AN ELECTRON-DIFFRACTION STUDY OF THE TYPE-II BI2-XNBXO3+X SOLID-SOLUTION

The structural chemistry of the type II Bi2-xNbxO3+x solid solution has been studied via computer simulation of the electron diffraction patterns. The Nb cations were found to exist in some Nb7O30 and Nb18O72 clusters which were in partially ordered arrangements in the delta-Bi2O3 matrix, forming some incommensurate superstructures. Commensurate 11 x 11 x 11 superstructures in Bi17Nb3O33, Bi9NbO16, and an 8 x 8 x 8 superstructure in Bi4NbO8.5 derived from the delta-Bi2O3 subcell have been proposed in order to approach the real structures. (C) 1995 Academic Press, Inc.