Investigation of Structural, Elastic, and Optical Properties of Li_0.5Co_0.5FeCrO₄ Spinel for Nonlinear Optical and Optoelectronic Applications

This work presents a detailed investigation of the structural, elastic, and optical properties of Li_0.5Co_0.5FeCrO₄ spinel oxide synthesized via the sol–gel method. Rietveld refinement of x-ray diffraction data confirms the formation of a cubic spinel structure. The structural analysis shows strong agreement between the calculated and refined parameters, supporting the proposed cation distribution. Elastic moduli, including bulk, longitudinal, and shear moduli, were derived from the computed stiffness constants. An increase in lattice parameters and grain size was observed upon the incorporation of Co and Cr ions into the undoped Li_0.5Fe_2.5O₄ sample. Conversely, the observed decrease in Debye temperature (θ_D) suggests that Co and Cr ions enhance lattice vibrations. Ultraviolet–visible (UV–Vis) absorption analysis indicates that Li_0.5Co_0.5FeCrO₄ effectively absorbs light in the UV–Vis range, making it a promising candidate for photovoltaic and photocatalytic applications. The optical bandgap energy of the doped compound (E_g = 1.85 eV) is significantly lower than that of the undoped Li_0.5Fe_2.5O₄ (E_g = 3.41 eV), demonstrating enhanced visible light absorption and improved optoelectronic properties due to Co and Cr incorporation. Additionally, the Urbach energy (E_U = 0.416 eV) suggests a reduction in structural disorder, likely due to increased grain size. Furthermore, theoretical optical parameters such as reflection loss (R_L), polaron radius (R_p), molar refractive index (R_m), molar electronic polarizability (α_m), and nonlinear optical properties highlight the suitability of the synthesized material for optoelectronic applications.