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

Abstract

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.