A study of cubic bismuth oxides of the type Bi_26−XM_XO_40−δ (M = Ti, Mn, Fe, Co, Ni or Pb) related to γ-Bi₂O₃

A structural investigation of cubic oxides (space group I23) of the formula Bi_26−XM_XO_40−δ (M = Ti, Mn, Fe, Co, Ni and Pb) related to γ-Bi₂O₃ phase has been carried out by the Rietveld profile analysis of high-resolution X-ray powder diffraction data in order to establish the cation distributions. Compositional dependence of the cation distribution has been examined in the case of Bi_26−XCo_XO_40−δ (1 < x < 16). The study reveals that in Bi_26−XM_XO_40−δ with M = Ti, Mn, Fe, Co or Pb, the M cations tend to occupy tetrahedral (2a) sites when X < 2 while the octahedral (24f) sites are shared by the excess Co or Ni cations with Bi atoms when X > 2. Also experimental magnetic moments of Mn, Co and Ni derivatives have been used to establish the valence state and distribution of these cations.