Characterization of FeOOH polymorphs and ferrihydrite using low-temperature, applied-field, Mössbauer spectroscopy

Abstract

A B S T R A C T:M6ssbauer spectroscopy obtained with the sample at low temperatures and subject to large magnetic fields is discussed in terms of its use in analysing the naturally occurring polymorphs of FeOOH and the common growth precursor, ferrihydrite. Experiments on well-characterized synthetic samples provided benchmark results. A relatively simple means of quantitative analysis was used, in which sextets of Voigtian-shaped lines were summed and least-squares fitted. The results are discussed in terms of the magnetic structures of each compound.Fine-grained iron oxides and oxyhydroxides in soils and sediments can often be best identified using M6ssbauer spectroscopy, since their X-ray diffractograms are complicated by small crystallite size-broadening and the iron phases may constitute a relatively small proportion of the sample. Several excellent reviews of the work have been published

Geochemistry of iron and manganese in soils and sediments of a mangrove system, Island of Pai Matos (Cananeia — SP, Brazil)

“…Comparison of these values with the site 3 values shown in Table 2, indicates that site 3 (18%) could be assigned to ferrihydrite. Previous MS studies of goethite show that both Al 3+ substitution for Fe 3+ and crystallinity reduce the magnetic hyperfine field (de Oliveira et al, 1996;Pollard et al, 1992). Sites 3 (18%) and 4 (11%) could be also assigned to goethite ( Table 2).…”

Recognizing sulfate and phosphate complexes chemisorbed onto nanophase weathering products on Mars using in-situ and remote observationsk

“…Mössbauer measurements of nanophase iron oxides at low temperatures can reduce the effects of small particle size and isomorphous substitution on the spectra so that they display a sextet instead of a doublet and nanophase iron oxides can be distinguished from one another (e.g., Pollard et al 1992). Two-line ferrihydrite, as was studied here, displays a sextet in Mössbauer data when measured at extremely low temperatures (i.e., 4.2 K; Pollard et al 1992); however, ferrihydrite displays a doublet at 77 K (Pollard et al 1992). As such, we would not expect a sextet in Mössbauer data of ferrihydrite on Mars, so the Mössbauer spectra collected here are similar to those that would be collected on the martian surface.…”

Magnetic dynamics of weakly and strongly interacting hematite nanoparticles

“…The parameters corresponding to the peak positions of this component are B hf ϭ48.5Ϯ1.0 T, ␦ϭ0.48Ϯ0.02 mm s Ϫ1 , and ⑀ϭϪ0.05 Ϯ0.02 mm s Ϫ1 and they correspond well to those reported for 6-line ferrihydrite. 34,35 B. Mössbauer spectra of the coated sample Mössbauer spectra of the coated sample were obtained at temperatures up to 240 K. Higher temperatures lead to a significant reduction of the Mössbauer effect because the melting point of the ice matrix is approached. Representative spectra are shown in Fig.…”