Abstract
Observations are reported on the thermal decomposition of a Pb doped Bi 2Sr 2Ca 2Cu 3O y (Bi-2223) sample. Experimental methods include differential thermal analysis (DTA), thermogravimetric analysis (TGA) using a vacuum balance, and vapor-pressure measurements by Knudsen effusion using (1) mass spectrometry, (2) a vacuum balance, and (3) an external balance for mass transport detection. DTA performed under N 2 showed endothermic peaks at 722°C and 864°C. TGA under vacuum showed mass loss beginning at 700°C with a peak at 750°C. Mass spectrometry showed that O 2(g) was lost from the sample at temperatures between ca. 650°C and 675°C. It was concluded that the DTA peak at 722°C, the mass loss in TGA, and the O 2 loss by mass spectrometry were all associated with a change in oxidation state of Cu from +2 to +1. Vapor pressures of Bi(g) from the Bi-2223 superconductor samples yielded the activity of Bi in the Bi-2223 phase as 0.073 ± 0.016 and the relative chemical potential of Bi in the Bi-2223 phase of −17.4 ± 1.4 kJ/mol at 800 K.
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