STUDY OF UPPER CRITICAL-FIELD HC2(T) IN DOPED BI-SR-CA-CU-O SUPERCONDUCTORS WITH 100-K PHASE

Hc2(T) has been studied in four Bi-(Pb)-Sr-Ca-Cu-O superconductors with the 110 K type of structure under magnetic fields up to 12 T. It is found that the curvature of the critical field close to Tc is strongly sample dependent. By a number of measurements which characterize the samples, such as X-ray diffraction, SEM analysis, chemical analysis, AC susceptibility and normal state and superconducting resistive properties, we find that the curvature of Hc2(T) can be empirically correlated with the purity of the samples. It is suggested that the intrinsic behavior of the high-Tc Bi-based polycrystalline superconductors is a linear critical fiels curve close to Tc. © 1990.