Nanocomposites FeCoNi/C based on polyvinyl alcohol: synthesis and electromagnetic properties

Abstract

Triple FeCoNi nanoparticles distributed and stabilized in the carbon matrix of FeCoNi/C metal-carbon nanocomposites were synthesized. The synthesis of nanocomposites was carried out by controlled IR pyrolysis of precursors of the "polymer-metal nitrates" type, obtained by joint dissolution of the components with subsequent removal of the solvent. The effect of the synthesis temperature on the structure, composition, and electromagnetic properties of nanocomposites has been studied. It was shown by XRD that the formation of ternary FeCoNi nanoparticles occurs through the dissolution of Fe in the nanoparticles of the NiCo solid solution. With an increase in the synthesis temperature, the size of metal nanoparticles increases, which is determined by the processes of their agglomeration and coalescence during matrix rearrangement. Also, depending on the synthesis temperature, nanoparticles of a ternary alloy with different compositions can be formed, and the ratio of metals specified in the precursor is achieved at 700 °C. By Raman spectroscopy was shown  that, with an increase in the synthesis temperature, the degree of crystallinity of the carbon matrix of nanocomposites increases, and graphene structures consisting of several layers can be formed. The frequency dependences of the relative complex dielectric and magnetic permeabilities of nanocomposites in the range of 3–13 GHz were studied. It is shown that an increase in the synthesis temperature causes a significant increase in both dielectric and magnetic losses (~ 2 times). The former are associated with the formation of a complex nanostructure of the carbon matrix of the nanocomposite, while the latter are determined by an increase in the size of nanoparticles and a shift of the EFMR frequency to the low-frequency region. Reflection loss (RL) calculations were performed according to the standard procedure based on experimental data of the frequency dependences of the complex magnetic and dielectric permittivity. It was shown that control of the frequency range and absorption value of electromagnetic waves (from 50 to 94%) can be carried out by changing the temperature of synthesis of nanocomposites.