Structural, optical and Mossbauer spectroscopic investigations on the environment of Fe in Fe-doped ZnO (Zn1-xFexO) ceramics synthesized by solution combustion method

A series of Fe-doped ZnO (Zn1-xFexO, = 0, 0.01, 0.03, 0.05, 0.07 and 0.10) samples were synthesized by solution combustion synthesis method using metal nitrates as oxidizers and glycine as fuel. A spongy network-type microstructure is observed by the SEM micrographs of all the synthesized samples. For Fe concentration lower than 0.05 (x <= 0.05), formation of phase-pure wurtzite (hexagonal) structured Zn1-xFexO powder with P6(3)mc space group was confirmed from the X-ray diffraction results. However, for x >= 0.07, precipitation of ZnFe2O4 impurity phase was observed. Hence, the solubility limit for Fe in ZnO lattice is about x = 0.05 for the samples synthesized by solution combustion method. Two quadruple doublets observed in the Fe-57-Mossbauer spectra for each of the samples suggest that paramagnetic Fe3+ cations occupy two different lattice sites in the ZnO structure; they are the substitutional sites (1) without distortion of the surrounding structure and (2) with distortion due to the defects present in the surrounding structure. In the DRS spectra, an Urbach-like tail was observed in the band gap region, indicating that Fe-doping in the ZnO lattice modifies the electronic structure and enhances the absorption of visible light. Furthermore, the Kubelka-Munk plots suggest the presence of two different local structures validating the Mossbauer results. We studied the photocatalytic degradation of methylene blue dye using these Fe doped ZnO samples as catalysts and the studies revealed that presence of Fe could lead to the formation of carbonaceous material on the surface of the solution combustion synthesized Zn1-xFexO samples. Overall, our results demonstrate the structural characteristics of Fe in Fe-doped ZnO samples synthesized by solution combustion method