Synthesis, structural, optical, electrical and Mössbauer spectroscopic studies of Co substituted Li_0.5Fe_2.5O₄

A series of cobalt substituted lithium ferrite Li_0.5Co_xFe_2.5−xO₄ with x=0, 0.2, 0.4 was prepared by a chemical technique called citrate precursor method. In this technique citric acid was used as a reducing agent. Structural, morphological, topographical, optical, electrical, and magnetic properties were studied by using X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, DC resistivity, Mössbauer Spectroscopy. XRD patterns showed characteristic (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0) peaks which confirmed the inverse spinel phase. SEM and TEM support the formation of cubic nanoparticles. FTIR studies reported the ferrite peaks between 400 cm⁻¹ and 800 cm⁻¹ confirming the inverse spinel structure. Five optical Raman modes (A_1g+E_g+3F_2g), characteristics of the cubic spinel structure with (P4₃32) space group are also observed. Electrical DC resistivity studied from room temperature to 300 °C showed the semiconducting behavior of lithium ferrite. Porosity, transition temperature and activation energy are found to decrease with cobalt ion concentration. The room temperature Mössbauer spectra of all the samples showed normal Zeeman Splitting sextets supporting the formation of ferromagnetic phase. With increase in cobalt content, the value of hyperfine field at A site is found to vary from 53.15 to 54.96 T whereas at B site it vary from 54.79 to 52.82 T. The obtained results have been explained based on possible mechanisms, models and theories. - Highlights: • XRD studies confirmed the spinel structure. • In FTIR studies, two frequency metal oxide bands are observed. • Raman spectra confirmed the symmetric and anti-symmetric band position. • Mössbauer spectroscopy reveals the two magnetic sextets.