Nanocrystalline, homogeneous spinel Ni(1−x)Zn(x)Fe2O4 thin films (where x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) were deposited on glass substrates by using chemical spray pyrolysis (CSP) technique at substrate temperature of (400 ± 10) oC and thickness of about (300 ± 10) nm. Before characterization, all films were annealed in atmosphere ambient at temperature of 520 oC for 4 hours. The structural, morphological and optical properties of these films have been investigated using XRD, AFM, and UV-Visible spectroscopy respectively. The XRD results showed that all films are polycrystalline in nature with cubic structure and preferred orientation along (311) plane according to the (ICDD) card no. 10-0325. The crystallite size calculated by Scherrer’s formula was found to be 14.18 nm for the undoped sample and decreases up to 3.94 nm for the sample with x = 0.10. It is observed also that the lattice constant of Ni–Zn ferrite thin films increases with growing concentration of Zn2+, and this may be attributed to the smaller Ni2+ cations of smaller ionic radii (0.74 Å) being replaced by larger Zn2+ cations of larger ionic radii (0.84 Å). Moreover, the addition of Zn2+ ions causes the migration of Fe3+ ions from tetrahedral sites to octahedral sites. The AFM images show a uniform island-like topography and some structure of clusters could be clearly observed. The size of grains in clusters of the prepared thin films are in the range of several tens of nanometers, which is one order of magnitude higher than the crystallite size calculated from XRD patterns. The optical properties of these films have been studied using UV-Visible spectroscopy. The absorbance and transmittance spectra have been recorded in the wavelength range of (300-900) nm in order to study the optical properties. The optical energy gap for allowed direct electronic transition was calculated using Tauc’s equation and it is found to be 2.96 eV for the undoped Nickel Ferrite thin films. The optical constants including absorption coefficient (α), extinction coefficient (Kₒ), real and imaginary parts of dielectric constant were also calculated as a function of photon energy. In order to investigate the dispersion behavior of the refractive index of the prepared thin films, two terms of Cauchy's equation was applied to the n- λ data and the static refractive index (no) was calculated for all samples.
تاريخ النشر
01/09/2016
الناشر
Journal of Chemical, Biological and Physical Sciences
نبيل علي بكر | Nabeel A. Bakr | 5126