Doping states and irreversibility fields of high-pressure-synthesized (Tl,Cu)Sr2Ca2Cu3Oy superconductors

The effects of Cu substitution for Tl in TlSr2Ca2Cu3Oy. superconductor were investigated. Nearly single-phase samples of T1-xCuxSr2Ca2Cu3Oy (x = 0.2 - 0.6) were successfully synthesized using a high pressure technique. The ob served shrinkage in the lattice parameter a, concave rho -Tl curve above T- c and negative thermoelectric power near room temperature indicated that th e Cu-substituted samples were over-doped. T-c for the sample with x = 0.4 i ncreased from 73 to 94 K after annealing treatment in flowing argon gas. Th e Cu-substituted samples showed lower irreversibility field B-irr as a func tion of reduced temperature than that of the pristine TlSr2Ca2Cu3Oy. [Physi ca C 324 (1999) 15]. (C) 2001 Elsevier Science B.V. All rights reserved.