Study of Urbach energy and Kramers–Kronig on Mn and Zn doped NiFe ₂O ₄ ferrite nanopowder for the determination of structural and optical characteristics

Abstract

M _xNi _1-xFe ₂O ₄ spinel ferrite (M = Mn, Zn, and x = 0, 0.05) has been successfully synthesized by co-precipitation technique with hydrazine hydrate reduction agent (instead of NaOH) and Ethylene glycol surfactant. The XRD spectra of the samples illustrated high crystallinity. The structural characterization of pure and doped fcc NiFe ₂O ₄ were calculated by Scherrer, Modified Scherrer, Williamson–Hall, and SSP methods. In comparison of several methods, the Scherrer method is unreasonable method and W–H method has an acceptable range and can calculate both < L > and strain without restriction. The specific surface area in Zn-doped increased, demonstrate increment of adsorption properties in Ni ferrite structure. TEM images revealed the shape of grains is spherical, cubic, and irregular, with a grain size in the range of 35–65 nm. Hysteresis loops illustrated the magnetic behavior of samples. From the reflectance data, the band gap energies were estimated at 1.984, 1.954, and 1.973 eV for un-doped, Mn, and Zn-doped NiFe ₂O ₄ respectively (red shift). The almost low value of Urbach energy for pure, Mn, and Zn -doped NiFe ₂O ₄ indicates low structural disorder, which can approve the high crystallinity of samples. Direct band gap energy (E _g), refractive index, and extinction coefficient were estimated by the Kramers–Kronig method with linear optical evaluations. The E _g by K-K method is in good agreement with the E _g by Kubelka–Munk function.