STRUCTURAL DESCRIPTION OF LA3NBO7

The structure of La3NbO7 was refined on a single crystal prepared by t he flux method (R = 0.029). The unit cell is orthorhombic, with lattic e parameters a = 7.747(1) Angstrom, b = 11.149(1) Angstrom, c = 7.611( 1) Angstrom and centrosymmetric space group Pnma, Z = 4. Similarly to the previous structural description proposed in the Cmcm space group ( 1), the stacking is described in terms of zigzag chains of NbO6 octahe dra aligned along the a axis of the crystal. The lanthanum ions lie on two different sites, for which the coordination polyhedra consist in 7 or 8 oxygen neighbors and the Nb atoms are off-centered in their oct ahedra. (C) 1995 Academic Press, Inc.