Phase Relations of the Bi-2201-CuO Pseudobinary Join as a Function of Oxygen Pressure

摘要

Phase relations on the join Bi-2201-CuO have been determined as a function of P(O_2). Most of the major changes that occur between P(O_2) of 1 and 0.01 atm occur in the most oxidizing part of the range. Stoichiometric Bi-2201 occurs only at the most oxidizing conditions and in a narrow temperature range near the solidus. In the Bi-2201-CuO system, the ternary phase that forms has higher Bi:Sr and Cu:Sr than Bi-2201. That phase, Sr_(14)Cu_(24)O_y, and CuO occur in the subsolidus and the invariant point at which they coexist with liquid is a ternary eutectic. The liquid is more Sr-rich than the Bi-2201-CuO join. Decrease in P(O_2) produces a change in the Bi-2201 solid solution so that Stoichiometric Bi-2201 does not occur. At P(O_2) ≤0.5 atm, all Bi-2201 solid solutions have Bi:Cu<2 but Bi:Sr near unity and Sr_(14)Cu_(24)O_y does not form. Small amounts of a phase believed to be Bi_9Sr_(11)Cu_5O_x form under these conditions and the primary phase field of that phase crosses the pseudobinary join and minimum melting is at a ternary tributary reaction point. The liquid there is more Bi-rich than the join. Further decrease in P(O_2) causes a continued freezing point depression and enlargement of the CuO primary phase field so that the compositions of multiply-saturated liquids move away from the CuO apex.