Thanit Tangcharoen

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

In this work, the physical structure, magnetism and local structure of zinc and nickel ferrites (ZnFe2O4 and NiFe2O4) 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 ZnFe2O4 and the ferrimagnetism for NiFe2O4.

Effect of Precursor Concentration on Physical Properties of Cube-Like Zn2SnO4 Powders Synthesized by Co-Precipitation Method

Cube-like Zinc stannate (Zn2SnO4) spinel powders were synthesized by co-precipitation method using chloride starting precursors of zinc and tin. The influence concentration of precursors on relevant physical properties of Zn2SnO4 was investigated by increasing concentration of precursor material at 0.1 to 0.4 M (Zn:Sn at ratio 1:1). Structural properties of as-synthesized and Zn2SnO4 crystal were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray absorption spectroscopy (XAS). The results indicate that as-prepared material without calcination process is in cubic symmetry of zinc hydroxy stannate (ZnSn(OH)6) affirmed by SEM and XRD results. Meanwhile, spinel phase of Zn2SnO4 with strong crystalline and eminent cubic structure can be achieved after calcination at 1000°C. Homogenous dispersion, high crystallinity and good cubic structure of Zn2SnO4 powders are occurred at higher concentration of precursors. Moreover, the oxidation state of these samples were investigated by the Zn K-edge and Sn L3-edge X-ray absorption near edge structure (XANES) using the synchrotron radiation light source. The analyses of XANES spectra revealed that the oxidation state of Zn was +2 and Sn valence was +4 in all Zn2SnO4 samples, which well corresponds to the theoretical values.

Synthesis, Characterization and Multiferroic Properties of Ni0.5Zn0.5Fe2O4-K0.5Na0.5NbO3 Nanocomposites

In this work, nanocrystalline lead-free multiferroic composites of nickel zinc ferrite (Ni0.5Zn0.5Fe2O4) – potassium sodium niobate (K0.5Na0.5NbO3) were synthesized by a sol-gel combustion method. The influence of Ni0.5Zn0.5Fe2O4 content, on the crystal structure, chemical bonding, morphologies, dielectric properties and magnetic behavior of K0.5Na0.5NbO3 was investigated using X-ray diffraction measurement, Raman spectroscopy, scanning electron microscope, LCR meter and vibrating sample magnetometer, respectively. The overall characterization results indicate that the various contents of ferrite and ferroelectric materials in those composites have a significant influence on their multiferroic properties. In addition, this method is proven as one of an ordinary, fast and efficacious way to synthesize functional multiferroic materials with simple availability implements.

Effect of Zn:Al Ratio and Calcination Time on Structural Properties of Zn-Al-O Compound

Zn-Al-O compounds were successfully synthesized via co-precipitation method at pH 8 followed by calcination process at 900 oC. Influence of different precursor (Zn:Al) ratio and calcination period on their structural properties and formation have been investigated. Varying Zn:Al ratio was conducted at 2:1, 1:1, 1:2 and 1:4 with different calcination time at 0, 2, 4, and 6 h. Phase transformation and morphologies were characterized by X-ray diffraction and field-emission scanning electron microscope. Moreover, chemical bonding of Zn-Al-O compound was analyzed by Raman spectroscopy. The results indicated that chemical bonding between Zn-Al oxide evidentially occurred in all samples in composite form and spinel structure. In addition, the amount of Al content considerably contributes to significant aggregation in zinc aluminate (ZnAl2O4) spinel crystalline phase affirmed by XRD result. Meanwhile, SEM images reveal high crystallinity and strong formation of the compound obtained by prolong calcined period.

Synchrotron X-ray absorption spectroscopy study of disordered cation distribution of nanosized zinc ferrite powders

The zinc ferrite (ZnFe2O4) 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.

The disordered cation distribution studies of nanosized zinc ferrite powders by synchrotron X-ray absorption spectroscopy

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.

Sol-gel Combustion Synthesis and Characterizations of Nanocrystalline Zinc, Nickel and Nickel-Zinc Ferrites

In this work, X-ray diffraction (XRD), Raman spectroscopy (RAMAN) and vibrating sample magnetometer (VSM) measurements were employed to investigate the crystal structure, chemical bonding and magnetic properties of the nanocrystalline Zinc, Nickel and Nickel-Zinc ferrites (ZnFe2O4, NiFe2O4 and Ni0.5Zn0.5Fe2O4) which were synthesized by sol-gel combustion method. Moreover, the composition of elements and the electronic structure including the cation distribution for all ferrite samples were examined through synchrotron X-ray fluorescence (XRF) and X-ray absorption near-edge structure (XANES) spectra. The overall characterization results indicate that the different amount of zinc and nickel ions in ferrites has crucial effect on their physical, magnetism and the site occupancy distribution of Fe3+ ions.