Relation between the fine structure of the vibrational spectrum of the crystal lattice and the cation distribution in Co_1+2xFe_2−3xSb_xO₄ ferrites

Abstract

The infrared reflection spectra in the region of lattice vibrations (1500–200 cm⁻¹) of ferrite spinels Co_1+2xFe_2−3xSb_xO₄ with x=0.0–0.4 are investigated. The permittivity spectra are calculated using the Kramers-Kronig relations. A dispersion analysis of the ε₁(v); ε₂(v) spectra, carried out using the multiscintillator model, enabled the fine structure of the bands of the spectra to be determined. It was found that for CoFe₂O₄ ferrite the short-wave band (v=590 cm⁻¹) consists of two components, while the long-wave band (v=375 cm⁻¹) consists of fur components. Since cobalt ferrite is inverted spinel, in which there are only Fe³⁺ ions in the tetra positions, the doublet structure with v=590 cm⁻¹ must obviously belong to vibrations of the ion groups FeO₆ and CoO₆, while the second band may belong to vibrations of the ion complexes consisting of the tetra-cation (Fe³⁺), oxygen and the three closest octa-cations [3Fe], [2Fe1Co], [2Co1Fe] and [3Co]. The replacement of some of the iron ions with antimony leads to the appearance of additional lines from the short-wave edge of both bands. The intensity of these lines increases as the value of the diamagnetic substitution increases, which enables the highest-frequency component to be uniquely related to the vibrations of the complex formed by the tetra-cations Fe³⁺ or Co²⁺, the anion and the three octa-cations Sb⁵⁺.