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Powder Neutron Diffraction (powder + neutron_diffraction)
Selected AbstractsHigh- and Low-Temperature La2RuO5 by Powder Neutron Diffraction.CHEMINFORM, Issue 51 2005Stefan G. Ebbinghaus Abstract For Abstract see ChemInform Abstract in Full Text. [source] Examination of whewellite kidney stones by scanning electron microscopy and powder neutron diffraction techniquesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2009Michel Daudon Kidney stones made of whewellite, i.e. calcium oxalate monohydrate, exhibit various morphological aspects. The crystalline structure of whewellite at the atomic scale was revisited through a single-crystal neutron study at room temperature using a four-circle automated diffractometer. The possible relationships between the various morphological types of whewellite stones and their structural characteristics were examined at the mesoscopic scale by the use of scanning electron microscopy and at the nanometric scale by powder neutron diffraction. All types of whewellite stones displayed a similar structure at the nanometric scale. However, significant differences were found at the mesoscopic scale. In particular, the crystallites in kidney stones resulting from a genetic hyperoxaluria exhibited a peculiar structure. There was a close relationship between stone morphology and crystallite organization at the mesoscopic level and the effectiveness of extracorporeal shockwave lithotripsy. [source] Octahedral tilting in Pb-based relaxor ferroelectrics at high pressureACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Bernd J. Maier We have employed a combination of powder neutron diffraction and single-crystal synchrotron X-ray diffraction to characterize the pressure-induced phase transitions that occur in the perovskite-type relaxor ferroelectric PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PST-Ba). At ambient pressure the symmetry of the average structure for both compounds is as a result of partial ordering of the Sc and Ta cations on the octahedral sites. At pressures above the phase transition both the neutron and X-ray diffraction patterns exhibit an increase in the intensities of h,k,l = all odd reflections and no appearance of additional Bragg reflections. Synchrotron single-crystal X-ray diffraction data show that the intensity of hhh peaks, h,=,2n,+,1, does not change with pressure. This indicates that the structural distortion arising from the phase transition has a glide-plane pseudo-symmetry along the ,111, cubic directions. Rietveld refinement to the neutron powder data shows that the high-pressure phase has either or symmetry, depending on whether the presence of 1:1 octahedral cation ordering is neglected or taken into account, and comprises octahedral tilts of the type a,a,a, that continuously evolve with pressure. The cubic-to-rhombohedral transition is also marked by a large increase in the anisotropy of the displacement ellipsoids of the Pb cations, indicating larger displacements of Pb cations along the rhombohedral threefold axis rather than within the perpendicular plane. For PST the anisotropy of the Pb displacement parameters decreases at approximately 3,GPa above the phase-transition pressure. For both PST and PST-Ba the average magnitudes of Pb-cation displacements expressed in terms of isotropic displacement ellipsoids gradually decrease over the entire pressure range from ambient to 7.35,GPa. [source] A new layered perovskite, KSrNb2O6F, by powder neutron diffractionACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2007Chung-Yul Yoo The structure of a new layered oxyfluoride, viz. potassium strontium diniobium hexaoxide fluoride, KSrNb2O6F, was refined from powder neutron diffraction data in the orthorhombic space group Immm. The oxyfluoride compound is an n = 2 member of the Dion,Jacobson-type family of general formula A[A,n,1BnX3n+1], which consists of double layered perovskite slabs, [SrNb2O6F],, between which K+ ions are located. Within the perovskite slabs, the NbO5F octahedra are significantly distorted and tilted about the a axis. A bond-valence-sum calculation gives evidence for O/F ordering in KSrNb2O6F, with the F, ions located in the central sites of the corner-sharing NbO5F octahedra along the b axis. All atoms lie on special positions, namely Nb on m, Sr on mmm, K on m2m, F on mm2, and O on sites of symmetry m and m2m. [source] ChemInform Abstract: Magnetic and Crystal Structures of BiCrO3.CHEMINFORM, Issue 34 2010C. Darie Abstract Polycrystalline samples of the title compound are prepared by solid state reaction of Bi2O3 and Cr2O3 (Au capsule, 2 GPa, 805 °C) and characterized by powder neutron diffraction and magnetic susceptibility measurements. [source] | ||||||||||