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|Title:||Crystal Structure and Thermal Expansion of the Low- and High- temperature Forms of BaMIV(PO4)2 Compounds (M ¼ Ti, Zr,HfandSn)|
|Authors:||BREGIROUX D.; JARDIN R.; POPA Karin; RAISON Philippe; WALLEZ G; QUARTON M; BRUNELLI M.|
|Citation:||JOURNAL OF SOLID STATE CHEMISTRY vol. 182 p. 1115-1120|
|Publisher:||ACADEMIC PRESS INC ELSEVIER SCIENCE|
|Type:||Articles in periodicals and books|
|Abstract:||The crystal structure of b-BaZr(PO4)2, archetype of the high-temperature forms of BaM(PO4)2 phosphates (with M=Ti, Zr, Hf and Sn), has been solved ab initio by Rietveld analysis from synchrotron X-ray powder diffraction data. The phase transition appears as a topotactic modification of the monoclinic (S.G. C2/m) lamellar a-structure into a trigonal one(S.G. P3m1) through a simple mechanism involving the unfolding of the [Zr(PO4)2]n2- layers. The thermal expansion is very anisotropic (e.g., -4.1 < ai < 34.0 x 10-6 K-1 in the case of a-BaZr(PO4)2) and quite different in the two forms, as a consequence of symmetry. It stems from a complex combination of several mechanisms, involving bridging oxygen rocking in M¿O¿P linkages, and ¿¿bond thermal expansion¿¿.|
|JRC Institute:||Institute for Transuranium Elements|
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