Mössbauer effect study of the Β-FeOOH to α-Fe2O3 phase transformation

Β-FeOOH was precipitated from a chloride solution. Mossbauer spectra were taken at room temperature (RT) and at 4.2 K in zero field and in external magnetic fields. Samples aged for successively longer time periods were studied. They contain α-FeOOH and α-Fe2O3, the Mossbauer spectra of which show superparamagnetic behavior. The transformation into α-Fe2O3 is already induced by aging in the mother solution at 100 ‡C. A final heat treatment at 350 ‡C leads to the complete transformation into α-Fe2O3 and to an increase of the crystallite size.