Li 6Zr 2O 7, a New Anion Vacancy ccp Based Structure, Determined by ab initio Powder Diffraction Methods

Abstract

The structure of Li 6Zr 2O 7, 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. Li 6Zr 2O 7 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)Å 3, Z = 4, and D c = 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 R wp = 10.76%, R ex = 5.01%, χ 2 = 4.60 for 53 basic variables with 11,895 observations, corresponding to 535 X-ray and 1264 neutron reflections.