CRYSTALLOGRAPHIC AND MAGNETIC-STRUCTURE OF LI2MNO3

The structure of Li//2MnO//3 was refined on a single crystal: space group C2/m, a equals 493. 7(1), b equals 853. 2(1), c equals 503. 0(2) pm, beta equals 109. 46(3) degree , Z equals 4, R equals 0. 020, R//w equals 0. 027 for 619 independent reflections with I greater than 5 sigma . Distortions in the ordered rocksalt superstructure are induced by the cis positions of Mn**4** plus in the O**2** minus coordination octahedra. Powders of Li//2MnO//3 are slightly disordered with 12 plus or minus 3% Mn on the Li sites. They are antiferromagnetic with T//N equals 36. 5 K; the cell is doubled along c, corresponding to opposite moments on alternating Mn-containing layers along c. A comparison of structural data of rocksalt-related A//2BO//3 compounds (A equals Li, Na; B equals tetravalent metal) shows that many previously reported cells could be indexed in smaller monoclinic or hexagonal cells.