MAGNETIC AND THERMAL-PROPERTIES OF THE 116K SUPERCONDUCTOR TL-1223

The (Tl,Pb,Bi)(1)(Sr,Ba)(2)Ca2Cu3O9 (Tl-1223) superconducting phase is characterized by means of X-ray diffraction, SEM and optical microgra phs, AC susceptibility, resistivity, magnetization M(T, H) both in the reversible and in the irreversible regime up to 5 T, and specific hea t near T-c up to 14 T. Reversible magnetization data are analyzed usin g the London model in the low field limit, and the lower critical fiel d is determined from the first flux penetration. Values are given for the upper critical field, mu(0)H(c2c)(0) = 75 T, the thermodynamic cri tical field, mu(0)H(c)(0) = 0.81 T, the lower critical field, mu(0)H(c 1c)(0) = 0.037 T, the penetration depth, lambda(ab)(0) = 1370 Angstrom , the Ginzburg-Landau parameter, kappa(T-c) = 45, kappa(0) = 65, and f or the mean-field specific heat jump, Delta C/T-c = 18 mJ/(K-2 mol). T he variation of the entropy with the field is measured near T-c and ag rees with magnetization data, thus demonstrating equilibrium condition s. Large magnetic hysteresis is observed only at temperatures below 20 K. The irreversibility line in the high temperature regime follows th e functional dependence H-irr(T) proportional to (1 - T/T-c)(2). A sys tematic departure from this behaviour is observed below 70 K, possibly as a result of a phase transformation in the vortex system.