Irreversibility line in optimally doped (T-c approximate to 109 K) and oxygen reduced (T-c approximate to 104 K) Bi1.7Pb0.3Sr2Ca2Cu3O10+delta

We estimated the irreversibility line using de magnetic measurements in an optimally doped (T-c approximate to 109 K) and an oxygen reduced (T-c appro ximate to 104 K) single phase c-axis oriented powder Bi1.7Pb0.3Sr2Ca2Cu3O10 +delta sample. We observed a nearly exponential dependence of H-irr on temp erature for both samples, but close to T-c the slope of the H-irr(T) change s abruptly. The irreversible region of the H vs. T phase diagram extends to higher temperatures for the as-prepared sample. (C) 1999 Elsevier Science B.V. All rights reserved.