Average and super structure ofβeucryptite (LiAlSiO4) Part I. Average structure*

Abstract

β eucryptite, Li₂O · Al₂O₃ · 2SiO₂, has a high-quartz-like structure. It crystallizes in the space group P6₂22. X-ray diffraction photographs of single crystals show, besides the main reflections of a high-quartz-like subcell, superstructure reflections which lead to doubling of the lattice constants of the subcell. The intensities of the main reflections were used to investigate the average structure and its likeness to the ideal high-quartz structure, which was used as the starting model for the structure refinement. The Li atoms are located in the main channels parallel to the c axis. They are coordinated by four oxygen atoms. The “thermal” vibrational ellipsoid of the oxygen atoms shows an unusually large main axis of 0.2 Å, due to the superstructure (cf. part II). The mean (Si, Al) –O distance is 1.68 Å, the final unweighted R value is 0.050.