Peroxide-based route for the synthesis of zinc titanate powder

In this work the thermodynamical solubility diagrams of zinc and titanium hydroxides were reviewed in order to determine the conditions for maximum degree of phase composition homogenization of precipitates. Experimental investigation of dependency of titanium peroxohydroxide solubility on solution acidity has been carried out and coprecipitation of zinc ions has been studied. It was concluded that precipitation by constant addition of mixed salts and base solutions into the mother liquor with constant acidity of pH 8.5 allows maximizing homogenization of precipitate composition. Thermal treatment process of mixed zinc and titanium hydroxides coprecipitated with hydrogen peroxide was studied using thermogravimetric analysis, differential thermal analysis and X-ray diffraction methods. It was found that precipitates of co-precipitated mixtures of zinc and titanium hydroxides contained impurities of salts precursors of the Zn (NO3)2 and TiOCl2 at a level of 1%. The experimental data demonstrate the influence of hydrogen peroxide on crystal growth rate of the zinc titanate during thermal treatment. The temperature ranges and kinetic parameters of hydroxide mixture dehydration, decomposition of the titanium peroxohydroxide and precursor impurities were determined

Structural exploration on powder diffraction a nice tool for rexamination of phase diagram

The aim of this work is the structural exploration of the La2O3-WO3 phase diagram. Indeed, like many phase diagrams La2O3-WO3 was built in the 70s, but definite compounds structures were not determined and are still unknown. In the present contribution, we focus on La6W2O15, La2WO6 and La14W8O45. These compounds are synthesized as powder by solid state reaction and characterized by X-ray powder diffraction, gravimetric and differential thermal analysis

Ab-Initio Determination of La2Mo4O15 Crystal Structure from X-rays and Neutron Powder Diffraction

International audienceThe structure of La(2)Mo(4)O(15) has been determined from both high resolution X-ray and neutron powder diffraction data. This molybdate crystallizes in a monoclinic space group P2(1)/n with cell parameters a = 9.0357(2) Angstrom, b = 12.7737(2) Angstrom, c = 10.6408(2) Angstrom, beta = 90.2491(6)degrees. The structure consists of molybdenum octahedra [MoO6] and tetrahedra [MoO4], and lanthanum polyhedra [LaO9], Molybdenum polyhedra are connected: together, forming large units [Mo6O22], isolated by lanthanum polyhedral chains, This structure is compared with those of already known lanthanide molybdates with formula Ln(2)Mo(4)O(15) (Ln = Ce, Ho)

Ab Initio Determination of the Novel Perovskite-Related Structure of La7Mo7O30 from Powder Diffraction

International audienceA new mixed valence molybdate, La7Mo7O30, first prepared by high energy ball milling, has been successfully synthesized by controlled hydrogen reduction of La2Mo2O9. Its original crystal structure was determined from X-ray and neutron powder diffraction (space group R-(3 over bar); a = b = 17.0051(2) Angstrom, 6.8607(1) Angstrom; Z = 3;; reliability factors: R-p = 0.081, R-wp = 0.091, chi(2) = 3.1, R-Bragg = 0.049, R-F = 0.033). It consists in the hexagonal stacking of individual cylinders of perovskite-type arrangement. These cylinders are built up from perovskite cages sharing corners in trans-position along their diagonal axis. Two different mixed-valence molybdenum sites coexist, with more (Mo+5.75) Or less (Mo+4.5) distorted octahedral environments. Lanthanum atoms are located within the perovskite cages and around them, very close to their regular positions in the perovskite structure. Lanthanum and molybdenum atoms thus form two rows of almost perfect cubes, shifted from each other by c/2. An electron microscopy study revealed the defect-free cationic and octahedral arrangements in the (a,b) plane

Effects of Partial Substitution of Mo6+ by Cr6+ and W6+ on the Crystal Structure of the Fast Oxide-Ion Conductor La2Mo2O9

International audienceThe crystal structure of the solid solutions La2Mo2-yCryO9 (y≤0.5) and La2Mo2-yWyO9 (y≤1.4) has been studied using X-ray and neutron powder diffraction. These two series of lanthanum molybdates, which belong to the LAMOX family of fast oxide-ion conductors, exhibit a different structural behavior depending on the substituting element. The Cr series follows a regular Vegard-type evolution of crystallographic parameters. However, the behavior of theWseries is different, the lattice constant varying in a nonlinear fashion with substitution level, resulting in a smaller cell volume for higher tungsten contents, despite the larger ionic radius of tungsten. Two main structural effects are evidenced: a variation in the distribution of ligands around tungsten, made apparent through the changing balance of oxygen O2 and O3 site occupancies along the series, and a nonlinear evolution of interatomic distances and angles involving the O1 oxygen site. An alternative structural description, based on [O1La3Mo] antitetrahedra, is proposed in order to better account for the transport properties of these materials

Effect of deposition conditions on microstructure of LiPON films obtained by rf magnetron sputtering

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Room-temperature synthesis of a new stable (N 2 H 4 )WO 3 compound: a route for hydrazine trapping

International audienceA new (N2H4)WO3 compound has been obtained by mixing WO3 and aqueous hydrazine solution at room temperature for 24 h. The reaction is catalyzed by the presence of lithium. X-ray, synchrotron and neutron diffraction techniques have shown that the material crystallizes in trigonal space group P3221 (No. 154). Chains of distorted WO4 tetrahedra extend along the a axis of the unit cell, linked by a corner-sharing oxygen atom: the N2H4 are in the voids between them. The thermal characterization shows that this new compound is stable up to 220°C, greatly beyond the boiling point of N2H4 (114°C); thus making it a promising candidate for catalysis or trapping applications