CRYSTALLIZATION PROCESS AND SUPERCONDUCTING PROPERTIES OF BI-PB-SR-CA-CU-O THICK-FILMS CRYSTALLIZED FROM AN AMORPHOUS STATE

We have studied the crystallization process in the Bi-Pb-Sr-Ca-Cu-O system from an amorphous state, and we have characterized the superconducting properties of thick film samples prepared on MgO substrates by annealing. A rapidly quenched sample showed amorphous nature. After this sample was annealed at 500 degrees C, Bi2Sr2CuOx phase was found. At 650 degrees C, the Bi2Sr2CaCu2Oy phase appeared. The sample at 800 degrees C consisted of the Bi2Sr2CaCu2Oy phase, while the Bi2Sr2Ca2Cu3Oz phase occurred at 850 degrees C. Thick film samples were prepared by annealing at 855 degrees C, the partial melting temperature, for 1-400 h. A short-time annealed sample showed semiconducting behavior in the normal conducting state, but longer annealing showed the more remarkable metal-superconducting transition. This was considered to be due to oxygen deficiency and weak coupling at grain boundaries. The highest T-c(O) is 91K in a sample annealed for 400 h., although it consisted of high-T-c and low-T-c mixed phases.