Crystal structure of (Ba1-xLax)[ Mg(1+x)/3Nb(2-x)/3]O3 ceramics

The crystal structure of (Ba1-xLax)[Mg(1+x)/3Nb(2-x)/3]O-3 (BLMN) ceramics with 0 less than or equal to x less than or equal to 1 was investigated using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). When the La content, x, was above 0.1, the 1:2 ordered hexagonal structure found in Ba(Mg1/3Nb2/3)O-3 (BMN) was transformed into the 1:1 ordered cubic structure. The 1:1 ordered cubic structure was maintained up to x = 0.7. When x exceeded 0.7, however, BLMN exhibited a 1: 1 ordered monoclinic structure, rather than a 1:1 ordered cubic structure. La(Mg2/3Nb1/3)O-3 (LMN) has a 1:1 ordered monoclinic P2(1)/n structure with a = 5.6004 Angstrom, b = 5.6414 Angstrom, c = 7.9346 Angstrom, and beta = 89.9819degrees. The monoclinic LMN has the in-phase and the anti-phase tilt of oxygen octahedra. The anti-parallel shift of A-site cations was also found in LMN. (C) 2003 Kluwer Academic Publishers.