Khalid Boulahya

ITQ-15: The first ultralarge pore zeolite with a bi-directional pore system formed by intersecting 14- and 12-ring channels, and its catalytic implications

The pore topology of ITQ-15 zeolite consists of an ultra-large 14-ring channel that is intersected perpendicularly by a 12-ring pore; acid sites have been introduced in its framework and this unique structure shows advantages over unidirectional ultralarge pore zeolites for diffusing and reacting large molecules.

Synthesis and characterization of the crystal structure and magnetic properties of the ternary manganese vanadate NaMnVO4.

A new ternary manganese vanadate, NaMnVO(4), was synthesized by solid state reaction route, and its crystal structure and magnetic properties were characterized by X-ray diffraction, magnetic susceptibility and specific heat measurements, and by density functional calculations. NaMnVO(4) crystallizes in the maricite-type structure with space group Pnma, a = 9.563(1) A, b = 6.882(1) A, c = 5.316(1) A, and Z = 4. NaMnVO(4) contains MnO(4) chains made up of edge-sharing MnO(6) octahedra, and these chains are interlinked by VO(4) tetrahedra. The magnetic susceptibility has a broad maximum at T(max) = 24 K and follows the Curie-Weiss behavior above 70 K with θ = -62 K. NaMnVO(4) undergoes a three-dimensional antiferromagnetic ordering at T(N) = 11.8 K. The spin exchanges of NaMnVO(4) are dominated by the intrachain antiferromagnetic exchange, and the interchain spin exchanges are spin-frustrated. The most probable magnetic structure of the ordered magnetic state below T(N) was predicted on the basis of the extracted spin exchanges.

The oxycarbonate Ba{sub 3}Co{sub 2}O{sub 6}(CO{sub 3}){sub 0.60} with a 2H-ABO{sub 3}-related structure

The crystal structure of Ba{sub 3}Co{sub 2}O{sub 6}(CO{sub 3}){sub 0.60} has been determined by means of X-ray, neutron and electron diffraction, and high-resolution electron microscopy. This compound has a hexagonal symmetry (space group P{bar 6}) and lattice parameters a = 0.9683(1) and c = 0.95180(8) nm related to the 2H-ABO{sub 3} by means of the expression a = a{sub 2H}(3){sup 1/2} and c = 2c{sub 2H}. It can be described from the ordered intergrowth of two blocks, [Ba{sub 2}Co{sub 2}O{sub 6}]{sup {delta}{minus}} and [Ba(CO{sub 3}){sub 0.60}]{sup {delta}+}, alternating along the a-axis. The first block corresponds to two 2H-like rods and the second one can be related to the BaCO{sub 3} aragonite-type structure. Neutron diffraction data elucidate the relative orientation of carbonate groups along c-axis in the aragonite-like blocks.

Structure evolution with Sr content of the perovskite‐like materials La2−xSrxCoTiO6 (0 ≤x≤ 0.5)

We thank the Spanish Ministerio de Ciencia e Innovacion and Comunidad de Madrid for funding the projects MAT2010-19837-C06-01 and S-2009/PPQ-1626, respectively. Financial support from Universidad CEU San Pablo is also acknowledged. We acknowledge the Spanish Ministerio de Ciencia e Innovacion and Consejo Superior de Investigaciones Cientificas for financial support.

Synthesis and structural characterization of Ba(LnIII2/3BVI1/3)O3 (LnIII=Dy, Gd and Sm; BVI=Mo or W) complex perovskites

Abstract We describe in this work the synthesis and crystal structure of five rare earth and Mo(VI) or W(VI) containing complex perovskites. The compounds studied are Ba(Dy 2/3 Mo 1/3 )O 3 , Ba(Dy 2/3 W 1/3 )O 3 , Ba(Gd 2/3 Mo 1/3 )O 3 , Ba(Gd 2/3 W 1/3 )O 3 and Ba(Sm 2/3 W 1/3 )O 3 and were prepared starting from solutions, by the polymeric precursors method. Structural characterization by HREM, SAED and powder XRD revealed the five compounds to be ordered cubic perovskites, SG Fm -3 m (225), with a cell parameter double of that of a simple perovskite cell and increasing as the size of the trivalent lanthanide ion increases (Dy

A comparative crystal chemical analysis of Ba2CoO4 and BaCoO3

Abstract Polycrystalline Ba2CoO4 has been synthesized by the ceramic method. X-ray and electron diffraction shows this phase to be monoclinic with a=5.8878(4); b=7.6158(6); c=10.3916(8); β=90.738(2). This compound is isostructural to Ba2TiO4 and the structure has been refined from X-ray powder diffraction data by using the Rietveld method. High resolution images interpreted in comparison to simulated images confirm the structure determined by X-ray diffraction. A crystal chemical study based on the cation arrays allows to establish a new relationship between Ba2CoO4 and 2H BaCoO3. Moreover, the Ba subarray seems to be related to the structure of elemental Ba.

New stabilized phases in the Sr/Ca–Mn–Co–O system: structural–magnetic properties relationship

Polycrystalline Sr3CaMn2CoO9 and (Sr0.5Ca0.5)15Mn7Co4O33 have been synthesized and characterised by X-ray and electron diffraction, high resolution electron microscopy and magnetic measurements. These oxides constitute the α = 3, β = 1 and α = 4, β = 1 terms of the homologous series (A3B2O6)α(A3B3O9)β, respectively. Isolated rows of polyhedra sharing faces along the c-axis are made up of units of two and one face-sharing octahedra (occupied by Mn) linked by one trigonal prism (occupied by Co) in an ordered way. The chains are separated by columns of Sr/Ca atoms. Magnetic measurements suggest antiferromagnetic correlations in the two new commensurate monodimensional oxides. The influence of the size of alkaline-earth atoms on the long-range magnetic interactions is discussed.

Structure Determination of the α = 3, β = 6 Term of the (A3B2O6)α(A3B3O9)β Homologous Series (A = Ba, B = Rh) by a Combination of Powder X-ray Diffraction and Electron Microscopy

The α = 3, β = 6 term of the series (A3B2O6)α (A3B3O9)β has been synthesized in polycrystalline form. The structural characterization by powder X-ray diffraction, electron diffraction and high-resolution electron microscopy indicates that this material is isostructural with Ba9Co8O24. In the structure, seven face-sharing octahedra alternate with a trigonal prism defining chains running parallel to the c axis of a rhombohedral unit cell (Rc), with parameters a = 1.00766(4) nm and c = 4.1571(2) nm. The structural refinement shows the presence of a small percentage of Rh vacancies leading to the composition Ba9Rh7.92O24. Pauli paramagnetic behaviour is observed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Strategies to stabilize new members of the (A3A'BO6)α(A3B3O9)β homologous series in the Sr-Rh-O system: Structure of the one-dimensional (α=3,β=2) [Sr10(Sr0.5Rh1.5)TP(Rh6)Oh]O24 oxide

The (α=3, β=2) member of the (A3A′BO6)α (A3B3O9)β homologous series has been stabilised in the Sr-Rh-O system for a [Sr10(Sr0.5Rh1.5)TP(Rh6)Oh]O24 composition. The structural characterisation has been performed by powder X-ray and electron diffraction measurements and high-resolution electron microscopy. In this structure, three face-sharing [RhO6] octahedra linked by one [Rh/SrO6] trigonal prism comprise the infinite one-dimensional chain that runs parallel to the c axis of a trigonal unit cell (Pc1), with parameters a=9.6411(1) and c=21.2440(4) A.

Exploring the physical properties of Eu2SrCo1.5Mn0.5O7, a new n = 2 member of the Ruddlesden–Popper series (Eu,Sr)n+1(Co,Mn)nO3n+1

A new oxide of the Ruddlesden–Popper series has been isolated and structurally characterized in the Eu–Sr–Co–Mn–O system. X-ray diffraction and electron microscopy show that polycrystalline Eu2SrCo1.5Mn0.5O7 constitutes the n = 2 member of a homologous series, the essential feature of which is the existence of two connected Co/Mn octahedral layers, separated by Eu atoms. Electrochemical studies show that the area-specific resistance of this compound is 0.15 Ω cm2 at 700 °C in air, a performance which is comparable to that of the best state-of-the-art materials used as cathodes in intermediate temperature solid oxide fuel cells. Below 150 K the title material presents two different magnetic phenomena. The first one corresponds to the formation of ferromagnetic nanoclusters (TC ∼ 121 K) within an ordered Co2+/Mn4+ atomic configuration, whereas at lower temperature (∼21 K) a spin glass state occurs.