Effect of oxygen partial pressure on the Tl2Ba2 CuOx→ Tl2Ba2CaCu2Ox transformation
Abstract
The combined effects of both oxygen partial pressure (Po2) and temperature on the Tl2Ba2CuOx→ Tl2Ba2CaCu2Ox transformation have been investigated for the 2T1 : 2Ba : 1Ca : 2Cu nominal composition in an open reactor. Besides the 2201 and 2212 phases, no other superconducting phases have been observed in the temperature range 860–930°C and the Po2 range 2 × 10–5–1 atm investigated. There is evidence that Po2, plays a key role in the 2201 → 2212 transformation. A nearly pure 2212 single phase is obtained in very narrow temperature ranges depending upon Po2. Lower temperature intervals are always associated with lower Po2 values. This behaviour points to the rapid kinetics of 2212 formation, probably assisted by the presence of a liquid phase. The temperature shift, associated with the predominant intervals of the 2212 phase, is clearly related to the solidus temperature variations (upon Po2) of the superconducting thallium phases.