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Lookup NU author(s): Emeritus Professor Derek Thompson
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The crystal structure of the compound Y2SiAlO5N B-Phase has been determined by X-ray powder diffraction. The data collected from the analysis of the X-ray pattern were used for the electron density mapping of the unit-cell and for Rietveld analysis. It has been shown that the alpha-wollastonite derived structure proposed in the literature, consisting of 2 layers of yttrium cations and three-membered rings of (Si, Al)(O, N)(4) tetrahedra linked together by sharing corners [1], is not correct. Indeed, the Rietveld refinement of this model does not lead to an acceptable result. First, when keeping the bond lengths between the atoms of the tetrahedra to acceptable values, the calculated Xray pattern shows additional peaks with respect to the experimental pattern. On the other hand, if during the refinement the atom sites are allowed to move without any constraint, the final coordinates are strongly shifted by comparison to the initial values so that the tetrahedra seem more chain forming than ring forming. After electron density mapping a new model of the structure has been proposed to refinement and leads to good reliability factors. According to this model the alternative layers of yttrium cations and (Si, Al)(O, N)(4) tetrahedra is confirmed but in this case, the tetrahedra do not form rings but are randomly linked to each other according to a pseudo bidirectional network.
Author(s): Gonon MF, Descamps JC, Cambier F, Thompson DP
Publication type: Article
Publication status: Published
Journal: Materials Science Forum: Characterisation of Nitrides and Oxynitrides
Year: 2000
Volume: 325-3
Pages: 325-333
ISSN (print): 0255-5476
ISSN (electronic):
Publisher: Trans Tech Publications
