Role of Oxygen in the Formation of Perovskite-Like Oxides of the Ba_mBi_m+nO_y Homologous Series (m = 1–9; n = 0–3, 5, 7, 9)

Abstract

The effect of synthesis conditions on the phase composition and valence state of bismuth in perovskite-like oxides of the Ba_mBi_m+nO_y (m = 1–9; n = 0–3, 5, 7, 9) homologous series has been studied by means of X-ray diffraction and chemical analysis. The oxides synthesized at p(O₂) = 1 kPa almost have not contained Bi(V), have been characterized by average oxidation number of bismuth $\overline {{\rm{Bi}}}$ = 3.00–3.01 and, consequently, have been stoichiometric in oxygen content. These phases have been thermodynamically stable from the crystallization region to 20°C. Under cooling below the solidus line, the Ba_mBi_m+nO_y oxides have been oxidized, as shown by increase in $\overline {{\rm{Bi}}}$ to above 3.06. The final oxidation products at ≈700–20°С have been ВаВiO₃ and Ba₄Bi₁⁺₃^3.00O_23.5 oxides. Perovskite-like Ba_mBi_m+nO_y oxides with average oxidation number $\overline {{\rm{Bi}}}$ > 3.06 have not been found. At p(O₂) = 21–100 kPa, individual oxides of this series which contain significant amount of Bi(V) or exclusively Bi(V) cannot be obtained.