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

The optical and dielectric properties of the ZnFe 2 O 4 –Al 2 O 3 nanocomposite are investigated and compared with the ZnFe 2 O 4 –SiO 2 nanocomposite and ZnFe 2 O 4 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 ZnFe 2 O 4 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 Al 2 O 3 and SiO 2 along with ZnFe 2 O 4 nanoparticles. Transmission electron microscopy observations reveal that ZnFe 2 O 4 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 ZnFe 2 O 4 is 2.89 eV where in presence of alumina matrix the band gap of nanocomposite increases to 2.97 eV. In presence of SiO 2 , a decrease in the band gap of ZnFe 2 O 4 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 ZnFe 2 O 4 –Al 2 O 3 exhibits a significantly enhanced dielectric constant and dielectric loss as compared to that of ZnFe 2 O 4 –SiO 2 as well as ZnFe 2 O 4 nanoparticles. At lower frequencies, the value of dielectric constant is in the order of 10 4 for ZnFe 2 O 4 nanoparticles and in presence of alumina, it enhances to the order of 10 5 . The composite structure exhibits a significantly enhanced ac conductivity with respect to ZnFe 2 O 4 as well as ZnFe 2 O 4 –SiO 2 nanocomposite. The above results suggest that ZnFe 2 O 4 –Al 2 O 3 nanocomposite can be a promising candidate for the development of optoelectronic devices. Highlights ZnFe 2 O 4 –Al 2 O 3 nanocomposite is synthesized by sol–gel auto-combustion method. The structural, optical and dielectric properties ZnFe 2 O 4 –Al 2 O 3 are compared with ZnFe 2 O 4 nanoparticles. ZnFe 2 O 4 –Al 2 O 3 nanocomposite materials have shown the enhancement in the band gap with dramatical decrease in particle size as compared to that of ZnFe 2 O 4 . ZnFe 2 O 4 –Al 2 O 3 nanocomposite shows the superior dielectr