CRYSTAL-STRUCTURE OF BI2O4 WITH BETA-SB2O4-TYPE STRUCTURE

A new mixed valent bismuth oxide, Bi3+Bi5+O4, was prepared by a low te mperature hydrothermal reaction using a hydrated sodium bismuth oxide, NaBiO3 . nH(2)O, as a starting material. This oxide is isostructural with beta-Sb2O4 and the lattice parameters are a = 12.3668(2), b = 5.1 180(1), c = 5.5670(1) Angstrom and beta = 107.838(1)degrees in the mon oclinic system. The crystal structure was refined using high resolutio n neutron powder diffraction data resulting in R(WP) = 7.76, R(P) = 6. 01, R(E) = 5.98, and R(I) = 2.02%. In this mixed valent bismuth oxide, Bi3+ and Bi5+ occupy distinct crystallographic sites, Bi3+ being coor dinated by eight oxygens and Bi5+ being octahedrally coordinated by si x oxygens. The structure can be related to the CaF2-type structure. Th is mixed valent bismuth oxide decomposes to Bi2O3 via an intermediate phase with mixed valent states with weight loss caused by reduction of Bi5+ to Bi3+ at elevated temperatures. (C) 1995 Academic Press, Inc.