Study of Structural and Optical Properties of Cu–Cr Substituted Mg–Co Spinel Ferrites for Optoelectronic Applications

We have investigated in this work the sintering temperature effects on the structural and optical properties for Mg_0.6Co_0.2Cu_0.2FeCrO₄ spinel ferrites. These samples were prepared using sol–gel method and sintered at two different temperatures (900 °C and 1100 °C). The X-ray diffraction analysis and Rietveld refinement confirm that the sample were well crystallized in the cubic spinel structure (Fd3 ¯ m space group). With increasing sintering temperature, unit cell parameters and crystallites size show an increasing trend. The values of optical band-gap energy were calculated using absorbance, reflectance, and Tauc’s method. These measurements confirm the direct optical transitions for the prepared samples. The band gap energy values decrease due to the increase of crystallites size with increasing sintering temperature. Furthermore, the obtained low Urbach energies confirm the high quality of the prepared samples and imply that the degree of disorder and defects decreases as the sintering temperature rises. The Cauchy parameters were estimated from the variation of the refractive index, and the dispersion energy parameters were evaluated from the Wemple–Didomenico relation. The variations with wavelength of optical constants such as penetration depth, extinction coefficient, conductivity, and dielectric constants have also investigated. The evolution of these parameters reveals the importance of the prepared samples in some interesting optoelectronic applications.