Enhanced irreversibility field and current stabilization by Pb substitution in aligned Tl-1223 high- Tc superconductor

Abstract

Using magnetic methods, we have studied the effects of Pb substitution on the irreversibility line and other features of c-axis aligned Tl based cuprate superconductors with the “1223” structure. Specifically, the properties of (Tl 0.5Pb 0.5)Sr 2Ca 2Cu 3O 9 are compared with those of grain-aligned TlBa 2Ca 2Cu 3O 9 and Tl(BaSr) 2Ca 2Cu 3O 9 materials. The irreversibility line H irr( T) is notably higher for the Pb substituted material ( 1.7 T at 77 K with Hc) and markedly anisotropic for all of the samples. Also, results for the persistent current density are reported. Flux-creep studies of the current-decay rate show that the current is the most stable in the aligned (Tl 0.5Pb 0.5)Sr 2Ca 2Cu 3O 9, and that the decay rate of all three materials increases monotonically as the temperature increases.