Papers by Keyword: X-Ray Absorption Spectroscopy

Abstract: Sapphire, an inorganic gem-material in a variety of corundum, mainly consists of alpha-alumina (α-Al₂O₃) structure. The geological origins of sapphire are related to either basaltic or metamorphic rocks. The causes of the color on sapphire are some trace elements such as Cr, Fe, and Ti. It could be mentioned that Ti atoms have cooperated with Fe atoms for creating the blue color. In this study, X-ray absorption spectroscopy (XAS) technique focused on the x-ray absorption near edge structure (XANES) and the extended x-ray absorption fine structure (EXAFS) is employed to identify the oxidation state of Ti atoms and Ti-O bond length on sapphire samples. The Ti K-edge XANES and EXAFS spectra of natural sapphires were carried out using the 13-channel array germanium detector in fluorescence mode. The XANES spectra showed that the oxidation state of Ti was Ti⁴⁺ regardless of Fe content. Moreover, the Ti-O bond length on a-Al₂O₃ was equal to the Ti-O bond length on rutile (TiO₂) analyzed from the EXAFS spectra. From these results, it could be concluded that the oxidation state of Ti atoms on natural sapphires was Ti⁴⁺ which substitutes Al³⁺ on the sapphire structure.

Abstract: The red color of ruby is caused by Cr³⁺ impurities substituting Al³⁺ in Al₂O₃ structure. The complete substitution of Al³⁺ by Cr³⁺ produces Cr₂O₃ that has the green color. In this study, we focused on the phase transition of solid solution between corundum (Al₂O₃) and eskolaite (Cr₂O₃) mineral series. A series of Al₂O₃-Cr₂O₃ samples were prepared by mixing fine powder of Al₂O₃ and Cr₂O₃ in various ratios. They were ground together and then recrystallized. The obtained crystals were ground again in powder form for X-ray absorption near edge structure (XANES) measurements to avoid polarization dependence. The measurements were carried out at the Cr K-edge absorption energy using a 13-channel array Ge detector in the fluorescence mode. The XANES spectra showed line-shape transitions for 0.125 to 100% variation of Cr₂O₃. Significant variations in transitions were found when the Cr₂O₃ content was between 20% and 80%. With Cr₂O₃ concentration increasing, the sample colors apparently turned from pink to dark green. CIELAB color index measurements were performed. The variations of line-shape spectra of the Al₂O₃-Cr₂O₃ samples were found to be consistent with the CIELAB color index results. This Cr K-edge XANES study could be useful for the research in mineral sciences.

Abstract: High Strength Low Alloy (HSLA) steels or microalloyed steels are developed in order toimprove the strength and toughness compared with conventional carbon steels. During the reheatingprocess at 1250-1300 °C for a few hours, the furnace consumes large amount of energy, and the slabsuffers from thick oxide scale. This results in significant mass loss. The long reheating time ensuresmaximum dissolution of the microalloying elements, which must be kept to precipitate duringcooling at the end of the hot rolling process. To minimise the reheating time and save the energyconsumption, this research studied the dissolution kinetics of vanadium in HSLA steel. Vanadium isa main microalloying element added to provide higher strength mainly by precipitation hardening. Itis supposed to be dissolved readily according to the solubility limit. The samples were reheated to1200 °C and 1250 °C for 0, 10, 30, and 60 s. After that the fraction of vanadium dissolved in the solidsolution and the remaining undissolved phases of VC, CN, and V(C,N) were measured bysynchrotron XAS. As soon as the sample reaches as low temperature as 1200 °C, a large atomicfraction of 0.878 of vanadium can be dissolved in the solid solution.

Abstract: This work is aimed at synthesizing lead zinc niobate powders which consist of pyrochlore phases by modified solid-state reaction via a rapid vibro-milling in difference three synthesis routes: mixed oxide precursor (PZN-M) , columbite precuresor (PZN-C) and lead niobate precuresor (PZN-P). It involves the fabrication of PZN powder and study of phase formation and local structural environment of Zn ions by using X-ray Diffraction (XRD) and X-Ray Absorption Spectroscopy (XAS) techniques that compared the amount of pyrochlore phases with perovskite phase.

Abstract: ZnO semiconductor doped with a few per cent of some transition metal ions can exhibit above room temperature ferromagnetism, transforming it into a very promising candidate for future spin-electronic applications. In the present article we have compared the electronic structure of two polycrystalline ZnMnO pellets doped with diluted Mn concentration (2% and 4%), carefully characterized by SQUID and XRD, including Rietveld refinement. The characterization measurements established that the samples have the ZnO lattice with ZnS type Wurtzite hexagonal symmetry and no detectable impurities. The samples exhibit distinctly different magnetic properties. The 2% sample displayed a clear FM ordering at 300 K while the 4% sample did not show any ordering down to 5K. The electronic structure of these two samples has been investigated using Mn L23 x-ray absorption spectroscopy, Zn 2p and 3p, Mn 3p and O 1s x-ray photoemission spectroscopy. Our aim was to find out how the changes in the electronic structure can correlate to the observed magnetic properties in such diluted magnetic semiconductor materials. The results show that most of the Mn ions of the ferromagnetic sample are in the divalent state. For the higher Mn percent nonmagnetic sample, a larger contribution of higher oxidation Mn states are dominant and the oxygen content also increases. The two factors can be correlated to the suppressed ferromagnetism, though it is hard to pinpoint that which of these two weighs more in the suppression mechanism.

Abstract: Iron phthalocyanine (FePc) thin films prepared by thermally evaporated from as received and purified powders were studied. The molecular interaction between FePc thin films and acetone vapor was studies by X-ray photoemission spectroscopy (XPS) and optical absorption spectrometer. The core level XPS spectra and optical absorption spectra showed slightly different between the spectra before and after acetone exposure. For FePc film evaporated with purified powder, only the Fe 2p3/2 spectra at about 712 eV appeared and the height of peak dramatically decreased. Iron K-edge X-ray absorption near edge structure (XANES) spectra was used to investigate iron atom in as received and purified powders and also study the interaction between FePc molecule and methanol vapor. The X-ray diffraction pattern of as received, annealed and purified FePc powder were investigated to study the crystal reformation and Raman spectroscopy was used to investigate iron atom vibration in as received FePc film.

Abstract: In this work, an experimental X-ray Absorption Spectroscopy (XAS) measurement was employed to determine the local structure of Mn in BaTiO3. Synchrotron X-ray absorption near-edge structure (XANES) experiments were performed on Mn-doped BaTiO3 samples. The BaTi0.8Mn0.2O3 powders were used for the XAS experiment. XAS spectra at the Mn K-edge were recorded in transmission mode. The spectra were collected at ambient temperature with a Ge(111) double crystal monochromator and recorded after performing an energy calibration. The features of the measured Mn K-edge XANES were consistent with Mn on the Ti site and inconsistent with Mn on other sites. The clear agreement was the strongest evidence of Mn substituting for Ti in BaTiO3.

Abstract: Barium titanate, BaTiO3 is a significant material for electronic components. It was known that Sr2+ substitution on Ba ion can strongly modify ferroelectric properties of BaTiO3 but the structural change has not been fully understood. An X-ray absorption spectroscopy at the Ti K-edge (4966 eV) and the Ba LIII-edge (5247 eV) was employed to investigate the structure of Ba1-xSrxTiO3 (BSTO) with 0

157