A strategy to improve dielectric permittivity of Mg–Zn ferrite by using silver nanoparticles

Abstract

In this work, we used silver nanoparticles (Ag NPs) to enhance the dielectric properties of magnesium-zinc ferrite (Mg–ZnFe2O4) by enhancing local electric field with the creation of nano/micro capacitors between conducting metal particles (Ag NPs) and insulating host (Mg–ZnFe2O4). Mg–ZnFe2O4 was synthesized using the sol-gel method and silver NPs were decorated on magnesium zinc ferrite (Ag@Mg–ZnFe2O4) by employing a sonication approach. The effect of Ag NPs concentration was studied on the structural, morphological, optical, dielectric, and magnetic properties of Ag@Mg–ZnFe2O4 nanocomposite. X-ray diffraction (XRD) confirmed the presence of cubic Mg–ZnFe2O4 and face-centred cubic (FCC) Ag NPs in Ag@Mg–ZnFe2O4 nanocomposite. The structural parameters such as lattice strain, crystallite size and microstrain were correlated with Ag NPs concentration. The morphological study of Ag@Mg–ZnFe2O4 showed uniform decoration of silver at low concentrations; higher concentrations of silver led to reduced covering due to the agglomeration tendency of Ag NPs. Diffused reflectance spectroscopy (DRS) was employed to estimate the effect of Ag NPs on the optical bandgap of Mg–ZnFe2O4. The bandgap narrowing was observed due to the overlapping of the Ag conduction band with the valence band of Mg–ZnFe2O4. All Ag@Mg–ZnFe2O4 samples showed superparamagnetic behaviour and the saturation magnetization was decreased with the increase in the non-magnetic Ag nanoparticles in the nanocomposite. Impedance spectroscopy (IS) was employed to comprehensively analyze the dielectric properties of Ag@Mg–ZnFe2O4. Complex impedance plane plots confirmed the involvement of relaxation phenomena related to grains and grain boundaries in the observed dielectric properties. The decoration of silver nanoparticles was associated with the realization of a high dielectric constant (∼104) in all prepared samples at low frequency. Moreover, uniform decoration of silver was found to show a more stable dielectric constant with relatively low dielectric loss.