1,721,084 research outputs found
Where zeolites and oxides merge: semi-condensed tetrahedral frameworks
No full textThe synthesis of new inorganic materials constructed with extended lattices has taken place mainly in two areas, complex oxides and porous framework structures. In the former case the drive has been towards controlling electronic and magnetic properties while in the latter domain porosity and the ability to enclathrate small organic or inorganic units has been paramount. Semi-condensed framework materials, whose compositions and structures place them at the borderline of these two classes, are described in this article, such compound types include the sodalite, cancrinite, analcime, zeloites ABW and JBW and scapolite structures. In each case recent chemistry and developments are described particularly with respect to advances made at The University of Southampton. The potential for merging the properties and structures of these two classes of compounds are also discussed
Synthesis and structure of a new family of nickelates: Tl(Ln(2)Sr(2))Ni2O9, Ln = La, Pr, Nd, Sm, Eu, and Cd
No full textA novel series of nickelates described by the formula Tl(Ln(2)Sr(2))Ni2O9, Ln = La, Pr, Nd, Sm, Eu, and Gd, have been synthesized and their structures determined using both powder X-ray diffraction and powder neutron diffraction. The materials are isostructural with the superconducting cuprate, Tl(La2.4Ba1.6) Cu2O9, crystallizing in a tetragonal unit cell, space group I4/mmm, lattice parameters a = 3.8069-3.7667(1) Angstrom and c = 30.055-29.390(1) Angstrom. The compounds adopt the 1201-0201 intergrowth structure, consisting of layers of apex-sharing stoichiometric NiO6 octahedra connected by a Tl0 layer. A decrease in the cell dimensions is observed across the series, consistent with the lanthanide contraction and partial ordering of the strontium and lanthanide ions on the A cationic sites is observed. Magnetic susceptibility data reveal no evidence of long-range magnetic ordering for two of the compounds, TI(La2Sr2)Ni2O9 and Tl(Gd2Sr2)Ni2O9
Propane-1,2-diammonium tetrafluoroberyllate
No full textCocrystallization of the inorganic [BeF4](2-) unit with the organic moiety [NH3CH2CH(NH3)CH3](2+) results in the three-dimensional network of the title compound, (C3H12N2)[BeF4] or C3H12N22+.BeF42-, created by hydrogen bonds between the protonated ammonium groups and the highly electronegative F atoms of the anion. The structure is described in terms of layers related to each other by crystallographic centres of symmetry
Neutron and X-ray powder diffraction studies of the oxynitrides SrW(O,N)(3), Ba3W2(O,N)(8) and Ba3Mo2(O,N)(8)
No full textOxynitrides of composition SrW(O,N)(3), Ba3W2(O,N)(8) and Ba3Mo2(O,N)(8) have been prepared by the ammonolysis of stoichiometric mixtures of oxides and carbonates. Combined Rietveld refinements of powder neutron and powder X-ray diffraction data have allowed the structure of each to be determined. SrW(O,N)(3) was found to have a cubic Perovskite structure whereas Ba3W2(O,N)(8) and Ba3Mo2(O,N)(8) have a layered hexagonal structure. In the hexagonal structures the oxygen and nitrogen atoms are distributed almost randomly over two sites in the unit cell producing 4-fold co-ordination to tungsten and molybdenum, a distorted octahedral co-ordination to one barium site and a 10-fold co-ordination to the other
The effect of calcium on phase formation in the sodium aluminium silicate carbonate system and the structure of NaCaSiO3OH
No full textThe effect of calcium on the hydrothermal syntheses of aluminosilicate frameworks in the presence of carbonate at 150 and 220 degreesC has been studied. Under calcium-free conditions the formation of the cancrinite framework (220 degreesC), [Na-8(CO3)(.)(H2O)(n)][AlSiO4](6)-CAN, and a disordered cancrinite/sodalite intergrowth (150 degreesC) are observed in agreement with the literature. Addition of calcium to the synthesis media,results in its incorporation into these framework structures to give [NaxCay(CO3)({x+2y-6}/2)(H2O)(n)][AlSiO4](6)-CAN, as evidenced by decreases in the cell volumes and EDAX analysis. At high concentrations of calcium a new phase, NaCaSiO3OH, forms and the structure of this material, which contains ordered strongly. hydrogen-bonded SiO3OH units, ha's been defined using neutron diffraction
An analysis of the thermal motion in the negative thermal expansion material Sc-2(WO4)(3) using isotopes in neutron diffraction
No full textA full analysis of thermal motion has been carried out for the negative thermal expansion material Sc-2(WO4)(3) over the temperature range 50-823 K. By obtaining neutron diffraction data from isotopically pure samples of the compositions Sc-2((WO4)-W-184)(3), Sc-2((WO4)-W-186)(3) and natural Sc-2(WO4)(3), coupled With multidata set refinement methods, it is possible to extract anisotropic thermal parameters for individual atoms throughout the temperature range. Results indicate that the thermal motion of two Sc-O-W bridging oxygen atoms with the largest Sc-O-W angles is better represented by thermal toroids consistent with strong local motion of these units. The thermal behavior of the other oxygen atoms in the structures as a function of temperature is normal. Sc-O and W-O bond lengths corrected for the effect of correlated thermal motion show the expected increase with temperature
Crystal structure of the ferromagnetic superconductor RuSr2(Gd1.3Ce0.7)Cu2O10-delta by powder neutron diffraction
No full textThe 1222-type ferromagnetic, superconducting cuprate, RuSr2((Gd1.3Ce0.7)-Gd-160)Cu2O10-delta, contains RuO6 octahedra that are rotated 13.4 degrees around the c-axis and tilted reducing the Cu-O(1)-Ru angle to 168.2 degrees at 295 epsilonK. The oxygen deficiency delta has been determined as 0.22, indicating a hole doping mechanism, similar to that proposed for GdSr2RuCu2O8, facilitates superconductivit
Structure of uranium(VI) oxide dihydrate, UO3. 2H(2)O; synthetic meta-schoepite (UO2)(4)O(OH)(6). 5H(2)O
No full textThe structure of uranium oxide dihydrate, also known as meta-schoepite (UO2)(4)O(OH)(6). 5H(2)O, has been determined from a synthetic single crystal. The structure, at 150 K, space group Pbcn, lattice constants a = 14.6861 (4), b = 13.9799 (3) and c = 16.7063 (5) Angstrom, consists of layers of stoichiometry (UO2)(4)O(OH)(6), formed from edge-sharing UO7 pentagonal bipyramids, interleaved with hydrogen-bonded water molecules. Three of the layer hydroxyl groups are linked through hydrogen bonding to single water molecules and the three remaining OH units form interactions with water molecules that each act as acceptors in two hydrogen bonds. One of the water molecules in the inter-layer region is disordered over two symmetry-related sites and forms hydrogen-bonded interactions only within the layer and with the uranyl O atoms. The relationship of the structure of meta-schoepite to that of schoepite is discussed in detail
Synthesis and structural characterisation of CsCoPO4-ABW
No full textThe cobalt phosphate, CsCoPO4, possessing the zeolite ABW framework topology has been synthesised using a solid state route. Rietveld refinement from powder neutron diffraction data has shown the material to be a direct structural analogue of CsZnPO4 polymorph III. The framework is made up of alternating cobaltate and phosphate tetrahedra sharing vertices with caesium counter cations located in the channels formed. The presence of Co(II) tetrahedra, confirmed by UV visible spectroscopy, is responsible for the intense blue colour of the material. DTA analysis combined with preliminary variable temperature powder X-ray diffraction has shown the presence of a phase transition at approximately 171 degrees C to an orthorhombic unit cell probably isostructural with CsZnPO4 polymorph II
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