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Surface phase diagrams based on density functional theory (DFT) calculations are used to identify stable surface phases present during the oxidation of fuel-cell-relevant organic compounds on Pt-Ru catalysts. The presence of adsorbed CO and O under operando conditions triggers changes in the local structure and composition of the metal alloy’s surface. We find that a Ru-rich Pt-Ru surface stabilizes the mixed CO-O adsorbate phases that we expect to be most conducive to stable and efficient catalyst operation. The predicted surface structures and adsorbate coverages are confirmed by operando X-ray absorption spectra (XAS).

Pre-edge peaks in 3d transition-metal element (Sc, Ti, V, Cr and Mn) K-edge XANES (X-ray absorption near-edge structure) spectra in AO2 (A = Ti and V), A 2O3 (A = Sc, Cr and Mn) and AO (A = Mn) are measured at various temperatures. Quantitative comparisons for the XANES spectra were investigated by using absorption intensity invariant point normalization. The energy position of the difference peak (D peak) is obtained from the difference between the low- and high-temperature XANES spectra. There are two kinds of temperature dependence for pre-edge peak intensity: rutile- and anatase-type. The true temperature dependence of a transition to each orbital is obtained from the difference spectrum. In both anatase and rutile, the pre-edge peak positions of A2 and A3 are clearly different from the D1- and D2-peak positions. The A1 peak-top energies in both phases of VO2 differ from the D1 peak-top energies. The D-peak energy position determined by the difference spectrum should represent one of the true energies for the transition to an independent orbital. The peak-top positions for pre-edge peaks in XANES do not always represent the true energy for independent transitions to orbitals because several orbital transitions overlap with similar energies. This work suggests that deformation vibration (bending mode) is effective in determining the temperature dependence for the D-peak intensity.

Pre-edge peaks in 3d transition-metal element (Sc, Ti, V, Cr and Mn) K-edge XANES (X-ray absorption near-edge structure) spectra in AO

The thermal diffusivity, κ , and conductivity, λ , of Ca-doped stabilized zirconia were simultaneously measured up to 5.3 GPa and 700 K employing the pulse transient method. From κ and λ , heat capacity, C , was also derived. The temperature dependences of κ and λ at 5.3 GPa were found to be very small, and may be due to oxygen ion conduction. The present data are especially useful for designing a high-pressure cell in a Kawai-type apparatus, where Ca-doped stabilized zirconia has been frequently used as thermal insulator around a heater.

XANES (X-ray absorption near-edge structure) spectra of the TiK-edges ofATiO3(A= Ca and Sr),A2TiO4(A= Mg and Fe), TiO2rutile and TiO2anatase were measured in the temperature range 20–900 K. Ti atoms for all samples were located in TiO6octahedral sites. The absorption intensity invariant point (AIIP) was found to be between the pre-edge and post-edge. After the AIIP, amplitudes damped due to Debye–Waller factor effects with temperature. Amplitudes in the pre-edge region increased with temperature normally by thermal vibration. Use of the AIIP peak intensity as a standard point enables a quantitative comparison of the intensity of the pre-edge peaks in various titanium compounds over a wide temperature range.

Zr and Ti K-edge XANES spectra of PbZrO3, PbTiO3 and BaTiO3 perovskite-type compounds were measured in the temperature range from 10K to 850K. Quantitative comparisons for the near-edge spectra were performed in a wide temperature range using the absorption intensity invariant point (AIIP) standardization. Clear temperature dependence for pre-edge shoulder is identified by the calculating the temperature difference of the XANES spectrum intensity. Decrease of pre-edge shoulder and peak intensity is observed only in the para- and ferro-electric phases and draw curves, not straight lines. The gradients for shoulder and pre-edge peak intensity are rich in a variety. The decrease in absorption of pre-edge peak and shoulder is speculated due to the shift from the off-centre position of the Zr atom with respect to the oxygen octahedron to center position. The Zr ion in the PbZrO3 para-electric phase has same temperature behaviors of Ti ions in the ferroelectric perovskite.

The local structures of meteorite fusion crusts were studied by Ca, Ti and Fe K-edge XANES and EXAFS spectroscopy. The surface of meteorites were melted and volatilized with extreme high temperature and large temperature gradient when meteorites were rushed into atmosphere. This study indicated that meteorite fusion crusts have unique local structures. The local structures of fusion crusts differ from tektites especially in intensity of the shoulder in the rising flank of the edge in Ca XANES spectra. It is consistent with chemical composition change by the volatilization of Si at fusion during atmospheric entry. The high estimated Fe3+/ (Fe2++Fe3+) ratio in meteorite fusion crusts indicates that meteorite fusion crusts are formed into atmospheric oxidation condition. The Ca-O distances in meteorite fusion crusts are 2.612.66 A and are extremely longer than in other natural glasses. The fusion crusts have unique local structure since they experienced extremely high temperature and short quenching time. The XAFS method is effective in distinction of meteorite fusion crusts and classification of natural glass.

XANES (X-ray absorption near-edge structure) spectra of the Ti K-edges of ATiO3 (A = Ca and Sr), A2TiO4 (A = Mg and Fe), TiO2 rutile and TiO2 anatase were measured in the temperature range 20-900 K. Ti atoms for all samples were located in TiO6 octahedral sites. The absorption intensity invariant point (AIIP) was found to be between the pre-edge and post-edge. After the AIIP, amplitudes damped due to Debye-Waller factor effects with temperature. Amplitudes in the pre-edge region increased with temperature normally by thermal vibration. Use of the AIIP peak intensity as a standard point enables a quantitative comparison of the intensity of the pre-edge peaks in various titanium compounds over a wide temperature range.

A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3perovskite has been performed over the temperature range 298–778 K. A transition from a tetragonal (P4mm) to a cubic (Pm \overline 3 m) phase has been revealed near 413 K. In the non-centrosymmetricP4mmsymmetry group, both Ti and O atoms are displaced along thec-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti4+and Ba2+cations occupy off-center positions in the TiO6and BaO12polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions.

The local structures of tektites and natural glasses were studied by Zr K-edge XANES and EXAFS in order to provide quantitative data on bonding distances and coordination numbers. The XAFS measurements were performed at the beam line BL-NW10A of the PF-AR in National Laboratory for High Energy Physics (KEK), Tsukuba, Japan. Zr4+ ion in tektite has different kinds of coordination environment. Various natural glasses are formed under different physical conditions. Impact-related glass, fulgurite and volcanic glasses are typical natural glasses. Upon a devastating impact of a giant meteoroid on the Earth, particles of the Earth's surface were melted and catapulted into outer space, where they finally solidified and fell back to the Earth. Tektites should be formed by this series of processes [1]. Tektite has special local structure of Ca[2]. Glass structure is affected by the pressure and temperature conditions during the glass formation and quenching process. This study indicated that different formation process of natural glasses gives different local structure of zirconium ions. The Zr K-edge XANES spectra of tektite have the double post-edge peaks with different heights. The volcanic glasses and other impact-related glasses such as impactite possessed more simple XANES patterns. The average coordination number of Zr4+ in darwin glass, LDG, volcanic glass and tektite are between 6 and 7. The eight-coordinated Zr4+ shows different XAFS pattern in suevite and köfelsite. All tektites are classified in same type. According to EXAFS measurements, Zr-O distances in tektites are 2.198 – 2.215Å and XANES spectra of tektites have similar shape. It indicates that tektites have similar Zr local structure with 7-fold coordination Zr ions. Impact-related glasses are classified to different types. Volcanic glasses are classified to same types. Impact glasses are formed under different geological processes at impact event and are experienced different physical environments.