Al‐for‐Fe substitution in hematite: the effect of low Al concentrations in the Raman spectrum of Fe₂O₃

Five different mixed Al‐hematites with an aluminium molar content varying from 0 to 10% were investigated by micro‐Raman spectroscopy to study the effect of Al‐for‐Fe substitution on the hematite lattice. A red shift of hematite vibrational wavenumbers and a line broadening were observed; also a shoulder located near 430 cm −1 and a broad band at 670 cm −1 developed. The variation of the spectral features is discussed in terms of a local disorder correlated to the insertion of Al 3+ ions into the Fe(O) 6 octahedra constituting hematite structure. A multivariate analysis was also carried out on the spectral data to distinguish between the doped samples analysed.