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 Tl₂Ba₂CuO_x→ Tl₂Ba₂CaCu₂O_x 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.