Vitrification and Crystallization Processes of High-Tc Superconducting Oxides in the System Bi-Ca-Sr-Cu-O

Abstract

In a relatively wide region of the pseudoternary system BiO_3/2-(CaO⋅SrO)_1/2-CuO, CaO/SrO=1, glassy samples have been obtained by the rapid-quenching technique. The glass transition temperature in this system was found to be mainly dependent on the BiO_3/2 content, with a maximum of 390°C at around 20mol% BiO_3/2. The crystallization of the glasses of proper compositions such as BiCaSrCu₂O_x and Bi₂Ca₂Sr₂Cu₃O_x produced superconductors consisting mainly of the low-T_c (80K) phase; this superconducting phase grew gradually with increasing heat-treatment temperature. The critical temperature T_c (zero) was 86K for Bi₂Ca₂Sr₂Cu₃O_x, whereas it can be expected to be increased by optimizing the heat-treatment conditions and/or using appropriate additives.