Role of Oxygen in the Formation of Perovskite-Like Oxides of Homologous Series Ba<sub><i>m</i></sub>Bi<sub><i>m+n</i></sub>O<sub><i>y</i></sub> (<i>m </i>= 1-9; <i>n </i>= 0-3, 5, 7, 9)
The effect of synthesis conditions on the phase composition and valence state of bismuth in perovskite-like oxides of Ba m Bi m+n O y  ( m = 1-9; n = 0-3, 5, 7, 9) homologous series was studied by X-ray diffraction and chemical analyses. The oxides synthesized at p (O2) = 1 kPa almost do not contain Bi(V), are characterized by an average oxidation number of bismuth Bi- = 3.00-3.01, and, consequently, are stoichiometric in oxygen content. These phases are thermodynamically stable from the crystallization region to 20°C. Under cooling below the solidus line, Ba m Bi m+n O y  oxides are oxidized, as shown by an increase of Bi- > 3.06. The final oxidation products at ≈700-20°С are ВаВiO3 and Ba4Bi1+33.00O23.5 oxides. Perovskite-like Ba m Bi m+n O y  oxides with an average oxidation number Bi- > 3.06 were not been found. At p (O2) = 21-100 kPa, one cannot obtain individual oxides of this series which contain a significant amount of Bi(V) or Bi(V) only.