Improvement of the Transport Properties in BiSrCaCuO Superconductors prepared by Melt-Casting Process and Development of Bi-2212 HTS Current Leads

采用熔铸工艺(MCP)制备了含适量硫酸锶的Bi2212块体超导体。77K时，块体Bi2212bar(φ10.7 mm)的临界电流超过50A。在MCP示例中，薄弱环节已基本消除。输运性能的提高是由于碳酸锂(Li_2CO_3)的加入所致。在800℃下热处理的MCP样品Bi2Sr2CaCu2Li&lt；0.2&gt；Oy出现最高临界温度，并研究了MCP样品的交流输运损耗和临界电流密度分布。交流损耗主要归因于超导体的磁滞损耗。交流损耗值约为诺里斯理论理论值的一半。与均匀J_c分布的计算结果相比，样品从表面到内部的局部J_c值显著减小，抑制了交流电流传输下磁通穿透区向内部的扩展，降低了损耗的产生。目前的MCP Bi-2212大块超导体似乎很有希望作为电流引线。

The Bi-2212 bulk superconductors, with a proper amount of SrSO_4, were prepared by melt-casting process (MCP). Critical current in bulk Bi2212 bar (φ10.7mm) exceeded 50A at 77K. The weak links have been largely eliminated in the MCP sample. The enhancement of transport properties is due to the addition of lithium carbonate (Li_2CO_3). The maximum critical temperature occurs for the MCP sample Bi_2Sr_2CaCu_2Li_<0.2>O_y annealed at 800°C. And, we have investigated the ac transport losses and critical current density distribution of MCP samples. The ac losses are mainly ascribed the hysteresis loss of the superconductor. The ac loss value is about one-half of the theoretical value obtained by the theory of Norris. The local J_c value decreases significantly in going from the surface to the interior of the sample, which suppresses the extension of the flux-penetration-region to the interior under ac current transmission and lowers the loss generation compared with the calculated results obtained by the uniform J_c distribution. Present MCP Bi-2212 bulk superconductors seem to be promising as a current lead.