Single-crystal X-ray diffraction studies of homologues in the series nBa(Nb, Zr)O3+3mNbO with n=2, 3, 4, 5 and m=1

Single crystals of four homologues in the series nBa(Nb, Zr)O-3 + 3mNbO, with n:m = 2:1, 3:1, 4:1, and 5:1, were found in the reduced Ba-Nb-Zr-O system. Single-crystal X-ray diffraction data were collected for all the crystals, For all homologues the space group was found to be P4/mmm. The structures can be described as intergrowths of Ba(Nb,Zr)O-3 perovskite and NbO slabs. The refined cell parameters and compositions of the 2:1, 3:1, and 4:1 homologues are a = 4.1768(5) Angstrom and c = 12.269(2) Angstrom for Ba2Nb4.5(1)Zr0.5(1)O9, a = 4.1769(5) Angstrom and c = 16.493(3) Angstrom for Ba3+deltaNb4.8(2)-delta Zr1.2(2)O12-delta (delta = 0,098(4)), and c = 20.619(4) Angstrom for Ba4+deltaNb5.1(4)-deltaZr1.9(4)O15-delta (delta = 0.270(9)). The refined cell parameters of the 5:1 homologue are a = 4.1727(3) Angstrom and c = 24.804(3) Angstrom. Zr replaces Nb only in the NbO, octahedra found in the perovskite slabs. (C) 2001 Academic Press.