Nanostructured α-Fe2O3 powders were prepared by high-energy ball milling.
The milling process spans grinding times from 30 min to 24 h. The as-milled samples were
characterized by means of 57Fe Mössbauer spectrometry, Rietveld analysis of X-ray
diffraction data and particle size analysis. The obtained results evidence the presence of
disordered hematite characterized by a hyperfine field distribution with a well-behaved
dependence on the mean crystallite size for which the mean hyperfine field decreases
asymptotically as the grain size decreases. A new relationship is proposed in order to
describe such behavior. Finally the presence of superparamagnetic grains, the occurrence of
a partial topotactic phase transformation into a spinel phase and tool induced contamination
are also presented and discussed. |
