The impact of sintering temperature on structural properties, optical and dielectric parameters under photon energy of Ni_0.6Cd_0.4FeAl_0.5Cu_0.5O₄ for optoelectronic devices

The impact of calcination temperature on the structural and optical properties of Ni_0.6Cd_0.4FeAl_0.5Cu_0.5O₄ spinel ferrites was investigated in this work. These samples were prepared using sol-gel method and sintered at two different temperatures (950 °C and 850 °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 direct bandgap energy calculated, respectively for S950 and S850 are E_gTau = 2.6 eV, E_gTau = 2.41 eV, E_gDRS = 2.41 eV and 2.39, E_{gdrivAbso =} 2.45 eV and 2.47 eV and E_gdrivRefel = 2.382 eV and 2.377 eV. This shift of E_g value between Tauc method, spectra diffuse reflectance spectroscopy (DRS) is related to the lack of precision of Tauc method. 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 determined from the variation of the refractive index. In the other hand, 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 low dielectric value and the relatively small bandgap energy show that this compound can be proposed as a good candidate for optical and optoelectronic applications.