Mössbauer and X-ray data on β-FeOOH (akaganéite)

Abstract β -FeOOH (akaganéite) was prepared by slow hydrolysis of an FeCl 3 solution. X-ray diffraction measurements gave refined unit-cell parameters of a =10·535 Å, c =3·030 Å. Two doublets with δ (Fe)=0·39, ΔE Q =0·95, and δ =0·38, ΔE Q =0·55 mm s −1 , respectively, can be fitted to the Mössbauer spectrum taken at room temperature. Magnetically split Mössbauer spectra were registered at 135 and 4°K. These can be resolved into at least three superimposed sextets, corresponding to different Fe 3+ sites in the β -FeOOH structure. At 4°K a three sextet model gives parameters of δ =0·36, ΔE Q =0·90, H i =473; δ =0·35, ΔE Q =0·30, H i =479; and δ =0·37, ΔE Q =−0·05 mm s −1 , H i =486kOe, respectively. The complexity of the Mössbauer spectra of β -FeOOH limits the usefulness of this method as a tool for the identification of akaganéite in composite natural samples.