Tunable Optical Bandgap of Gadolinium Substituted Nickel-Zinc Ferrite Nanoparticles-Effect of Calcination Temperature on Its Optical Parameters

The gadolinium substituted nickel-zinc ferrite nanoparticles of the composition, Ni0.5Zn0.5Gd0.05Fe1.95O4 were prepared using sol-gel method. In order to study the effect of calcination temperature on the optical parameters, the prepared powder was divided into five parts. The first part was taken as the as-prepared sample and the remaining four parts were calcinated at different temperatures, 600°C, 700°C, 800°C & 900°C. The X-ray diffraction patterns revealed the formation of cubic spinel structure with single phase and Fd3m space group. The crystallite size was increased from 11.75 nm to 18.13 nm as the calcination temperature increased from 600 to 900°C whereas as-prepared sample exhibited 17.61 nm. The dislocation density was decreased from 7.243 × 10-3 to 3.042 × 10-3 nm-2 as the calcination temperature increased from 600°C to 900°C. The micro strain was decreased from 10 × 10-4 to 6.452 × 10-4 as the calcination temperature increased from 600°C to 900°C. The characteristic absorbance peaks were obtained at 255.2 nm for the ferrite nanoparticles of as-prepared and calcinated at 600°C and 800°C whereas it was obtained as 252.8 nm for the sample calcinated at 700°C and there was no such characteristic peak in UV-visible range for the sample calcinated at 900°C; it is expected in the below 200 nm region. The optical energy gap was calculated using Kubelka-Munk equation based on Tauc’s plot and found in the range 4.100 eV to 5.389 eV. The lowest energy gap of 4.100 eV exhibited by the sample calcinated at 700°C and the highest energy gap of 5.389 eV by the sample calcinated at 900°C. It is concluded that the tunable band gaps can be obtained with varying calcination temperature.