Data about the spectral shifts for ferrite-spinels which contain Fе$^{3+}$ ions in both cation sublattices may be used to acquire the values of the oxygen parameter u and its changes caused by different factors. The basis of this method is a formalism from the theory of molecular orbitals which makes it possible to quite precisely calculate the dependence of the contributions to spectral shifts caused by "covalency effects" on the cation to anion distances in the structure of the spinel. A correlation of change in the difference in the shifts of partial spectra and internal reordering of the structure with a preservation of symmetry is established.
Department of General Physics for the Physics Faculty, Faculty of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia
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