CRYSTAL-STRUCTURE OF BA2LA4TI5O18, MEMBER N=6 OF THE HOMOLOGOUS SERIES (BA,LA)(N)TIN-1O3N OF CATION DEFICIENT PEROVSKITE-RELATED COMPOUNDS

Ba2La4Ti5O18 crystallizes in the trigonal system (space group R (3) ov er bar) with the unit-cell parameters: a = 5.584 (1) Angstrom; c = 41. 176 (8) Angstrom; Z = 3. The structure has been solved from single cry stal X-ray diffraction data to a final R-1 = 0.0285. Ba and La atoms a re twelve-fold coordinated and Ti atoms six-fold coordinated. The stru cture can be described as consisting of identical perovskite-like bloc ks, five corner-sharing TiO6 octahedra thick, separated by layers of v acant octahedra. The distortion of the cation and anion sublattices ha s been analysed and a Ba/La order has been evidenced.