Impact of Co and Mn substitution on structural and dielectric properties of lithium soft ferrites

Abstract

Co2+ and Mn2+ co-doped lithium spinel ferrites with the chemical composition Li0.5Fe2.5-0.5xCoxMnxO4 (x = 0.0–0.5) were fabricated by micro-emulsion method. The spinel structure with face centered the cubic phase was confirmed from the XRD study. The lattice constant was found to increase first from 8.369 to 8.374 Å and then decreased up to 8.367 Å, as the substitution level increased, attributed to the formation of the secondary phases. The crystallite size of nano ferrites was found in the range of 47 to 37 nm. Substitution of Co2+ and Mn2+ significantly enhanced the density of prepared ferrites. FTIR studies revealed the appearance of the characteristic vibration bands of Li0.5Fe2.5O4 between 550 and 650 cm−1 which were appreciably influenced by the concentration of Co2+ and Mn2+. The force constants showed an indirect variation with the bond lengths of A- and B -sites. The dielectric properties such as dielectric constant (εʹ), complex dielectric constant (εʹʹ) and tangent loss (tanδ) were analyzed between 1 MHz and 3 GHz. By increasing the frequency, εʹ, εʹʹ, and tanδ were decreased and have shown a dispersive behavior at higher frequencies due to the effect of space-charge polarization. The obtained low values of dielectric loss may refer these materials for applications in transformer cores and high-frequency devices.