New direct method for evaluating recoilless f-factors of two iron-sites in Fe-bearing compounds using Mössbauer spectrometry Available to Purchase

We propose a new direct method for calculating simultaneously two recoilless f-factors of any iron-bearing compound relative to that of a reference material by collecting only a single-temperature Mössbauer spectrum. This methodology is comparatively much simpler than the usual one which requires taking Mössbauer spectra of the compound at several temperatures and subsequently fitting the temperature dependence of the subspectral area or the isomer shift data with a lattice vibrational model. We demonstrate the applicability of this new methodology in the case of three common iron-bearing compounds: magnetite, akaganeite and goethite, but of course this type of study can be extended to other materials. The two f-factors for each compound were related to iron ions located in sites of different origin: for magnetite, these were related to irons with two different oxidation states; for akaganeite to irons in two different crystallographic sites; and for goethite to irons in similar crystal sites but located in grains of different sizes. In the case of magnetite, we found that the f-factors for the Fe³⁺ and Fe^2.5+ sites relative to that of metallic iron powder were of f_Fe³⁺/f_Fe = 0.97 ± 0.05 and f_Fe^2.5+/f_Fe = 0.92 ± 0.05, respectively. Interestingly, the quotient of these two f-factors, i.e., f_Fe^2.5+/f_Fe³⁺, is equal to 0.95 ± 0.05, which compares fairly well with a value reported in literature obtained using the complex methodology based on the temperature dependence of the absolute subspectral area and the Debye approximation. For akaganeite, the f-factors of the doublet 1, D1, and doublet 2, D2, sites relative to that of metallic iron powder were of f_D1/f_Fe = 0.95 ± 0.08 and f_D2/f_Fe = 0.98 ± 0.15, respectively. And for goethite we found that the f-factors of the sextet 1, G1, and sextet 2, G2, sites relative to that of metallic iron powder were of f_G1/f_Fe = 0.80 ± 0.02 and f_G2/f_Fe = 0.80 ± 0.02, respectively. The similarity of these last two factors is perhaps due to a sharp distribution of large grains.