Abstract
The melting and solidification processes of the Bi 1.8Pb 0.4Sr 1.9Ca 2.1Cu 3.5O x in various oxygen atmospheres have been observed in situ using a high-temperature optical microscopy. In the melting process, the samples began to melt at 788°C in N 2, 862°C in 8%O 2+N 2, 880°C in air, 895°C in O 2. Many dark needle-like crystals (Sr,Ca) 2CuO 3 and the white bar-like crystals (Sr,Ca)CuO 2 appeared in the liquid phase. When the temperature was raised, (Sr,Ca)CuO 2 first melted and then (Sr,Ca) 2CuO 3 melted peritectically ((Sr,Ca) 2CuO 3→CaO+L). In the solidification process, two peritectic reactions CaO+L→ (Sr,Ca) 2CuO 3 and (Sr,Ca) 2CuO 3+L→Bi-2212 were observed in the atmospheres of air, 8%O 2+N 2, and O 2, whereas in N 2, only a reaction of L→Bi-2201 was observed.
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