Crystal structure of ordered Li₄SiO₄

Abstract

Ordered Li4SiO 4 is monoclinic with space group P2~/m and a = 11.546 (3), b = 6.090 (2), c = 16.645 (3) A, fl = 99.5 (1) °. The substructure is identical to the previously refined structure of Li4SiO4 [V611enkle, Wittman & Nowotny (1968). Monatsh. Chem. 99, 1360-1371 ]. The superstructure was solved and refined to R~ = 6% for 1390 independent reflections. The Li atoms are ordered and occupy 19 of 42 sites in the sevenfold supercell. The LiO 4, LiO 5 and LiO 6 polyhedra are linked by edge- and corner-sharing. There is good three-dimensional connectivity between Li sites at distances of 2.9 A from one another; most Li atoms share edges with at least two adjacent polyhedra. The ordered nature of Li4SiO 4 is consistent with the low ionic conductivity of pure Li4SiO 4 whereas good conductivity of Li4_xSil_xPxO4, Li4_2xSil_xSxO 4 and Li4+xSi~_xAlxO 4 is consistent with the good Li site connectivity and the introduction of either Li vacancies or Li interstitials.