1,720,997 research outputs found
New sodalite frameworks; synthetic tugtupite and a beryllosilicate framework with a 3 : 1 Si : Be ratio
No full textCompounds of the formula Na-8[Si(6 + y)BeyAl(6 - 2y)O(24)]X-2, with X = Cl and Br, and y = 1, 2 and 3 have been synthesised and structurally characterised by combined powder X-ray and neutron diffraction profile analysis. These materials adopt the sodalite framework ( SOD) with the tetrahedral species, BeO4, AlO4 and SiO4, disordered across the framework positions. Na-8[Si8Be2Al2O24]Cl-2, (y = 2), is a synthetic analogue of the naturally occurring semi-precious gemstone tugtupite, while Na-8[Si9Be3O24]X-2, X = Cl and Br represents a new tetrahedral framework stoichiometry with a Si : Be ratio of 3 : 1. Additional characterisation using Si-29 MASNMR, IR spectroscopy and high-temperature, neutron diffraction show that the observed structure - property trends found when modelling sodalite materials can be extended to these new framework compositions
Rapid structure determination of the hydrogen-containing compound Cs2C2O4 center dot H2O by joint single-crystal X-ray and powder neutron diffraction
No full textThe structure determination of caesium oxalate monohydrate using single-crystal X-ray diffraction, powder neutron diffraction data and a combination of both has been undertaken. Results show that even for hydrogen-containing materials data collected rapidly on a high-flux neutron diffractometer improve the refinement such that accurate positional and thermal displacement parameters can be extracted for all atom types. This contrasts with structural models extracted from either data set alone that demonstrate the inherent limitations of the individual diffraction methods. The rapidity with which useful neutron diffraction data has been collected from hydrogen-containing compounds, 10 min in this study, indicates that the technique should be widely applicable allowing the facile and accurate extraction of hydrogen positions for many compounds
LnSrScO4 (Ln = La, Ce, Pr, Nd and Sm) systems and structure correlations for A(2)BO(4) (K2NiF4) structure types
No full textThe compounds LnSrScO4, where Ln=La, Ce, Pr, Nd and Sm, have been synthesized. Rietveld profile analysis of powder X-ray diffraction data collected at room temperature reveal that the compounds possess a modified K2NiF4-type structure with orthorhombic cell symmetry formed by tilting of the ScO6 octahedra. Variable temperature (25–1200 °C) powder X-ray diffraction data show that at the highest temperatures the structures of LaSrScO4 and PrSrScO4 transform to the regular tetragonal K2NiF4-structure type but the degree of orthorhombicity (c/a) in the unit cells initially increases on heating for all materials, reaching a maximum near 300 °C. This structural behavior is analyzed in terms of relative ionic radii of the various lanthanides and scandium. A general structural model based on tolerance factors has been developed for the family of materials A2BO4 with various A and B cation sizes
Neutron powder diffraction in materials with incoherent scattering: an illustration of Rietveld refinement quality from nondeuterated gypsum
No full textThe power of the state-of-the-art neutron powder diffractometer suite at the Institut Laue-Langevin for investigating the structure of nondeuterated materials is presented using gypsum, CaSO4·2H2O, as a reference material. It is shown that flexible modern neutron powder diffraction instruments at reactor-based sources can yield data with sufficient counting statistics above the incoherent scattering contribution to perform unconstrained refinements in relatively short time periods (from minutes to a few hours, depending on the sample size and the instrument choice), without the requirement for significant changes to the standard operational modes of the instruments. The results are critically compared with previous literature from single-crystal and powder X-ray and neutron measurements on deuterated and nondeuterated gypsum.<br/
The effect of the cation composition on the synthesis and properties of ultramarine blue
No full textThe effect of potassium cations on the shade of the ultramarine blue pigment system has been investigated through analysis of commercial materials, ion exchange reactions of sodium-form ultramarine blue and a detailed study of the effect of adding potassium sources to ultramarine precursor mixtures. Incorporation of potassium cations has the result of producing redder shade material and the replacement of around 20% of the sodium in the standard reaction mixture produces the optimised red-shade pigment. The origin of this hue control may be a direct effect, involving interaction of potassium ions with the ultramarine blue structure and the S3? chromophore or, more likely, potassium ions aids the stabilisation of S3? within the sodalite framework during the ultramarine blue formation process. In the commercial process, the role of the potassium source in red shade formation may be performed by the incorporation of potassium-rich feldspar additives
Rb2Sb4O11
No full textThe title compound, dirubidium tetraantimonate(V), Rb2Sb4O11, has been synthesized by flux reaction. It is isotypic with known A2Sb4O11 (A = K, Cs) structures and consists of an (Sb4O11)2- skeleton and two Rb atoms as charge-compensating cations. Distorted SbO6 octahedra share edges and corners, resulting in a layered assembly. Alternate stacking of the layers along the c axis leads to the formation of tunnels. The Rb+ ions, surrounded by nine and ten O atoms, respectively, are located in these tunnels. Some atoms in the structure are on special positions of m symmetry (two Sb atoms, both Rb atoms and four O atoms) and 2 symmetry (one O atom
The first organically templated 1D lithioberyllofluoride chain, [LiBe2F7][C4N2H12][H2O]1.5
No full textUsing a combination of hydrothermal and slow evaporation experimental techniques a 1D lithium-beryllium-fluoride chain has been synthesised. In this material a 3D hydrogen bonded network exists between solvent water, a doubly protonated organic piperazinium template and the inorganic chain
Redetermination of CaB<sub>8</sub>O<sub>11</sub>(OH)<sub>4</sub> at low temperature
No full textThe structure of CaB8O11(OH)4 (calcium octaborate tetrahydroxide) [Zayakina & Brovkin ( 1978). Kristallografiya, 23, 1167-1170] has been redetermined at 120 (2) K with improved precision. The O-H ··· O hydrogen-bonding arrangement has been established, based on freely refined H-atom positions
Structure of β-SrRh<sub>2</sub>O<sub>4</sub> from X-ray and neutron powder diffraction
No full textβ-SrRh2O4, a novel high temperature phase, is prepared as black powder by solid state reaction of SrCO3 with Rh in air. The compound crystallises in the space group P63c, Z = 1, with a = 3.0626(2) Å and c = 11.3996(7) Å. The structure consists of CdI2-type layers of edge sharing RhO6 octahedra with an AABB oxygen layer sequence. Strontium is found in partial occupation of both available interlayer sites, in trigonal prismatic coordination.</p
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