Abstract:

The bulk superconductors with the nominal composition Bi_xPb_ySr₂Ca_1.7Mg_0.3Cu_zO_w(x=1.92, 1.90, 1.87, y = 0.32, 0.315, 0.31, 2 = 3.11, 3.07) are synthesized by solid state reaction. Resistivity and AC susceptibility measurements demonstrate the values of superconducting critical temperature Tc of six kinds of compounds sintered at seven different temperature. The highest zero resistivity temperature Tc(ρ = 0) is 105.8K. x-ray powder diffraction patterns and AC susceptibility measurements show that the volumetric ratio of 110K phase to 80K phase increases with sintering temperature in the range of 833.0℃ to 843.3℃. The break morphology of the sample is studied by SEM. The results of DEAX display that the residual amounts of Pb and Bi in the sample, which have influence on the growth process of 110K phase, are controlled by sintering temperature and time, DTA curves indicate that the lowering of the partial melting temperature caused by the addition of Mg element results in the formation of superconducting phase in Bi Pb Sr Ca Mg Cu O system at lower sintering temperature.

Key words: superconductor, solid state reaction, Bi system compound