Si-Al ordering in leucite group minerals and ion-exchanged analogues; an MAS NMR study

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Other| December 01, 1997 Si-Al ordering in leucite group minerals and ion-exchanged analogues; an MAS NMR study Simon C. Kohn; Simon C. Kohn University of Warwick, Department of Physics, Coventry, United Kingdom Search for other works by this author on: GSW Google Scholar C. Michael Henderson; C. Michael Henderson Search for other works by this author on: GSW Google Scholar Raymond Dupree Raymond Dupree Search for other works by this author on: GSW Google Scholar American Mineralogist (1997) 82 (11-12): 1133–1140. https://doi.org/10.2138/am-1997-11-1211 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Simon C. Kohn, C. Michael Henderson, Raymond Dupree; Si-Al ordering in leucite group minerals and ion-exchanged analogues; an MAS NMR study. American Mineralogist 1997;; 82 (11-12): 1133–1140. doi: https://doi.org/10.2138/am-1997-11-1211 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Two series of leucite group materials, with K, Rb, and Cs as extra-framework cations, have been synthesized by ion exchange from a natural well-ordered analcite and a natural disordered leucite. 29Si and 27Al MAS NMR data for the analcite-derived series provide complementary information on tetrahedral cation ordering. The ordering in terms of the number of Al next-nearest neighbors, Q4(nAl) (short-range order), does not change significantly during ion exchange, indicating that Al and Si remain essentially fixed in their original positions. In contrast, the ordering of Al over T1, T2, and T3 (long-range order) for the analcite-derived series changes dramatically with changing alkali cation; the Al occupancies for the three analcite-derived samples expressed as T1:T2:T3 are approximately 0.25:0.50:0.25 for KAlSi2O6, 0.40:0.20:0.40 for RbAlSi2O6, and 0.15:0.70:0.15 for CsAlSi2O6. During the ion exchange, at temperatures above the cubic-tetragonal phase transitions, only one symmetrically distinct T site is present. It is proposed that on cooling through the cubic-tetragonal phase transition the structure collapses around the non-framework cations to give the lowest energy Si-Al distribution over the three T sites irrespective of the original T-site ordering in the starting material. Our data suggest that the identity of the cation in the W site affects the orientation of the framework distortions associated with the cubic-tetragonal phase transition and leads to the possibility that a particular tetrahedral cation site can take on the characteristics of a T1, T2, or T3 site. The data and their interpretation have important implications for the mechanism of this type of structural phase transition. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.