SYNTHESIS AND ANALYSIS OF PBO-MODIFIED BI-SR-CA-CU-O SUPERCONDUCTORS

High T-c superconducting materials based on a PbO-modified Bi-Sr-Ca-Cu-O system with various ratios between the prides were prepared by calcination at 800 degrees C and firing at 855 degrees C. From X-ray powder diffraction analysis data, the ratio of low- and high-temperature phases was calculated. The material with the nominal composition Bi2Pb0.5Sr2Ca2.5Cu3.5Ox was chosen for further experimental work. Samples fired at 800 degrees C contain mostly the low-temperature phase (2212). Higher firing temperatures lead to the formation of the high T-c phase (2223) with T-c (R = O) over 100 K. Some samples were cold pressed and refired which increased the specific density to over 80% of the theoretical density. The composition of samples was investigated by X-ray powder diffraction analysis and by energy dispersive X-ray spectroscopy. The main phase in the material fired at 800 degrees C, is the low T-c phase 2212, and secondary phases are Ca2PbO4, unreacted CuO and traces of 2223 phase. At higher firing temperatures, the main phase is the high-temperature phase 2223. The material is still heterogeneous and contains Ca2PbO4.