A STUDY OF CUBIC BISMUTH OXIDES OF THE TYPE BI(26-X)M(X)O(40-DELTA) (M=TI, MN, FE, CO, NI OR PB) RELATED TO GAMMA-BI2O3

A structural investigation of cubic oxides (space group I23) of the fo rmula Bi(26-x)M(x)O(40-delta) (M = Ti, Mn, Fe, Co, Ni and Pb) related to the Y-Bi2O3 phase has been carried out by the Rietveld profile anal ysis of high-resolution X-ray powder diffraction data in order to esta blish the cation distributions. Compositional dependence of the cation distribution has been examined in the case of Bi26-xCoxO40-delta (1 < x < 16). The study reveals that in Bi(26-X)M(X)O(40-delta) with M = T i, Mn, Fe, Co or Pb, the M cations tend to occupy tetrahedral (2a) sit es when x < 2 while the octahedral (24f) sites are shared by the exces s Co or Ni cations with Bi atoms when x > 2. Also experimental magneti c moments of Mn, Co and Ni derivatives have been used to establish the valence state and distribution of these cations.