Determination of the response of pentaerythritol tetranitrate to static high pressure up to 4.2 GPa by neutron diffraction

Neutron powder diffraction experiments were performed on pentaerythritol tetranitrate explosive up to 4.28 GPa. For deuterated samples the changes in lattice parameters, intramolecular torsional angles and molecular rotation were measured. The lattice parameter changes were different from those observed in protonated samples. However, there is no evidence of a phase transition or change in molecular symmetry

A comparative study of experimental configurations in synchrotron pair distribution function

The identification and quantification of amorphous components and nanocrystalline phases with very small crystal sizes, smaller than ~3 nm, within samples containing crystalline phases is very challenging. However, this is important as there are several types of systems that contain these matrices: building materials, glass-ceramics, some alloys, etc. The total scattering synchrotron pair distribution function (PDF) can be used to characterize the local atomic order of the nanocrystalline components and to carry out quantitative analyses in complex mixtures. Although the resolution in momentum transfer space has been widely discussed, the resolution in the interatomic distance space has not been discussed to the best of our knowledge. Here, we report synchrotron PDF data collected at three beamlines in different experimental configurations and X-ray detectors. We not only discuss the effect of the resolution in Q-space, Qmax ins of the recorded data and Qmax of the processed data, but we also discuss the resolution in the interatomic distance (real) space. A thorough study of single-phase crystalline nickel used as standard was carried out. Then, selected cement-related samples including anhydrous tricalcium and dicalcium silicates, and pastes derived from the hydration of tricalcium silicate and ye’elimite with bassanite were analyzed.This work is part of the PhD of Mr. Jesus D. Zea-Garcia. This work was supported by Spanish MINECO and FEDER [BIA2017-82391-R research project and I3 [IEDI-2016-0079] program]

Determination and mitigation of the uncertainty of neutron diffraction measurements of residual strain in large-grained polycrystalline material

For large-grained samples it is advantageous to perform pairs of neutron diffraction measurements at the same spatial location but rotated 180° around the geometric centre of the gauge volume as a means of minimizing the scatter coming from the random positioning of grains within the gauge volume

Non-monotonic size dependence of the elastic modulus of nanocrystalline ZnO embedded in a nanocrystalline silver matrix

We present the first high pressure Raman study on nanocrystalline ZnO films with different average crystallite sizes. The problem of low Raman signals from nano sized particles was overcome by forming a nanocomposite of Ag and ZnO nanoparticles. The presence of the nanodispersed Ag particles leads to a substantial surface enhancement of the Raman signal from ZnO. We find that the elastic modulus of nanocrystalline ZnO shows a non-monotonic dependence on the crystallite size. We suggest that the non-monotonicity arises from an interplay between the elastic properties of the individual grains and the intergranular region.Comment: 10 pages, 6 figure

Poly[[μ-(1-ammonio­ethane-1,1-di­yl)bis­(hydrogenphospho­nato)]diaquachloridodisodium]: a powder X-ray diffraction study

The title compound, [Na2(C2H8NO6P2)Cl(H2O)2]n, has a polymeric two-dimensional structure extending parallel to (001). The asymmetric unit contains two Na+ cations located on a centre of symmetry and on a mirror plane, respectively, one half of a bis-phospho­nate anion (the entire anion is completed by mirror symmetry), one chloride anion on a mirror plane and one water mol­ecule in general positions. The two Na+ cations exhibit distorted octa­hedral NaCl2O4 coordination polyhedra, each consisting of two deprotonated O atoms of the bis-phospho­nate anion, of two water mol­ecules and of two chloride anions. Strong O—H⋯O hydrogen bonds between the –OH group and one of the free O atoms of the bis-phospho­nate anion connect adjacent layers along [100], supported by N—H⋯Cl inter­actions. Intra­layer O—H⋯O and N—H⋯O hydrogen bonds are also observed

Visible-light photocatalytic intramolecular cyclopropane ring expansion

Described herein is a new visible-light photocatalytic strategy for the synthesis of enantioenriched dihydrofurans and cyclopentenes by an intramolecular nitro cyclopropane ring expansion reaction. Mechanistic studies and DFT calculations are used to elucidate the key factors in this new ring expansion reaction, and the need for the nitro group on the cyclopropaneThe Spanish Government (CTQ2015-64561-R, CTQ2014-59544-P) and the European Research Council (ERC-CG,contract number:647550) are acknowledge

Experimental evidence for an intermediate phase in the multiferroic YMnO3

We have studied YMnO$_{3}$ by high-temperature synchrotron X-ray powder diffraction, and have carried out differential thermal analysis and dilatometry on a single crystal sample. These experiments show two phase transitions at about 1100K and 1350K, respectively. This demonstrates the existence of an intermediate phase between the room temperature ferroelectric and the high temperature centrosymmetric phase. This study identifies for the first time the different high-temperature phase transitions in YMnO$_{3}$.Comment: 10 pages 5 figures. New version, Additional data, Journal of Physics: Condensed Matter, in Pres