STRUCTURAL AND SURFACE-PROPERTIES OF BI-3(MSB(2))O-11 (M=AL, GA)

The structures of the two oxides Bi-3(MSb(2))O-11 (M = Al, Ga) have be en refined by Rietveld-type analysis of combined powder neutron and X- ray synchrotron diffraction data. The two oxides are isostructural, sp ace group Pn (3) over bar, a = 9.43323(4) Angstrom for M = Al and a = 9.48980(3) Angstrom for M = Ga, in which the M and Sb atoms are statis tically distributed in a 12g site. The structures can be described as two interpenetrating networks: a M(2/3)Sb(4/3)O(9) array of edge-shari ng octahedra and a Bi2O3 array of corner-sharing Bi8O4 stellae quadran gulae. There are two independent Bi sites, both having distorted coord ination geometries. The surface composition of both oxides is essentia lly identical to that of the bulk. Comparison with previous studies su ggests that there may be some coupling between the mobility of the Bi ions in these oxides and their electronic properties. (C) 1996 Academi c Press.