One-pot synthesis of hard/soft SrFe10O19/x(Ni0.8Zn0.2Fe1.8Cr0.2O4) nanocomposites: Electrical features and reflection losses

Abstract

Hard/soft (H/S) SrFe 10 O 19 / x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) ( x ≤ 2.5) nanocomposites (NCs) were manufactured using a one-pot citrate sol–gel method. The structural, dielectric, and microwave absorption features of the products were studied using X-ray diffractometry (XRD), scanning/transmission electron microscopy (SEM/TEM), dielectric spectroscopy, and network analysis. The measured XRD powder patterns confirmed the formation of H/S ferrite NCs without impurities. Both SEM and TEM images showed an accumulation of hexagonal and cubic particles. The dielectric and electrical properties of H/S SrFe 10 O 19 /x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) (x ≤ 2.5) NCs were systematically examined for applied voltage frequencies up to 3.0 MHz and measurement temperatures between 20 and 120 °C. The conduction mechanisms related to the dielectric constant, ac/dc conductivity, dissipation factor, and dielectric loss were studied for different compositional ratios. In general, the conductivity variations follows power-law rules with frequencies, largely depending on the compositional ratios of the NCs. The frequency-dependent variation of the dielectric constant in all NCs confirmed the typical dielectric distribution, which is largely dependent on the soft phase content (x). Most of the dielectric parameters of H/S SrFe 10 O 19 /x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) (x ≤ 2.5) NCs can be attributed to grain-to-grain boundaries based on conduction mechanisms, as in most compositional ferrites, which can be clarified using Koop's model. The reflection losses (K ref ) were calculated based on the measured electrodynamic parameters (permeability and permittivity vs. frequency). A nonlinear behavior is observed for K ref with an increase in x. When the soft magnetic phase, Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 , increases from x = 0.0 to x = 2.5, reflection losses decrease from between −17.8 and −20.7 dB to between −0.7 and −9.9 dB, in the 2–10 GHz frequency range. This is attributable to the increasing reflected energy because of the increasing eddy currents, in turn caused by the increasing the electrical conductivity of the NCs.