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

固态电解法（SSEM）对于高熔点过渡金属的净化特别有效，其中直流电流在温度低于熔点的热处理过程中通过样品，带正电荷或负电荷的杂质离子被直流电场从样品的主要部分移动到电极上。我们将这种方法应用于高t_c Bi（2223）超导体中产生高临界电流I_c。以共沉淀粉末为原料制备样品。它是由管和棒组成的Ag同轴圆柱形管填充。将复合材料锻压成直径为2.5 mm的材料，在830℃的空气中烧结100h，再锻压成直径为2.2 mm的材料。将银导线作为电极连接到管道上，在820-840℃的空气中再次烧结150h。在第二次烧结时，我们在烧结的最后阶段通过陶瓷部分提供直流电流（5-15A），持续10-30h。研究了样品的显微组织和临界电流I_c。我们用SSEM制备了大量样品，并研究了I_c值与显微组织的关系。经SSEM处理和不经SSEM处理的样品在微观结构因素上没有差异。然而，样本数量的I_c直方图显示，有SSEM的样本在I_c=15-20A附近出现峰值，而没有SSEM的样本随着I_c呈单调下降。这一事实表明，SSEM对于在Bi（2223）超导导线中再现远高于10 A的高I_c值是有效的。

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.