Structural and Optoelectronic Properties of Mixed Mg–Cu–Cd Spinel Chromites Prepared by the sol–gel Method Under Different Calcination Temperatures

This study investigated the thermal, structural, and optoelectronic properties of Mg_0.4Cu_0.4Cd_0.2Cr₂O₄ spinel chromites prepared by the sol-gel method at different calcination temperatures (850 and 950 °C). According to Rietveld’s refinement of the X-ray patterns, the samples crystallized in the cubic spinel structure (Fd3 ¯ m space group). As the calcination temperature increases, crystallite size and unit cell parameters increase. The FTIR bands of the tetrahedral (A) and octahedral [B] sites shift toward higher wavenumbers with the rise of calcination temperature. From the absorbance and Tauc method, the samples exhibit direct optical transitions. The band-gap energy (E_g) decreases due to the increase in crystallite size. Urbach energies also decrease, implying a decrease in defects and disorders with increasing calcination temperature. In addition, penetration depth, refractive index, extinction coefficient, dielectric constants, conductivity, and loss factor were studied versus wavelength. From these variations in optical parameters, some interesting optoelectronic applications were derived for the as-synthetized Mg_0.4Cu_0.4Cd_0.2Cr₂O₄ samples.