The structure of lithium zirconate (\left(\mathrm{Li}{6} \mathrm{Zr}{2} \mathrm{O}{7}\right)) has been solved by the single-crystal (\mathrm{X})-ray method. (\mathrm{Li}{6} \mathrm{Zr}{2} \mathrm{O}{7}) is monoclinic, space group (C 2 / c) and cell parameters (a=10.440(4), b=5.991(1), c=) (10.204(2) \hat{A}, \beta=100.25(3)^{\circ}, Z=8) (for the asymmetric unit (\mathrm{Li}{3} \mathrm{ZrO}{7 / 2}) ). A least-squares refinement gave conventional and weighted (R) factors of 0.041 and 0.052 , respectively. The structure is of the (\mathrm{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 (\mathrm{Zr}) atom is significantly distorted. A comparison between (\mathrm{Li}{6} \mathrm{Zr}{2} \mathrm{O}{7}) and (\mathrm{Li}{2} \mathrm{ZrO}{3}), another phase of the (\mathrm{NaCl}) type, shows that the structure of the former compound is more "open" than that of (\mathrm{Li}{2} \mathrm{ZrO}_{3}) and, for this reason, a higher mobility of both the (\mathrm{Li}^{+})and (\mathrm{O}^{2-}) ions can be expected for the former phase. These results are in agreement with conductivity measurements. 1993 Academic Press, Inc.