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The electronic state and the structural properties of the helical magneto-electric material Cu 2 OSeO 3 is investigated through temperature-dependent synchrotron based x-ray diffraction and x-ray absorption spectroscopy. The x-ray absorption spectra on Cu and Se- K edges indicate that Cu and Se ions are in the 2＋ and 4＋ charge states respectively. The pre-edge corresponding to K -line of Cu in the x-ray absorption spectra cannot be fitted using a single Lorentzian function. At least two different Lorentzian lines are required to fit the pre-edge, which are separated by ∼ 0. 6 ± 0. 042 eV. This separation originates due to the difference in the crystallographic environment of Cu(1) and Cu(2) and the subsequent difference in the energy of the 3 d orbitals of two Cu sites. The obtained energy difference reconfirms the value reported using resonant inelastic x-ray scattering and maximally localized Wannier function calculation. The synchrotron based powder x-ray diffraction indicates significant anomaly in the Cu-O-Cu bond angle around the magnetic transition temperature ( T C ∼ 59 K). Interestingly, the sample show negative thermal expansion in the lattice parameter below T C. Such anomalies can be connected to the exchange-striction mechanism. • Anomalous structural variation in a helical magneto-electric material Cu 2 OSeO 3. • Presence of exchange striction at the magnetic transition. • X-ray absorption spectroscopy indicates ＋2 and ＋4 ionic states of Cu and Se, respectively. • Multiple peak structure of the pre edge of x-ray absorption spectroscopy data corroborating two inequivalent positions of Cu. [ABSTRACT FROM AUTHOR]

Hydrodechlorination reaction of 3-(benzo-1,3-dioxol-5-yl)-3-chloro-2-methylacrylaldehyde in the presence of different low metal content heterogeneous mono- or bimetallic catalysts was tested for the synthesis of the fragrance Helional® (3-[3,4-methylendioxyphenyl]-2-methyl-propionaldehyde). In particular, mono Pd/Al2O3, Rh/Al2O3 or bimetallic Pd-Cu/Al2O3, Rh-Cu/Al2O3 catalysts were tested in different reaction conditions from which it emerged that mono-Rh/Al2O3 was the best performing catalyst, allowing achievement of 100% substrate conversion and 99% selectivity towards Helional® in 24 h at 80 °C, p(H2) 1.0 MPa in the presence of a base. To establish correlations between atomic structure and catalytic activity, catalysts were characterized by Cu, Rh and Pd K-edge XANES, EXAFS analysis. These characterizations allowed verification that the formation of Pd-Cu alloys and the presence of Cu oxide/hydroxide species on the surface of the Al2O3 support are responsible for the very low catalytic efficiency of bimetallic species tested. [ABSTRACT FROM AUTHOR]

Kirkendall effect has played an important role in developing the understanding of atomic diffusion and mass transport in solids. In thin films and multilayers, in which the microstructure may be far from thermal equilibrium, behavior of a system can be very different from that of the bulk. Therefore, there is a great need to understand the peculiarities of Kirkendall shift occurring at nanometer or sub-nanometer length scale in such systems. In the present work, Kirkendall shift in thin films has been measured with sub-nanometer accuracy, by making use of x-ray planar waveguide structures. Using this technique, we report an apparently counterintuitive result of Kirkendall shift associated with self-diffusion in nanocrystalline iron. The cavity of the waveguide consists of two layers of iron having different microstructures, separated by a thin marker layer of Ag. Thermal annealing results in shift of the Ag marker towards the Fe layer having a coarser grain structure. The effect is established unambiguously by studying two samples with the order of the two Fe layers reversed, and a third sample with the two Fe layers having the same microstructure. The result can be understood in terms of the difference in the microstructure of the two Fe layers; difference in the grain size and hence different concentration of the grain boundaries in the two layers results in a net mass transfer from one region to the other. [Display omitted] [ABSTRACT FROM AUTHOR]

Connection between topological surface states (TSS) and large linear magnetoresistance (LMR) is established in tetradymite Bi 2 Te 3 through tuning of native defects. Thorough analysis of temperature dependent synchrotron X-ray diffraction data quantifies 0-D, 1-D and 2-D defect concentrations. Plausible variation of antisite defects is explained via carrier concentration data. Resistivity data divulge contribution of mixed bulk and surface states in the synthesized samples. High Fermi velocity (∼106 ms−1) and low Fermi energy (∼14 meV) of carriers are obtained. Lower defect concentration sample emerges with high magnetoresistance (MR) and higher mobility. Weak antilocalization (WAL) effect, signature of TSS, is revealed from MR. Large (80%), non-saturating LMR along with ultrahigh mobility (∼1 m2V−1s−1) in Bi 2 Te 3 supports the presence of TSS. Magnetoconductance data are fitted with Hikami-Larkin-Nagaoka equation, obtaining further insight on WAL effect. In addition, extracted parameters like disorder correlation length and coherence length explicate the role of defect density on LMR. [ABSTRACT FROM AUTHOR]