Infrared Spectra of Cubic and Tetragonal Manganese Ferrites

Abstract

AbstractThe infrared absorption spectra in the range from 200 to 700 cm−1 of cubic and tetragonal manganese ferrites, MnxFe3–xO4, are reported. An analysis of the spectra is made with a model by which the lattice vibrations are classified into species of the point group D2 d on the analogy of the results for gas molecules of equivalent symmetry. For cubic spinels with manganese concentrations x ≦ 1.0 the classification can be made according to the model of Waldron into the species of the point group Td. However, at 335 cm−1 an absorption has been observed which is out of the scope of the Td or D2 d classification, and which is caused by the substitution of a part of the octahedral Fe3+ ions by Mn2+ ions. The IR spectra of manganese ferrites with compositions 1 < x ≦ 3 can be analysed with the D2 d classification. The spectra of these materials do not change suddenly with the manganese concentration or with the crystal structure. From the splitting of the absorption bands in cubic ferrites with x > 1 it is concluded that there are local tetragonal distortions originating from the Jahn‐Teller effect of the octahedral Mn3+ ions.