Ferrihydrite Mossbauer spectrum

Murad, E. and Schwertmann, U. (1980) The MOssbauer spectrum of ferrihydrite and its relations to those of other iron oxides. Amer. Miner. 65 1044-1049. 

Influence of Tetravalent Cations The influence of the Ti ion presence during the formation of goethite from ferric solution in an alkaline medium was investigated by Mossbauer spectroscopy and other techniques [246]. The presence of Ti " " ions partially suppressed the transformation of ferrihydrite to goethite and as a result a quadrupole doublet, corresponding to the low-crystalline phase, emerged in the Mossbauer spectrum. 

Fig. 3.7 Mossbauer spectrum of ferrihydrite at RT fitted with two doublets (left) and at 4 K fitted with a (5-correlated hyperfine field distribution (right)...

However, several more recent works have resulted in a complete change in the earlier, more-or-less contradictory ideas about ferrihydrite and its XRD and Mossbauer behavior. Berquo et al. [72] report the possibility of synthesizing Si-ferrihydrites with much better crystallinity. One of the authors ferrihydrites shows even relatively sharp lines in the XRD pattern and its Mossbauer spectrum even consists of a somewhat collapsed sextet at RT, but with no doublet contribution. The spectrum of a natural sample, showing similarly seven, but somewhat broadened lines in the XRD pattern, exhibits a collapsed sextet at 130 K, but remains exclusively a doublet at RT. 

Another example concerns the Mossbauer measurement of iron-containing nodules in a planosol from the S-W Ethiopian highlands [270]. The RT Mossbauer spectrum of the nodules in the vertic horizon as well as that of the accumulated nodules consists of a single doublet at RT, which converts partly into a goethite sextet at 80 K (Fig. 3.43). The remaining Fe " doublet with a quadrupole splitting of 0.60 mm/s might be attributed to ferrihydrite. 

E. Murad, The Mossbauer spectrum of well -crystallized ferrihydrite. J. Magn. Magn. Mater. 74, 153-157 (1988)... 

Other physical properties also show that the iron cores of native ferritins and bacterioferritins are different. Mossbauer spectra of ferritins measured as a function of temperature (Fig. 1) show quadrupole split doublets, with an isomer shift typical of Fe +, gradually being replaced as the temperature is lowered (between about 50 and 15 K) by a magnetic hyperfine spectrum (30, 31). The transition temperature, Tb, is lower than the ordering temperature, Tord (240 K) observed for bulk ferrihydrite (32), because of fluctuations in the direction of mag-... 

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