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Persistent URL http://purl.org/net/epubs/work/34545
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Record Id 34545
Title Structures of Synthetic K2MgSi5 O12 Leucites by Integrated X-ray Powder Diffraction, Electron Diffraction and 29Si MAS NMR Methods
Abstract The structures of disordered and ordered varieties of the title compound have been determined using integrated TEM, MAS NMR and Rietveld analysis of synchrotron X-ray powder diffraction data. Both samples have a 'leucite-like' framework topology. The dry-synthesized sample is cubic, Ia3d [a = 13.4190 (1) angstrom, V = 2416.33 (5) angstrom3] with disordered Mg and Si in tetrahedral framework sites. The hydrothermally synthesized analogue is monoclinic, P2(1)/c [a = 13.168 (5), b = 13.652 (1), c = 13.072 (5) angstrom, beta = 91.69-degrees, V = 2348 (2) angstrom3], and has a fully ordered framework with four K, ten Si and two Mg sites per 24 O atoms (one quarter of the unit cell). Two of these Si sites are linked to Si tetrahedra only [Q4(4Si)], while the other eight Si sites have one Mg and three Si tetrahedra as next-nearest neighbours [Q4(3Si, 1 Mg)]. Q4(4Si) and Mg tetrahedra share opposite comers of four rings. Si and Mg ordering is accompanied by a volume contraction of 2.8%. The X-ray structural data for the ordered sample allow the Si-29 MAS NMR peaks to be assigned to particular Si tetrahedra, and thus to particular values of the mean T-O-T angle. The nature of the polymorphism between the disordered and ordered samples is discussed and related to the different synthesis conditions. Water in the hydrothermal synthesis accelerates Si-Mg ordering, allowing the thermodynamically more stable phase to be formed.
Organisation SRS , 2.3 , SERC
Keywords Materials , Phase Transitions , Crystal Structure , Behavior , Magnesium
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Language English (EN)
Type Details URI(s) Local file(s) Year
Journal Article Acta Crystallogr B 50 (1994): 31-41. doi:10.1107/S0108768193008754 li0152.pdf 1994
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