Synthesis and crystal structure of new layered perovskite compounds: Li2La0.833(Nb1.5Ti0.5)O-7 and Li2La2.25(Nb1.25Ti2.75)O-13

Single crystals of Li2La0.833(Nb1.5Ti0.5)O-7 and Li2La2.25(Nb1.25Ti2.75)O-1 3 were grown in the system Li2O-La2O3-NPb2O5-TiO2. Both these compounds cry stallize in the space group P4(2)/mnm (No. 136), Z = 4: a = 5.5334(2), c = 18.3907(2) Angstrom and a = 5.4915(6), and c = 33.812(4) Angstrom, respecti vely. Their crystal structures, determined from single crystal X-ray diffra ction data, are related to the Ruddlesden-Popper phases A(n+1)B(n)O(3n+1), which could be better written here as Li-2[A(x)B(n)O(3n+1)]: Li2La0.833(Nb1 .5Ti0.5)O-7 is an n = 2 member and Li2La2.25(Nb1.25Ti2.75)O-13 corresponds to an n = 4 member. In both structures, Nb5+ and Ti4+ ions statistically oc cupy distorted B octahedral sites of the perovskite, La3+ ions partially fi ll the cages of the perovskite, and Li+ ions are found in tetrahedral coord ination between the perovskite layers. (C) 1999 Elsevier Science Ltd.