Study of structural, optical, and dielectric properties of sol–gel derived ZnFe₂O₄–Al₂O₃ composite nanoparticles

The optical and dielectric properties of the ZnFe₂O₄–Al₂O₃ nanocomposite are investigated and compared with the ZnFe₂O₄–SiO₂ nanocomposite and ZnFe₂O₄ nanoparticles. The nanocomposite is prepared by simple sol–gel auto-combustion method. The prepared samples are annealed at 800 °C for 6 h. The samples are characterized by infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The formation of single phase cubic spinel structure for ZnFe₂O₄ nanoparticles is confirmed by X-ray diffraction analysis and the average crystallite size is 52.09 nm. In nanocomposite form the reduction in the crystallite size is observed. Studies on infrared spectroscopy confirm the presence of Al₂O₃ and SiO₂ along with ZnFe₂O₄ nanoparticles. Transmission electron microscopy observations reveal that ZnFe₂O₄ nanoparticles are well dispersed in alumina as well as in silica matrix and not highly agglomerated. From UV–visible spectroscopy, the calculated band gap of ZnFe₂O₄ is 2.89 eV where in presence of alumina matrix the band gap of nanocomposite increases to 2.97 eV. In presence of SiO₂, a decrease in the band gap of ZnFe₂O₄ nanoparticles is observed (2.75 eV). Dielectric properties such as dielectric constant, dielectric loss of synthesized nanocomposites are studied as a function of frequency. The dielectric study reveals that ZnFe₂O₄–Al₂O₃ exhibits a significantly enhanced dielectric constant and dielectric loss as compared to that of ZnFe₂O₄–SiO₂ as well as ZnFe₂O₄ nanoparticles. At lower frequencies, the value of dielectric constant is in the order of 10⁴ for ZnFe₂O₄ nanoparticles and in presence of alumina, it enhances to the order of 10⁵. The composite structure exhibits a significantly enhanced ac conductivity with respect to ZnFe₂O₄ as well as ZnFe₂O₄–SiO₂ nanocomposite. The above results suggest that ZnFe₂O₄–Al₂O₃ nanocomposite can be a promising candidate for the development of optoelectronic devices.