New barium bismuth oxides: BaBi4O7 and BaBi15O23.5

Abstract

New barium bismuth oxides have been synthesized under an argon atmosphere at 530 and 430°C, respectively: a Ba: Bi = 1 : 4 phase has a tetragonal perovskite structure, and a 1 : 15 phase has a rhombohedral structure. For the 1 : 4 phase, the unit cell parameters are a = 4.297(2) A and c = 4.472(2) A as determined by powder X-ray diffraction (XRD). Electron diffraction (ED) patterns show superstructure reflections with the vectors q 1= 1/17[530], q 2 = 1/17[3\(\bar 5\)0], and q 3 = 1/5[002]. These reflections point to an ordered arrangement of barium and bismuth ions in the supercell with the parameters √17a and 5c. The supercell of the 1 : 4 phase includes a ten-layer stack of metal-oxygen planes along the c axis. The rhombohedral 1 : 15 phase has the following hexagonal unit cell parameters as determined by XRD: a= 6.018(2) A, c = 4.070(2) A. In view of the superstructure on the ED patterns, the supercell parameters of the rhombohedral phase are 4a and 2c. The supercell of the 1 : 15 phase contains a six-layer stack of planes along the c axis.