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<sub> m </sub>Bi<sub> m+n </sub>O<sub> y </sub> ( 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 (O<sub>2</sub>) = 1 kPa almost do not contain Bi(V), are characterized by an average oxidation number of bismuth Bi<sup>-</sup> = 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<sub> m </sub>Bi<sub> m+n </sub>O<sub> y </sub> oxides are oxidized, as shown by an increase of Bi<sup>-</sup> > 3.06. The final oxidation products at ≈700-20°С are ВаВiO<sub>3</sub> and Ba<sub>4</sub>Bi<sub>1</sub><sup>+</sup><sub>3</sub><sup>3.00</sup>O<sub>23.5</sub> oxides. Perovskite-like Ba<sub> m </sub>Bi<sub> m+n </sub>O<sub> y </sub> oxides with an average oxidation number Bi<sup>-</sup> > 3.06 were not been found. At p (O<sub>2</sub>) = 21-100 kPa, one cannot obtain individual oxides of this series which contain a significant amount of Bi(V) or Bi(V) only.