Microstructure and critical current density in Bi(2223) superconductors prepared by solid-state electrolysis method

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Solid-state electrolysis method (SSEM) is effective particularly for purification of transition-metals with high melting points, where a DC current is passed through the sample during heat treatments at temperatures just below the melting point and impurity ions with positive or negative charges are moved away from the main part of the sample to the electrodes by the DC electric field. We applied this method for producing high critical currents I_c in high-T_c Bi(2223) superconductors.The co-precipitation powder was used as the starting material for sample preparation. It was packed with Ag coaxial cylindrical tubes consisting of the pipe and rod. The composite was swaged into 2.5 mm in diameter and sintered at 830 ﾟC in air for 100h and re-swaged into 2.2 mm in diameter. After Ag leads were attached to the pipe as electrodes, the sample was sintered again at 820-840ﾟC in air for 150h. During second sintering, we supplied DC current (5-15A) through ceramics part for 10-30h at the last stage of this sintering. The microstructure and critical current I_c of the samples were investigated.We prepared a large number of the samples with SSEM, and investigated the relation between the microstructures and the I_c values. There is no difference in microstructural factors between the samples with and without SSEM.However, the I_c histogram for the sample number shows that the sample with SSEM exhibits a peak around I_c=15-20A, while the sample without SSEM shows a monotonic decrease with I_c. This fact shows that the SSEM is effective for reproducing high I_c values well above 10 A in the Bi(2223) superconducting wires.