Influence of the Preparation Method and Magnesium Ions Substitution on the Structure and Magnetic Properties of Lithium-Iron Ferrites

Abstract

In this work, magnesium-substituted lithium-iron spinels were synthesized by two methods: sol–gel auto combustion and ceramic. Conducted X-ray, Mössbauer, and impedance studies have shown the advantages of the sol–gel method of auto combustion. It was found that sol–gel synthesis leads to nano disperse particles with higher porosity, higher value of the lattice constant, and the degree of stoichiometry of lithium than in systems, synthesized by ceramic method. The samples obtained by sol–gel method have a more perfect structure and are highly stoichiometric. The results obtained in this work confirmed the fact that the reduction in part size leads to a dominant contribution of the particle surface, which significantly changes the properties of the synthesized material. Studies of the conductive and dielectric properties of magnesium-substituted lithium-iron spinels based on impedance spectroscopy have shown that the studied systems are characterized by the presence of two conduction mechanisms: electronic and ionic; electronic conductivity is based on the jumping mechanism due to the presence of ferrous ions and is realized mainly by the volume of grains in the octa-sublattice of spinel. With increasing number of ions of substituted magnesium for systems synthesized by ceramic method, the value of conductivity at direct current does not change due to participation in the hopping mechanism of stable complexes $\left[ {{\text{Li}}_{{{\text{tetra}}}}^{ + } {\text{Fe}}_{{{\text{octa}}}}^{3 + } } \right]$, formed during substitution. The obtained results showed the expediency of using the sol–gel method of auto combustion for the synthesis of high-quality nanosized ferrites with improved technological characteristics.