The Influence of Calcination Temperature on Structural, Optical, and Impedance Spectroscopy Properties of Mixed Ni0.4Cd0.3Co0.3Fe2O4 Spinel Ferrites Synthesized Using the Sol–Gel Method

In this study, the impact of varying calcination temperatures on the structural, impedance spectroscopy, and optical properties of Ni 0.4 Cd 0.3 Co 0.3 Fe 2 O 4 spinel ferrites was examined. The experimental XRD results indicated that increasing the calcination temperature resulted in an increase in both grain size and cell parameters. The samples display direct optical transitions based on the Tauc method. With increasing grain size, band-gap energy ( E g ) and activation energy ( E a ) decrease. Increased calcination temperature also reduces Urbach energy ( E u ) due to the decrease in defects and disorder in the samples. Besides, optical dielectric constants, conductivity, penetration depth, loss factor, refractive index and extinction coefficient are also studied. The Nyquist diagram modeling revealed that the conduction mechanism in the samples is influenced by both grain and grain-boundary contributions. To explain the conduction process, the Overlapping-Large Polaron Tunneling model (OLPT) was employed. Additionally, the materials exhibited high electrical resistivity and low dielectric constants and losses at higher frequencies. These properties make the Ni 0.4 Cd 0.3 Co 0.3 Fe 2 O 4 samples well-suited for applications involving high-frequency and microwave absorption.