The Formation Process of New High-T_c Superconductors with Single-Layer Thallium-Oxide, TlBa₂Ca₂Cu₃O_y and TlBa₂Ca₃Cu₄O_y

Abstract

The formation process of new high- T c superconductors with a single Tl-O layer, TlBa 2 Ca 2 Cu 3 O y (1223 phase) and TlBa 2 Ca 3 Cu 4 O y (1234 phase), was studied. The thallium content decreased continuously with increased sintering time. At the first sintering stage, the Tl 2 Ba 2 Ca 2 Cu 3 O y phase (2223 phase) was formed. Next, the 1223 phase was formed with the demise of the 2223 phase. Then, after further sintering, the 1234 phase was formed with the disappearance of the 1223 phase. These results indicate that one Tl-O layer of the double Tl-O layers of the 2223 phase evaporated owing to the volatility of the thallium component, and the 1223 phase was formed. Then the 1223 phase with three Cu-O layers changed to the stable 1234 phase with four Cu-O layers.