Physical properties of Cd0.3Ni0.2Co0.3Cu0.2Fe2O4 spinel ferrites under different calcination temperatures

In this study, we examined the effect of calcination temperature on the structural, electrical transport and optical characteristics of Cd0.3Ni0.2Co0.3Cu0.2Fe2O4 spinel ferrites. The samples, designated as S850 and S950, were prepared using sol-gel method, followed by calcination at 850 degrees C and 950 degrees C, respectively. The structural analysis for the samples S850 and S950 reveals its crystallization in the cubic spinel structure (Fd3m spacegroup). Subsequently, as the temperature of calcination increased there was an increasing trend observed in both the unit cell parameters and average crystallite size. In addition, we studied the optical properties of the samples. Using Tauc" s reflectance method, the optical band gap energy values (E-g) were estimated. These analyses confirmed the direct optical transitions of the samples. Furthermore, the direct band-gap energies for S850 and S950 were found as E-gd = 1.875 eV and E-gd = 1.746 eV, respectively. Then, the calculated low Urbach energies (E-u = 1.05 eV for S850 and E-u = 1.01 eV for S950) revealed the high quality of our samples. This observation implies that increasing the calcination temperature reduces the level of disorder and defects. The study also investigated the changes in optical constants, like the extinction coefficient and penetration depth, as a function of wavelength. The refractive index changes were used to determine the Cauchy parameters, while the Wemple-Didomenico equation was utilized to estimate the energy parameters related to dispersion. The research also focused on analyzing the optical dielectric and optical conductivity constants. Increased calcination temperature also decreases band-gap energy (E-g) and activation energy (E-a). Equivalent circuit modeling of Nyquist plots indicates that both grain and grain boundary contributions influence the conduction mechanism in the specimens. The Overlapping-Large Polaron Tunneling (OLPT) model was employed to elucidate the conduction mechanism observed in the specimens. Moreover, when subjected to high frequencies, the synthesized materials demonstrate reduced dielectric constants and minimal dielectric losses. Additionally, they exhibit heightened electrical resistivity under these conditions. These features make the Cd0.3Ni0.2Co0.3Cu0.2Fe2O4 materials a potential choice for applications that require absorption of microwaves and high-frequency signals.