Critical currents and critical temperatures of oxygenated Tl-2223 bulk superconductors

The thallium based superconductor Tl₂Ba₂Ca₂Cu₃O_y was prepared using a three-step calcination and sintering method. Afterwards, the pellet was two times oxygenated in 740^oC for 20 h. Taking the absorption part of the a.c. susceptibility measurements the critical current density turned out to be from 20 A/cm² before oxygenations, through 380 A/cm² after the first oxygenation to 1120 A/cm² after the second oxygenation. The critical temperature from the dispersion part of the a.c. susceptibility measurements was determined to be 99.7 K, 112.8 K, and 116.2 K respectively.