Mössbauer-effect and x-ray-absorption spectral study of sonochemically prepared amorphous iron

Abstract

The Mössbauer spectra of amorphous iron, prepared by using sonochemical methods, exhibit a broad magnetic hyperfine sextet at both 78 and 295 K. The spectra do not change with time if the amorphous iron is not exposed to oxygen or moisture. An analysis of the spectra with the method of Lines and Eibschütz yields average magnetic hyperfine fields of 29.1 and 25.9 T at 78 and 295 K, respectively. The corresponding moments of 1.9 B and 1.7 B agree well with values obtained from earlier magnetization studies and, further, provide strong experimental support for earlier calculations of the magnetic moments in amorphous iron. The observed average isomer shifts of 0.27 and 0.14 mm/s obtained at 78 and 295 K, respectively, correspond to a decrease in the s-electron density at the iron-57 nucleus as compared to that of ␣-iron, a decrease which is consistent with the decreased coordination number of amorphous iron. The similarity of the 295 K iron K-edge x-ray-absorption spectrum of amorphous iron and ␣-iron, up to 7130 eV, indicates that the d-electron density of states just above the Fermi level is similar in both forms of iron. The absence of structural details above 7130 eV in the spectrum of amorphous iron indicates, in agreement with multiple-scattering calculations, that long-range order does not extend beyond the third shell of neighbors in amorphous iron. Greatly reduced extended x-ray-absorption-fine-structure scattering is observed at the iron K edge of amorphous iron as compared to ␣-iron. An analysis of the weak observed scattering reveals both a decrease in the average coordination number from 14 in ␣-iron to 10 in amorphous iron, and an asymmetric radial distribution function of the iron neighbors in the first shell. This asymmetric distribution yields for amorphous iron a minimum iron-iron distance of 2.40 Å and an average iron-iron distance of 2.92 Å. ͓S0163-1829͑98͒08817-1͔

Ion Beam Formation and Modification of Cobalt Nanoparticles

“…This spectrum is also similar to that reported previously for thin-film amorphous Co [66]. The changes in the a-Co NP XANES spectra (compared to the c-Co NPs and bulk HCP Co) are consistent with those observed for other transition metals including Cu NPs [67] and bulk amorphous Fe prepared sonochemically [65]. The observed changes are attributed to the disappearance of multiple scattering (MS) features and shape resonances associated with these MS paths in the amorphous phase.…”

“…The prominent features of the bulk HCP Co and c-Co NP spectra in Figure 10 result from multiple scattering resonances of the 1s photoelectron [20]. The a-Co NP spectrum (and those of disordered or amorphous materials in general) exhibits less fine structure due to the loss of such multiple scattering contributions [45,65]. This spectrum is also similar to that reported previously for thin-film amorphous Co [66].…”

The influence of thermal annealing on structure and oxidation of iron nanowires

“…= 0.03 mm/s; (iii) a smeared component being characterized by high values of magnetic hyperfi ne fi eld (over 34 T). The fi rst component represents crystalline -Fe, while the second one is attributed to an amorphous iron-based phase which possibly contains some contribution of oxygen atoms [10]. The last component, because of high values of magnetic hyperfi ne fi eld, is attributed to iron oxides which are situated probably at the surface of the nanowires and thereby they are distorted and characterized by many different values of magnetic hyperfi ne fi eld.…”

Surface decoration of amine-rich carbon nitride with iron nanoparticles for arsenite (AsIII) uptake: The evolution of the Fe-phases under ambient conditions

“…6a,b). The resulting hyperfine Mössbauer parameters (MP) listed in Table 1, correspond to amorphous, for M1, and crystalline (bcc) for M2 metallic (Fe • ) iron nanoparticles [39]. The central part of the spectrum is covered by a quadrupole split contribution (component P1 in Table 1, green line in Fig.…”