A Single-Crystal X-Ray Diffraction Study of Lithium Zirconate, Li6Zr2O7, a Solid-State Ionic Conductor

The structure of lithium zirconate (Li6Zr2O7) has been solved by the single-crystal X-ray method. Li6Zr2O7 is monoclinic, space group C2/c and cell parameters a = 10.440(4), b = 5.991(1), c = 10.204(2) Å, β = 100.25(3)°, Z = 8 (for the asymmetric unit Li3ZrO7/2). A least-squares refinement gave conventional and weighted R factors of 0.041 and 0.052, respectively. The structure is of the NaCl type and is characterized by an ordered anionic deficiency. As a consequence the coordination number of the Li atoms is 5, with the coordination geometry of a distorted square pyramid. Also, the oxygen octahedron around each Zr atom is significantly distorted. A comparison between Li6Zr2O7 and Li2ZrO3, another phase of the NaCl type, shows that the structure of the former compound is more "open" than that of Li2ZrO3 and, for this reason, a higher mobility of both the Li+ and O2- ions can be expected for the former phase. These results are in agreement with conductivity measurements