Infrared studies of spinels-III. The normal II-III spinels

In accordance with theoretical expectations, 4 bands are generally observed in the i.r. spectrum of a number of cubic normal II-III spinels. The systematic investigation of pure compounds, solid solutions and isotopic species leads to a realistic and consistent set of assignments: the 2 high-frequency bands v1 and v2 essentially depend (in shape and position) on the chemical nature of the octahedral, trivalent cation and thus are essentially related to vibrations of the lattice of octahedral groups. The 2 low-frequency bands v3 and v4 must be assigned to complex vibrations involving the simultaneous participation of both cations, tetrahedral and octahedral. This complex origin is definitely demonstrated by the study of isotopic species. These assignments, which are in accordance with all the experimental data collected on normal II-III spinels, cannot be extended to other types of spinels (inverse II-III, normal II-IV,⋯). © 1971.