Synthesis, crystal structure of the ammonium vanadyl oxalatophosphite and its controlled conversion into catalytic vanadyl phosphates

International audienc

Electronic Structure of EuMo6Se8 Studied by X-Ray Absorption Spectroscopy

[[abstract]]The rare-earth based molybdenum chalcogenides, REMo6Se8 (RE = rare-earth metals) have been extensively studied because of their unique crystal structure based on Mo6Se8 clusters and their outstanding properties involving coexistence of superconductivity and magnetism. Among all these compounds, Ce and Eu based chalcogenides are magnetic and non-superconductors and possess many novel properties. Understanding their electronic structure is likely to provide valuable information about these materials. We employ X-ray absorption near-edge structure (XANES) spectroscopy at Mo and Se K-edges of EuMo6Se8 to identify the local environment respectively around Mo and Se ions and XANES spectra at L3-edge of Eu ion to identify their valence state. Results from this study demonstrate that Se ions in EuMo6Se8 are in two inequivalent sites and the valency of Eu is divalent.[[incitationindex]]SCI[[booktype]]紙本[[countrycodes]]US

Experimental and Theoretical Insights into the Structure of Tellurium Chloride Glasses

International audienceThe structure of the binary chalcohalide glasses TeCl (0.35 ≤ x ≤ 0.65) is considered by combining experimental and theoretical results. The structural network properties are influenced by a competition between ionic and covalent bonding in such glasses. At first, a focus is placed on the detailed information available by using the complementary high-energy X-ray and the neutron diffractions in both the reciprocal and real spaces. The main characteristic suggested by the structure factors S( Q) concerns the presence of three length scales in the intermediate range order. The total correlation function T( r) lets us also suppose that the structure of these glasses is more complicated than Te-chain fragments with terminal Cl as demonstrated in crystalline TeCl. Molecular dynamics simulations were subsequently performed on TeCl and TeCl, and coupled with the experimental data, a highly reticulated network of chalcogen atoms, with a fair amount of chlorine atoms bonded in a bridging mode, is proposed. The simulations clearly lead to a glass description that differs markedly from the simple structural model based on only Te atom chains and terminal Cl atoms. Solid-state NMR experiments and NMR parameters calculations allowed validation of the presence of Te highly coordinated with chlorine in these glasses

Na-23 multiple-quantum MAS NMR of the perovskites NaNbO3 and NaTaO3

The distorted perovskites NaTaO3 and NaNbO3 have been studied using 23Na multiple-quantum (MQ) MAS NMR. NaTaO3 was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO3 were studied. The first, a commercially available sample which was annealed at 900 °C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state

Calculation of the effect of intrinsic point defects and volume swelling in the nuclear magnetic resonance spectra of ZrSiO4.

A variety of computational tools have been used to study the chemical properties of point defects in the crystalline phase of ZrSiO4, and their effect in its lattice parameters. The experimental evidence of a large anisotropic volume swelling in natural and artificially irradiated samples of ZrSiO4 was used to select the subset of defects that give similar lattice swelling for the concentrations studied, namely interstitials of O and Si, and the anti-site ZrSi. Using the relaxed atomic structures, the nuclear magnetic resonance spectra were calculated by means of first principles density functional methods, in order to find additional evidence for the presence of high concentrations of some of these defects in irradiated zircon. The results obtained for the defects singled out before are still compatible with available experimental information. Our calculations also show that volume swelling in crystalline ZrSiO4 would produce a considerable displacement of the 17O and 91Zr chemical shifts towards higher values, whereas the 29Si spectra would be largely independent of the defect-induced swelling

Na~2[(VO)~2(HPO~4)~2C~2O~4].2H~2O: Crystal Structure Determination from Combined Powder Diffraction and Solid-State NMR

Mineral sciences

A solid state highly emissive Cu(i) metallacycle: promotion of cuprophilic interactions at the excited states

International audienc

Extended investigations on Cs2[Mo6Br14]@SiO2 multifunctional nanoparticles: Physico-structural characterizations and toxicity studies

International audienc

Extended investigations on Cs2[Mo6Br14]@SiO2 multifunctional nanoparticles: Physico-structural characterizations and toxicity studies

International audienc