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

Structural and magnetic properties of Al-doped yttrium iron garnet ceramics: Fe-57 internal field NMR and Mossbauer spectroscopy study

The structural and magnetic properties of Al substituted yttrium-iron garnet (Y3AlxFe5-xO12, x = 0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6 and 1.8) ceramic powders synthesized using solution combustion method were investigated. Post combustion, the samples were calcination at 1045 degrees C for 6 h and subsequently at 1200 degrees C for 6 h to obtain phase-pure garnets. X-ray diffraction (XRD) results confirm the formation of garnets with la (3) over bard structure. The occupancy of Y3+ ions in the dodecahedral site and the distribution of Al3+ and Fe3+ ions in the tetrahedral and octahedral sites in the bcc structure of the garnet were confirmed by Rietveld refinement of XRD patterns, Mossbauer spectroscopy and( 57)Fe internal field NMR spectroscopy. For low Al content, Al3+ ions have preference to occupy tetrahedral (T-d) sites than the octahedral (O-h) sites. At higher Al content the distribution of Al tends towards a ratio of 3:2 at the tetrahedral:octahedral site. Increase in Al doping results in the decrease in the lattice parameter due to smaller size of Al-3 + as compared to Fe3+ ion. All the studied samples show coral-network-like surface morphology. The saturation magnetization (M-s) values decrease from -26.94 emu/g to 0.17 emu/g with increase in Al content from 0.0 to 1.8. Further addition of Al makes the sample paramagnetic at RT. Substitution of non-magnetic Al3+ reduces the saturation magnetization rapidly due to the decrease in the superexchange interaction in the crystal. (C) 2018 Elsevier B.V. All rights reserved