La(Li1/3Ti2/3)O3:: a new 1:2 ordered perovskite

A new 1:2 ordered perovskite La(Li1/3Ti2/3)O-3 has been synthesized via solid-state techniques. At temperature > 1185degreesC, Li and Ti are randomly distributed on the B-sites and the X-ray powder patterns can be indexed in a tilted (b(-)b(-)c(+)) Pbnm orthorhombic cell (a = a(c)root2 = 5.545 Angstrom, b = a(c)root2 = 5.561 Angstrom, c = 2a(c) = 7.835Angstrom). However, for T less than or equal to 1175degreesC, a 1:2 layered ordering of Li and Ti along <III>(c) yields a structure with a P2(1)/c monoclinic cell with a = a(c)root6 = 9.604 Angstrom, b = a(c)root2 = 5.552 Angstrom, c = a(c)3root2= 16.661 Angstrom, beta = 125.12degrees. While this type of order is well known in the A(2+) (B1/32+B2/35+)O-3 family of niobates and tantalates, La(Li1/3Ti2/3)O-3 is the first example of a titanate perovskite with a 1:2 ordering of cations on the B-sites. (C) 2002 Elsevier Science (USA). All rights reserved.