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Neutron Powder Diffraction Data (neutron + powder_diffraction_data)
Selected AbstractsIdentification of single photoswitchable molecules in nanopores of silica xerogels using powder diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5-1 2010Antonio Cervellino Single photoswitchable molecules of (CN3H6)2[Fe(CN)5NO] (GuNP) are embedded into nanopores of an SiO2 xerogel. It is shown that it is possible to identify the structural motif (`fingerprint') of the embedded complex by analyzing neutron powder diffraction data in a limited Q range (Q < 37,nm,1) using the Debye approach. The structural study reveals that the pores are occupied by GuNP monomers with a fill factor of 60,80%. The mutual arrangement of the anion and cations in the GuNP monomer is slightly changed (,1% elongation), while the bond lengths within the anion and cation are changed by less than 0.2% with respect to the single-crystalline form of GuNP. [source] The crystal structure of perdeuterated methanol hemiammoniate (CD3OD·0.5ND3) determined from neutron powder diffraction data at 4.2 and 180,KJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2010A. D. Fortes The crystal structure of perdeuterated methanol hemiammoniate, CD3OD·0.5ND3, has been solved from neutron powder diffraction data collected at 4.2 and 180,K. The structure is orthorhombic, space group Pn21a (Z = 4), with unit-cell dimensions a = 12.70615,(16), b = 8.84589,(9), c = 4.73876,(4),Å, V = 532.623,(8),Å3 [,calc = 1149.57,(2),kg,m,3] at 4.2,K, and a = 12.90413,(16), b = 8.96975,(8), c = 4.79198,(4),Å, V = 554.656,(7),Å3 [,calc = 1103.90,(1),kg,m,3] at 180,K. The crystal structure was determined by ab initio methods from the powder data; atomic coordinates and isotropic displacement parameters were subsequently refined by the Rietveld method to Rp, 2% at both temperatures. The crystal structure comprises a three-dimensionally hydrogen-bonded network in which the ND3 molecules are tetrahedrally coordinated by the hydroxy moieties of the methanol molecule. This connectivity leads to the formation of zigzag chains of ammonia,hydroxy groups extending along the c axis, formed via N,D···O hydrogen bonds; these chains are cross-linked along the a axis through the hydroxy moiety of the second methanol molecule via N,D···O and O,D···O hydrogen bonds. This `bridging' hydroxy group in turn donates an O,D···N hydrogen bond to ammonia in adjacent chains stacked along the b axis. The methyl deuterons in methanol hemiammoniate, unlike those in methanol monoammoniate, do not participate in hydrogen bonding and reveal evidence of orientational disorder at 180,K. The relative volume change on warming from 4.2 to 180,K, ,V/V, is + 4.14%, which is comparable to, but more nearly isotropic (as determined from the relative change in axial lengths, e.g.,a/a) than, that observed in deuterated methanol monohydrate, and very similar to what is observed in methanol monoammoniate. [source] Neutron Powder Diffraction Study of a Phase Transition in La0.68(Ti0.95Al0.05)O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Roushown Ali Crystal structures and structural changes of the compound La0.68(Ti0.95Al0.05)O3 have been studied using neutron powder diffraction data and the Rietveld method in the temperature range from 25° to 592°C. The Rietveld profile-fitting analyses of the neutron data and the synchrotron diffraction profile revealed that the crystal symmetry of the low-temperature phase of La0.68(Ti0.95Al0.05)O3 is orthorhombic Cmmm (2ap× 2ap× 2ap; p: pseudo-cubic perovskite). The unit-cell and structural parameters were successfully refined with the orthorhombic Cmmm for the intensity data measured at 25°, 182°, and 286°C, and with the tetragonal P4/mmm (ap×ap× 2ap) for intensity data obtained at 388° and 592°C. The P4/mmm -to- Cmmm phase transition was found to be induced by tilting of the (TiAl)O6 octahedron. The tilt angle decreased with increasing temperature, reaching 0° at the Cmmm,P4/mmm transition temperature. [source] Revision of the structure of Cs2CuSi5O12 leucite as orthorhombic PbcaACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010A. M. T. Bell The crystal structure of a hydrothermally synthesized leucite analogue Cs2CuSi5O12 has been determined and refined using the Rietveld method from high-resolution synchrotron X-ray and neutron powder diffraction data. This structure is based on the topology and cation-ordering scheme of the Pbca leucite structure of Cs2CdSi5O12, and exhibits five ordered Si sites and one ordered Cu tetrahedrally coordinated (T) site. This structure for Cs2CuSi5O12 is topologically identical to other known leucite structures and is different from that originally proposed by Heinrich & Baerlocher [(1991), Acta Cryst. C47, 237,241] in the tetragonal space group . The crystal structure of a dry-synthesized leucite analogue Cs2CuSi5O12 has also been refined; this has the cubic pollucite structure with disordered T sites. [source] Structures of K0.05Na0.95NbO3 (50,300,K) and K0.30Na0.70NbO3 (100,200,K)ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2009N. Zhang Rietveld refinement using neutron powder diffraction data is reported for the potential lead-free piezoelectric material KxNa1,,,xNbO3 (x = 0.05, x = 0.3) at low temperatures. The structures were determined to be of rhombohedral symmetry, space group R3c, with the tilt system a,a,a, for both compositions. It was found that some of the structural parameters differ significantly in the two structures, and particularly the NbO6 octahedral strains as a function of temperature. The 300,K profile for K0.05Na0.95NbO3 shows the coexistence of rhombohedral and monoclinic phases, which indicates that the phase boundary is close to room temperature; the phase boundary for K0.30Na0.70NbO3 is found to be at approximately 180,K. [source] Structures of 6H perovskites Ba3CaSb2O9 and Ba3SrSb2O9 determined by synchrotron X-ray diffraction, neutron powder diffraction and ab initio calculationsACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2008Budwy Rowda The structures of the 6H perovskites Ba3B2+Sb5+2O9, B = Ca and Sr, have been solved and refined using synchrotron X-ray and neutron powder diffraction data. Ba3CaSb2O9 and Ba3SrSb2O9 have monoclinic C2/c and triclinic space-group symmetries, respectively, while Ba3MgSb2O9 has ideal hexagonal P63/mmc space-group symmetry. The symmetry-lowering distortions are a consequence of internal `chemical pressure' owing to the increasing effective ionic radius of the alkaline-earth cation in the perovskite B site from Mg2+ (0.72,Å) to Ca2+ (1.00,Å) to Sr2+ (1.18,Å). Increasing the effective ionic radius further to Ba2+ (1.35,Å) leads to decomposition at room temperature. The driving force behind the transition from P63/mmc to C2/c is the need to alleviate underbonding of Ba2+ cations in the perovskite A site via octahedral rotations, while the transition from C2/c to is driven by the need to regularize the shape of the Sb2O9 face-sharing octahedral dimers. Ab initio geometry-optimization calculations were used to find a triclinic starting model for Ba3SrSb2O9. [source] Neutron powder diffraction study of orthorhombic and monoclinic defective silicaliteACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2000G. Artioli The crystal structure of silicalite (SiO2) with a substantial amount of structural hydroxyl groups [Si(1,x)O(2,4x)(OH)4x, with 0.08 < x < 0.10] has been refined from neutron powder diffraction data measured using the HRPD instrument at the ISIS pulsed neutron source. Powder data were collected on the as-synthesized orthorhombic sample at 298,K, and on the deuterated monoclinic sample at 100,K. Preferential location of Si-atom vacancies was found on four out of 12 independent T sites in the orthorhombic silicalite [Si(6), Si(7), Si(10) and Si(11)], although the H atoms of the substituting hydroxyl groups could not be located because of the low statistical site occupancy on multiple sites. No significant population of D atoms or of Si vacancies was found in the tetrahedral sites of the monoclinic sample. The detected long-range order of adjacent Si atoms in defective orthorhombic [MFI] structures is compatible with a mechanism of Si vacancy clustering and with the model of hydroxyl nests assumed in the literature on the basis of IR spectroscopic evidence. Crystal data: orthorhombic, Pnma, Z = 8, a = 20.0511,(1), b = 19.8757,(1), c = 13.36823,(9),Å, V = 5327.62,(5),Å3, Dx = 1.798,g,cm,3, Mr = 721.01; monoclinic, P21/n, Z = 4, a = 19.8352,(2), b = 20.0903,(2), c = 13.3588,(1),Å, , = 90.892,(1)°, V = 5322.78,(6),Å3, Dx = 1.799,g,cm,3, Mr = 1442.02. [source] Monoclinic PZN-8%PT [Pb(Zn0.3066Nb0.6133Ti0.08)O3] at 4,KACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2007Jennifer S. Forrester The structure of the relaxor ferroelectric Pb(Zn0.3066Nb0.6133Ti0.08)O3 (lead zinc niobium titanium trioxide), known as PZN-8%PT, was determined at 4,K from very high resolution neutron powder diffraction data. The material is known for its extraordinary piezoelectric properties, which are closely linked to the structure. Pseudo-cubic lattice parameters have led to considerable controversy over the symmetry of the structure. We find the structure to be monoclinic in the space group Cm (No. 8), with the Zn, Nb and Ti cations sharing the octahedrally coordinated B site (site symmetry m, special position 2a) and Pb occupying the 12-coordinate A site (site symmetry m, special position 2a). O atoms occupy a disorted octahedron around the B site (site symmetry m and special position 2a, and site symmetry 1 and general position 4b). Atomic coordinates have been determined for the first time, allowing the direction of spontaneous polarization to be visualized. [source] Tetragonal CeNbO4 at 1073,K in air and in vacuoACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2004Stephen J. Skinner The structure of the high-temperature scheelite-type polymorph of cerium niobium tetraoxide, CeNbO4, has been determined using time-of-flight neutron powder diffraction data collected both in situ at 1073,K in air and in vacuo. In both cases, the structure was found to be tetragonal, with I41/a symmetry and without any significant deviation from the stoichiometric composition. [source] Compressed Octahedral Coordination in Chain Compounds Containing Divalent Copper: Structure and Magnetic Properties of CuFAsF6 and CsCuAlF6CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004Zoran Mazej Dr. Abstract Crystal structures and magnetic investigations of CuFAsF6 and CsCuAlF6 are reported. Together with KCuAlF6, these appear to be the only examples of Jahn,Teller pure CuII compounds containing only one type of ligand that exhibits a compressed octahedral coordination geometry. The Rietveld method has been used for refining the CsCuAlF6 structure based on neutron powder diffraction data at 4 K. The compound crystallizes in space group Pnma (no. 62) with a=7.055(1), b=7.112(1), c=10.153(1) Å and Z=4 at 4 K. The structure is built from infinite [CuF5]n3n, chains of [CuF6]4, octahedra running along the [1,0,0] direction and (AlF6)3, octahedra connected by corners in the trans position, thus giving rise to chains oriented along the [0,1,0] direction. Single crystals of CuFAsF6 were prepared under solvothermal conditions in AsF5 above its critical temperature. The structure was determined from single-crystal data. CuFAsF6 crystallises in the orthorhombic space group Imma (No. 74) with a=10.732(5), b=6.941(3), c=6.814(3) Å and Z=4 at 200 K. The structure can also be described in terms of one-dimensional infinite [CuF5]n3n, chains of tilted [CuF6]4, octahedra linked by trans -vertices running along the b axis. The [CuF5]n3n, chains are connected through [AsF6], units sharing joint vertices. The compressed octahedral coordination of CuII atoms in CuFAsF6 and CsCuAlF6 compounds at room temperature is confirmed by Cu K-edge EXAFS (extended x-ray absorption fine structure) analysis. For both compounds strong antiferromagnetic interactions within the [CuF5]n3n, chains were observed (,p=,290±10 K and ,p=,390±10 K for CuFAsF6 and CsCuAlF6, respectively). The peculiar magnetic behaviour of chain compounds containing divalent copper at low temperature could be related to uncompensated magnetic moments in the one-dimensional network. [source] | ||||||||||