraction (15 to 300 K). The compounds were found to crystallize in the orthorhombic Cmcm space group (eta-phase). The collected data revealed that dynamics of the Fe atoms (harmonic in entire temperature range) is significantly different that Al atoms. For the latter strong anharmonicity was evidenced. Moreover, it was found that partial filling of the different Al sites leads to occurrence of low and high symmetry coordination of Fe atoms, which was reflected in occurrence of two distinct doublets in Mossbauer spectra. All spectral parameters of the doublets as well as the Debye temperature, force constant, kinetic and potential energies of vibrations were determined. Those results revealed significant differences between both alloys, likely originating from approaching the stability boundary of the eta-phase for Fe-Al 72.17 at.pct alloy.
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