On the structural, refractive index and energy bandgap based optical properties of Lithium ferrite nanoparticles dispersed in silica matrix

Abstract

Lithium ferrite nanoparticles dispersed in silica matrix [Li0.5Fe2.5O4]1–x[SiO2]x (x = 0, 50–90%) have been synthesized using ultrasonic assisted sol–gel method. Agglomeration due to higher surface energy and interparticle interactions is reduced due to dispersion in silica; which modifies the nanoparticle surface and revamp properties of the system. X–ray diffractometer (XRD) measurement reveals simple cubic spinel structure without any impurities. Dynamic magnetic field susceptibility studies show that reversible nature of magnetic domain walls dominates over the irreversible nature. Energy band gap (Eg) determined from UV–Visible (UV–Vis) spectroscopy shows an escalation (1.47 eV to 1.59 eV) for change in silica from 0% to 90%. An empirical formula for refractive index as μ = A(silica content)2+B(silica content)+C has been derived using theoretical fit. With increase in silica content, the refractive index, optical dielectric constant, dielectric susceptibility and oxygen packing density show decrements from 3.82 to 1.77, 8.1204 to 7.6825, 0.6465 to 0.6117 and 70.3157 to 60.974, respectively. The reflectivity, absorption coefficient, molar refractive index, molar electronic polarizability, reflection loss, polaron radius and optical basicity also show reduction. This is attributed to change in density and interparticle interaction due to change in silica content. Dielectric polarizability, transmission coefficient and metallization criterion show increment from 14.85 Å3 to 39.29 Å3, 0.5968 to 0.6086 and 0.2698 to 0.2808; respectively. Observed effects have been ascribed to higher strain, reduction in reflection loss and more non-metallic nature of the samples. Swift changes in parameters indicate their fine tuning through optimum magnitude of silica.