A rietveld analysis of the crystal structure of ammonioleucite

The crystal structure of ammonioleucite was refined by a Rietveld analysis using X-ray diffraction data of the type specimen. The refinement with a space group I4l/a was converged at Rwp=12.12, Rp=9.39, RF=4.86, RB=7.71, and Re=2.55% with lattice parameters of a=13.2106(6) and c=13.7210(7) A. Ammonioleucite is isostructural with leucite. The (Si, Al)O4 tetrahedra form 4-, 6-, and 8-membered rings by sharing their apical oxygen atoms. The crystal structure consists of the three-dimensional framework of the rings of the tetrahedra. Ammonium ions are located in cavities in the framework. The (NH4)+ ions in these cavities are larger than the corresponding K+ ions in leucite, causing the cavities to be enlarged relative to those in leucite. Among the 4-, 6-, and 8-membered rings of (Si,Al)O4 tetrahedra, only the 8-membered rings have diameters large enough to allow the migration of exchangeable K+, (NH4)+ and Na+ ions.