Study on structural, morphological and optical characteristics of spinel chromites: MCr₂O₄ (M= Co, Cu & Ni) synthesized via sol–gel process

The influence of M site substitution on the properties of MCr₂O₄ nanoceramics is examined in this research. This study is an attempt to correlate the structural, morphological and optical properties of M site-modified chromites. The MCr₂O₄ nanoceramics-CuCr₂O₄, CoCr₂O₄ and NiCr₂O₄ were synthesized by a wet-chemical sol–gel auto-combustion method, and were annealed for 4 hours at 900℃. X-ray diffraction investigation revealed that the XRD pattern of CuCr₂O₄ matched with ICSD reference no. 00-034-0424, which confirmed the formation of a tetragonal structure, and the XRD pattern of CoCr₂O₄ and NiCr₂O₄ matched with JCPDS card no. 04-0763 and 89-6615, respectively, which confirmed the single-phase cubic crystal structure with space group Fd-3m. The crystallite sizes calculuated from the Scherrer equation were found to be 9.86nm, 6.73nm and 10.73nm for CuCr₂O₄, CoCr₂O₄ and NiCr₂O_4, respectively. Other parameters, including crystal structure, micro strain, lattice constant, unit cell volume, X-ray density, packing factor, and stacking fault of the calcined powder samples, were determined from data acquired from the X-ray diffractometer. Energy dispersive X-ray spectroscopy (EDX) was employed to confirm the appropriate chromite elements in their expected stoichiometric proportions were free of other impurities. Identification of the functional groups of the samples was performed using Fourier Transform Infrared Spectroscopy (FTIR). The absorption bands characteristic of the tetrahedral and octahedral coordination compounds of the spinel structure were found between 450 and 750cm^-1 for all 3 samples in the spectrum. From the UV-absorption spectra, using Tauc’s plot, the energy bandgap values for CuCr₂O₄, CoCr₂O₄ and NiCr₂O₄ were measured to be 1.66 eV, 1.82 eV and 2.01 eV, respectively. The dielectric properties of the chromites were studied using an LCR meter. Frequency-dependent dielectric properties, including Dielectric constant and Tangent loss, were calculated. These findings suggest the feasibility of the synthesized chromites for optical devices and other optoelectronic applications.