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 oxides were prepared by calcination at 800 °C and firing at 855 °C. From X-ray powder diffraction analysis data, the ratio of low- and high-temperature phases was calculated. The material with the nominal composition Bi₂Pb_0.5Sr₂Ca_2.5Cu_3.5O _x was chosen for further experimental work. Samples fired at 800 °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=0) 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 °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.