LI6ZR2O7, A NEW ANION VACANCY CCP BASED STRUCTURE, DETERMINED BY AB-INITIO POWDER DIFFRACTION METHODS

The structure of Li6Zr2O7, Fw 336.08, has been determined ab initio using Patterson methods on X-ray powder diffraction data and refined using a combination of powder X-ray and neutron diffraction data. Li6Zr2O7 crystallizes in the monoclinic space group C2/c with a = 10.4428(1), b = 5.9877(1), c = 10.2014(1)Å, β = 100.266(1)°, V = 627.67(1)Å3, Z = 4, and Dc = 3.56 g cm-3. The structure is based on a distorted ccp oxygen array with 1 8 of the oxygens missing. Zr and Li adopt a rock salt distribution with Zr in six-coordinate sites but with Li in five-coordinate square pyramidal sites arising from the anion vacancy. The Zr octahedra are arranged in edge-sharing pairs which corner-share with other pairs to give the three-dimensional structure. The lithium square-based pyramids which share edges with the Zr octahedra are arranged in clusters around the anion vacancy. The structure possesses some similarity to the hcp-based ramsdellite structure; the two structures are compared. The final R factors for the combined refinement are Rwp = 10.76%, Rex = 5.01%, χ2 = 4.60 for 53 basic variables with 11,895 observations, corresponding to 535 X-ray and 1264 neutron reflections. © 1993 Academic Press, Inc.