Preparation and Properties of Pb-Doped Bi-Sr-Ca-Cu-O Superconductors
Bi-Sr-Ca-Cu-O superconductors with a Pb addition were prepared by a conventional solid state reaction. Early in the sample heat treatment a large volume fraction of low-Tc phase (Bi2Sr2Ca1Cu2Ox) exists. With further sintering the volume fraction of the high-Tc phase (Bi2Sr2Ca2Cu3Ox) gradually increases. A zero resistance transition temperature of 110K was achieved for samples with a nominal composition of Bi0.7Pb0.3Sr1Ca1Cu1.8Ox and a sintering treatment of 845°C for 300 h in air. The critical current density, Jc, of the sample at 77K in zero magnetic field is 210 A/cm2, which is much larger than that of Pb-free sample. A pellet compaction process to densify and align the grains of high-T phase during an interrupted sintering treatment has been shown to be an effective method to increase Jc. A J greater than 1100 A/cm2 can be easily achieved by this process. A new mode of modulation with a wave length of about 50 A is seen in the Pb modified material in addition to the conventional modulation observed in the Pb-free system. Periodicities of the new, as well as, conventional modulation modes become less regular in the Pb-doped system.
KeywordsNominal Composition Critical Current Density Conventional Solid State Reaction Large Volume Fraction Conventional Modulation
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