title: Rietveld refinement of the crystal structures of Rb2 XSi5O12 (X = Ni, Mn).
abstract: The synthetic leucite silicate framework mineral analogues Rb2 XSi5O12 {X = Ni [dirubidium nickel(II) penta-silicate] and Mn [dirubidium manganese(II) penta-silicate]} have been prepared by high-temperature solid-state synthesis. The results of Rietveld refinements, using X-ray powder diffraction data collected using Cu Kα X-rays, show that the title compounds crystallize in the space group Pbca and adopt the cation-ordered structure of Cs2CdSi5O12 and other leucites. The structures consist of tetra-hedral SiO4 and XO4 units sharing corners to form a partially substituted silicate framework. Extraframework Rb(+) cations sit in channels in the framework. All atoms occupy the 8c general position for this space group. In these refined structures, silicon and X atoms are ordered onto separate tetra-hedrally coordinated sites (T-sites). However, the Ni displacement parameter and the Ni-O bond lengths suggest that for the X = Ni sample, there may actually be some T-site cation disorder.
authors.affiliation: Materials and Engineering Research Institute (MERI), Sheffield Hallam University, Sheffield S1 1WB, England.
authors.forename: Anthony M T
authors.initials: AM
authors.lastname: Bell
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, England; ASTeC, Sci-Tech Daresbury Laboratory, Science and Technology Facilities Council, Warrington WA4 4AD, England.
authors.forename: C Michael B
authors.initials: CM
authors.lastname: Henderson
keywords: cation-ordered structure; leucite minerals; powder diffraction; silicate framework minerals