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The disordered cation distribution studies of nanosized zinc ferrite powders by synchrotron X-ray absorption spectroscopy
(2016-04-26)
Tangcharoen, Thanit
;
Klysubun, Wantana
;
Kongmark, Chanapa
;
Pecharapa, Wisanu
The non-equilibrium site occupancy of zinc (Zn2+) and ferric (Fe3+) ions in dissimilar nanosized zinc ferrites (ZnFe2O4)powders obtained from the different milling time (0 to 24 h) of the as-combusted powders was investigated through Zn and Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. Compared with the bulk specimen of zinc ferrite, both XANES and EXAFS spectra of nanosized zinc ferrite powders clearly exhibit the large Zn2+ ions translocation from the tetrahedral (A) sites to the octahedral (B) sites leading to the movement of many Fe3+ ions in the opposite direction without the variation in the long-range structural order.
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Synchrotron X-ray absorption spectroscopy study of disordered cation distribution of nanosized zinc ferrite powders
(2016-01-01)
Tangcharoen, Thanit
;
Kongmark, Chanapa
;
Klysubun, Wantana
;
Pecharapa, Wisanu
The zinc ferrite (ZnFe<inf>2</inf>O<inf>4</inf>) powders of various nanoparticle sizes were synthesised at different milling times (0 to 24 h) of the as-combusted powders. The non-equilibrium site occupancy of zinc (Zn2+) and ferric (Fe3+) ions was investigated through Zn and Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. The XRD and SEM strongly confirm the particle size of these ferrites decreasing with the increasing milling time. Compared with the bulk specimen of zinc ferrite, both XANES and EXAFS spectra of zinc ferrite powders clearly exhibit the large translocation of Zn2+ ions from the tetrahedral (A) sites to the octahedral (B) sites and the opposite translocation of some of Fe3+ ions without affecting the long-range structural order. Moreover, the curve-fitting analysis of Zn and Fe K-edge EXAFS spectra indicates that the degree of inversion increases as the particle size decreases resulting in significant differences in the magnetic behaviours.
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Synchrotron X-ray absorption spectroscopy study of the local atomic structures and cation ordering in perovskite- and spinel-type zinc stannate synthesized by co-precipitation method
(2015-12-15)
Tangcharoen, Thanit
;
Kongmark, Chanapa
;
Pecharapa, Wisanu
Zinc stannate nanocrystalline powders with two different crystal structures were synthesized from two different initial Zn2+/Sn4+ ratios by a simple co-precipitation method. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) techniques were used to investigate crystal structure, oxidation, and cation ordering of the after-calcined powders. XRD patterns clearly showed that the ZnSnO<inf>3</inf> perovskite phase was obtained using an equal initial Zn2+/Sn4+ ratio of 1:1, while a double Zn2+ excess sample (2:1) produced the pure Zn<inf>2</inf>SnO<inf>4</inf> spinel phase. The chemical shifts in Zn K- and Sn L3-edge XANES spectra supported that only Zn2+ and Sn4+ ions existed in these stannate samples. Moreover, the theoretical simulation of the Zn K-edge EXAFS experimental data also indicated a change in the cation ordering from orthorhombic, for perovskite ZnSnO<inf>3</inf>, to cubic for spinel Zn<inf>2</inf>SnO<inf>4</inf>. This is the first time that the local atomic structural characterization of zinc stannate powders derived from EXAFS analysis has been presented.
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A comparison of cation distribution and valence state in spinel crystal structure of zinc and nickel ferrites using the synchrotron X-ray absorption spectroscopy (XAS) analysis
(2014-07-24)
Tangcharoen, Thanit
;
Klysubun, Wantana
;
Ruangphanit, Anucha
;
Pecharapa, Wisanu
In this work, the physical structure, magnetism and local structure of zinc and nickel ferrites (ZnFe<inf>2</inf>O<inf>4</inf> and NiFe<inf>2</inf>O <inf>4</inf>) synthesized by typical sol-gel combustion method, were investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The formation of the single phase cubic spinel crystal structure and the different values of crystallite size (D), interplanar distance (d) and lattice constant (a) for all ferrite samples were evaluated by the XRD data. The VSM measurement provides the characteristic magnetic hysteresis loop (M-H) for each sample which was found to be significantly different from each other. The chemical shifts in Zn, Ni and Fe K-edges XANES spectra indicate the existence of Zn2+, Ni2+ and Fe3+ ions in these ferrites. The EXAFS spectra analyses applied to track Zn, Ni and Fe cation distribution indicate the distinct character of spinel crystal structure of both ferrites. The results exhibit that zinc ferrite is a normal spinel, while the nickel ferrite is an inverse spinel. Moreover, these EXAFS spectra analyses reveal that the distances between metal ion (Zn2+ or Ni2+) to central oxygen ion and to Fe3+ ions in the opposite lattice site for each ferrite sample are unequal which highly affect its magnetism. The overall simulated results are one of the important evidence encouraging the explanation on the paramagnetism for ZnFe<inf>2</inf>O<inf>4</inf> and the ferrimagnetism for NiFe<inf>2</inf>O<inf>4</inf>. © 2014 Taylor & Francis Group, LLC.
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Synchrotron X-ray absorption spectroscopy and magnetic characteristics studies of metal ferrites (metal = Ni, Mn, Cu) synthesized by sol-gel auto-combustion method
(2014-01-01)
Tangcharoen, Thanit
;
Klysubun, Wantana
;
Kongmark, Chanapa
;
Pecharapa, Wisanu
In this work, the metal ferrites MFe<inf>2</inf>O<inf>4</inf> (M = Ni, Mn, Cu) were synthesized from metal nitrate precursors by the sol-gel auto-combustion method using diethanolamine (DEA) as a potential fuel. The crystal structures of these ferrite powders were characterized by X-ray diffraction (XRD) technique confirming the complete formation of the single-phase cubic spinel crystal structure. The ferrimagnetism characteristic and the difference of the magnetic properties such as saturation magnetization (M<inf>s</inf>), remanent magnetization (M<inf>r</inf>), and coercivity (H <inf>c</inf>) for each after-calcined ferrite sample were scrutinized through the ferrimagnetic hysteresis loop (M-H) obtained from the vibrating sample magnetometer (VSM) measurement. Moreover, the cation distribution and valence state of these ferrites were investigated by the Ni, Mn, Cu, and Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra using the synchrotron radiation light source. From the XAS results, the analyses of both XANES and EXAFS spectra show the existence of accurate oxidation state for transition metal ions and the interionic distance to the nearest neighbors in the spinel crystal structure. In particular, the curve-fitting analysis of Ni, Mn, Cu, and Fe K-edge EXAFS spectra indicates that the degree of inversion in these metal ferrites is entirely different and found to be 0.2 for MnFe<inf>2</inf>O<inf>4</inf>, 0.8 for CuFe<inf>2</inf>O <inf>4</inf>, and 1.0 for NiFe<inf>2</inf>O<inf>4</inf>, which are the important information for understanding their effects on relevant magnetic properties. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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