Study of small distorsions in Bi12MO20 oxides by simple exafs transmission technics

International audienceIn some Bi12 [A+xα B+yβ]O20 sillenite type phases the interatomic distances between oxygen and A or B cations located in tetrahedral sites of the lattice can be determined by EXAFS despite difficult recording conditions due to relatively low concentrations of A and B species in presence of strong absorbing bismuth

Effect of Dopants on Zirconia Stabilization—An X-ray Absorption Study: I, Trivalent Dopants

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65562/1/j.1151-2916.1994.tb06964.x.pd

Modification des interfaces dans des multicouches TiN/AlN : effet du bombardement ionique

International audienc

CHALCOGENIDE AND OXYCHALCOGENIDE GLASSES : EVOLUTION OF THE GALLIUM SURROUNDING WITH THE OXYGEN CONTENT

L'analyse structurale des verres de sulfure de terre rare par EXAFS met en évidence un environnement sulfuré tétraédrique pour le gallium. Lorsqu'on opère une substitution partielle du soufre par l'oxygène, cet environnement évolue : le gallium se place dans des sites octaédriques distordus. De plus, nous avons pu préparer un matériau existant à la même composition dans les deux états, vitreux et cristallin ; l'analyse a alors révélé un polyèdre de coordination plus régulier dans l'état vitreux.Structural analysis of rare earth sulfide glasses shows a sulfur tetrahedral surrounding for the gallium atom When sulfur is substituted by oxygen this surrounding changes : gallium occupies excentred position in octahedral sites. Moreover, we could prepare a material within the two states (glassy and crystalline) for an identical composition : analysis revealed a more regular coordination polyhedron for the glass

Etude par EXAFS et fluorescence X de photocatalyseurs zéolithiques renfermant des nanoparticules de ZnO

Nous présentons les premiers résultats obtenus par spectroscopie d'absorption X au seuil K du zinc et d'émission X sur la structure atomique de clusters formés à partir de zinc et d'oxygène, confinés à l'intérieur des cavités de la sodalite. Nous avons commencé par une étude de la structure des références ZnAl2O4 et ZnO. Les résultats obtenus sont en bon accord avec les données cristallographiques. Dans le cas des échantillons de sodalite, le zinc est entouré en premiers voisins par de l'oxygène dans un environnement tétraédrique ; la distance Zn-O est de 1.97 Å. En seconds et troisièmes voisins le zinc est entouré par de l'aluminium et du zinc respectivement à des distances Zn-Al de 2.86 Å et Zn-Zn de 3.38 Å. Une étude de l'influence de la température de calcination a également été faite. Ces résultats ont permis la mise en évidence d'une forte interaction des clusters avec la charpente.The first results on ZnK X-ray emission and Zn K EXAFS studies of ZnO clusters confined inside the cages of sodalite are reported here. The analysis of the first, second and third shells of coordination around Zn in ZnO and ZnAl2O4 references is presented. The results agree fairly well with the crystallographic data. In sodalite samples, the Zn atoms are in tetrahedral coordination with oxygen at 1.97 Å. The second and third neighbours of Zn are Al at 2.86 Å and Zn at 3.38 Å respectively, the former belonging to the sodalite framework. The influence of the calcination temperature on the local order around Zn is also discussed. Interaction between the clusters and the framework is clearly evidenced

Structural Study of Interlayer Zr Particles in Exchanged and Pillared Beidellite

Zirconia pillared clays (with synthetic beidellite as host material) were prepared by replacing the sodium interlayer cations by zirconium hydroxy polycations, and then heating to stabilize the structure. The pillaring solution was an aqueous solution of zirconyl chloride, but the structure of the polycation which is intercalated remains unknown. From the XRD data. the interlayer spacing was found to be 9 Å in Zr exchanged beidellite and slightly lower (7Å) after calcination. The local environment of zirconium in solid zirconyl chloride and in the pillaring solution was first examined and then in the ion-exchanged and calcined beidellite. The EXAFS results for zirconyl chloride in the solid state and in aqueous solution, showed that the nearest neighbours and the next-nearest-neighbours environments of Zr are identical in solid and in solution. In the Zr-exchanged beidellite, the Zr cations have the same environment as in the pillaring solution. On the opposite. the mean Zr-O and Zr-Zr distances in the calcined sample are shortened with respect to Zr-exchanged beidellite

Evolution de la structure cristalline et des propriétés mécaniques de nitrure Ti1-xAlxN en fonction de la teneur en Al

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Adhesion of rhodium films on metallic substrates

Rhodium coated metallic films were prepared by magnetron sputtering on metallic substrates. All films were elaborated in same conditions on copper, molybdenum and stainless steel. Adhesion strength tests were carried out by scratch test. The results reveal that the adhesion strength between the film and the substrate is influenced by the hardness of the substrate. Increase of deposition temperature improves the adhesion of the coating. In addition, pre-treatment of substrates by a filtered cathodic vacuum arc and the layer thickness have has some effects on the final adhesion strength. (c) 2008 Elsevier B.V. All rights reserved