COLUMNAR DEFECTS AND IRREVERSIBILITY LINES IN TL-BASED SUPERCONDUCTORS

Tl-based superconducting ceramics of different phases (Tl-2212, Tl-122 3, Tl-2223) have been irradiated by heavy ions (6 GeV Pb and U). It is shown by high resolution electron microscopy that Pb irradiations ind uce columnar defects of about the same diameter (95 +/- 5) Angstrom in Tl-2223 and Tl-1223 whereas a larger dispersion of the diameter aroun d the value of 95 Angstrom is ohserved for Tl-2212. The U irradiation leads to diameters slightly more scattered than in the Pb irradiation. These samples have been studied by SQUID magnetometry before and afte r irradiation. Drastic increases of the critical current induced by th e irradiation have been observed and the 'hierarchy' existing between phases about the location of their irreversibility lines remains the s ame after irradiation at the same fluence.