Comparison of cation-ordered P21/c leucite structures with stoichiometry K2X2+Si5O12 (X = Mg, Fe, Co, Zn)

Comparison of cation-ordered P21/c leucite structures with stoichiometry K2X2+Si5O12 (X = Mg, Fe, Co, Zn). A.M.T.Bell (Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield, S1 1WB, UK) and C.M.B.Henderson (School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK). In 1994 we reported [1] the P21/c structure of the leucite analogue K2MgSi5O12. Leucites are silicate framework structures with some of the silicon framework cations partially replaced by divalent or trivalent cations. A monovalent extraframework alkali metal cation is also incorporated in these structures to balance the charges. This K2MgSi5O12 was the first leucite structure with all the silicon and non-silicon framework cations completely ordered onto separate crystallographic sites. This structure had 10 distinct silicon sites and 2 distinct magnesium sites. We have recently refined, using the Rietveld method [2], the P21/c crystal structures of the leucite analogues K2X2+Si5O12, where X = Fe, Co and Zn. These structures are similar to K2MgSi5O12, although incorporation of larger transition metal cations in the place of Mg increases the distortion of the silicate framework structure. [1] Bell, A.M.T., Henderson, C.M.B., Redfern, S.A.T., Cernik, R.J., Champness, P.E., Fitch, A.N. & Kohn, S.C. (1994). Acta Cryst. B50, 31-41. [2] Rietveld, H.M. (1969). J. Appl. Cryst. 2, 65-71.