The effects of the sintering schedule on the superconducting properties of Bi(Pb)-Sr-Ca-Cu-O thick films

Abstract

Superconducting Bi(Pb)-Sr-Ca-Cu-O powders were prepared by the emulsion drying method. The powders consisting of low-Tc phase (Bi(Pb)2Sr2Ca1Cu2Oy) and a small amount of Ca2PbO4 were prepared by calcining in low oxygen partial pressure at 800 degrees C. Bi(Pb)-Sr-Ca-Cu-O thick films on single crystal MgO(100) substrates were fabricated with the calcined powder using a screen-printing technique to study the effect of the sintering schedule on the superconducting phase formation and properties. The films sintered at 830 degrees C consisted of the mixture of the low-Tc phase and the high-Tc phase even though the sintering was done over 90 h (normal sintering). The high-Tc phase was formed quickly in the films sintered with a step sintering schedule sintering at 840 degrees C for 4 h and at 830 degrees C for 30 h, and the best film showed a sharp superconducting transition at above 105 K. The low-Tc phase was formed in the partial melting process that is, sintering at 850 degrees C for 1 h and slowly cooling to 830 degrees C, and the low-Tc phase grains were highly textured. The film showed zero resistance at 75 K and the critical-current density of this film was about 2500 A cm-2 at 25 K.