Sol–Gel Synthesis of Nanodispersed Solid Solutions Based on Sr_xBa_{(1 – x)}Fe₁₂O₁₉ Barium Hexaferrite

Abstract

This paper studies the application of the sol–gel method in the synthesis of M-ferrite of the composition Sr_xBa_{(1 – x)}Fe₁₂O₁₉ (х = 0, 0.3, 0.5, 0.7, 1). The synthesis procedure is based on preparing a gel from citric acid and barium, strontium, and iron nitrates, its calcination at 500°C, mechanochemical activation, and recalcination at 700°C. The target product is a dark brown powder; it was studied using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, and differential scanning calorimetry (DSC). The single-phase state of the synthesized samples has been confirmed by powder X-ray diffraction. Examination of the X-ray diffraction patterns of the synthesized hexaferrites and the X-ray diffraction patterns of the ICDD reference compounds reveals that all diffraction peaks coincide. The unit cell parameters of the samples calculated from X-ray diffraction patterns depend linearly on the degree of substitution of barium in hexaferrite according to the Vegard rule for solid solutions, which confirms the successful substitution of barium ions for strontium ions in the structure of barium hexaferrite. The morphological parameters of the particles of the obtained solid solutions were studied using SEM. Examining the electron microscopic images shows that particles of an average size of 50 nm formed in all the solid solutions. The average size of the coherent scattering regions, as calculated by the Scherrer equation, was 25 nm. The regular hexagon faceting characteristic of hexaferrite particles cannot be observed in SEM images because these particles are too small. Mapping of the images indicates a high level of homogenization of the initial reagent under the selected synthesis conditions. DSC yielded the values of the Curie temperature for each level of substitution with the Curie temperature increasing with the substitution level.