SUPERCONDUCTIVITY OF THE OXYCARBONATE TL0.5PB0.5SR4CU2CO3O7 - A MAGNETIC STUDY

The magnetic behavior of the 71-K superconductor Tl0.5Pb0.5Sr4Cu2CO3O7 , which consists of an intergrowth of the two nonsuperconducting phase s Sr2CuO2CO3 and Tl0.5Pb0.5Sr2CuO5, has been studied. Its pinning prop erties in terms of the critical current density J(c) and the irreversi bility line have been established using a modified-Bean-model expressi on for the magnetization data and compared to results for other thalli um cuprates. Typical J(c) was calculated to be approximately 8 X 10(6) A/cm2 at 5 K in a field of 0.2 T. The analysis of the reversible magn etization, leading to basic values of the parameters for this oxycarbo nate as lambda(ab)(0) = 170 nm, xi(ab)(0) = 2.39 nm and kappa = 72.5, was also performed. The latter values are compared to other existing d ata especially those concerning the thallium-based superconductors whi ch have been derived from similar analyses. This study shows that the superconducting behavior of this oxycarbonate is closer to multiple co pper layered cuprates than to the single copper layer ''1201'' phase a lthough carbonate groups connect two successive copper layers. It can be considered as intermediate between the thallium bilayer cuprates an d the best lead-doped ''1223'' and ''1212'' superconductors.