On the Role of Oxygen in Phase Formation Involving Oxides of the Ba_{m + n}Bi_mO_y (m = 1–10; n = 0–5, 7–9, 11, 13, 17) Homologous Series

Abstract—

The role of oxygen in the synthesis and phase formation of perovskite-like oxides of the homologous series Ba_{m + n}Bi_mO_y (m = 1–10; n = 0–5, 7–9, 11, 13, 17) is discussed. X-ray diffraction and chemical analysis show that Ba_{m + n}Bi_mO_y oxides are formed in air in the presence of an oxidizing agent (oxygen) through the initial stage of formation of Bi(V) enriched phases. At this synthesis stage, the Ba : Bi 17 : 9–5 : 4 samples are of the two-phase type and consist of Ba₂Bi^+4.78O_4.39 and BaBiO₃ oxides. With an increase in the temperature, the samples first undergo solid-phase transformations into Ba : Bi 9 : 4, 5 : 2, 21 : 8 oxides, and in the liquidus–solidus region, liquid-phase transformations occur with the reduction of Bi(V) → Bi(III) and oxygen loss in the presence of oxygen-deficient phases. When cooling the oxygen-deficient Ba–Bi–O melt ($\overline {{\text{Bi}}}$ = 3.00–3.06), oxygen is absorbed, as evidenced by an increase in the average degree of bismuth oxidation with a decrease in the annealing temperature due to the oxidation of Bi(III) → Bi(V). Cooling samples of Ba : Bi 25 : 8, 11 : 4, 21 : 8, 5 : 2, 9 : 4, and 2 : 1 to 20°C results in their complete saturation with oxygen; phases 25 : 8, 11 : 4, and 5 : 2 can be obtained almost completely oxidized ($\overline {{\text{Bi}}}$ = 4.95–5.00).