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Controlling the Critical Current Density under Magnetic Field of Melt Processed Bulk High Temperature Superconductors

熔融加工块体高温超导体磁场下临界电流密度的控制

基本信息

批准号：
14350006
负责人：
IKUTA Hiroshi
金额：
$ 7.3万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

The change of the critical current density (J_c) as well as the trapped field of melt-processed bulk superconductors brought about by an element substitution, oxygen annealing, changing the composition of the starting materials and so on were systematically studied. First, we optimized the starting composition of the Dy-system. Then, CeO_2 was added, which decreased the loss of the melt during the processing, resulting in a more than 10% increase in the trapped field. The addition of ZnO to this composition increased J_c between 0 and 3 T, and the trapped field increased for 20%. The optimum content of ZnO for increasing J_c and the trapped field was determined to be about 0.025 wt.% independent of the sample size and regardless whether CeO_2 is added or not. When ZnO was added to the Sm-system, the trapped field increased by a factor of 1.5. It was elucidated that the increase in J_c with Zn doping is particularly large in the region beneath the seed crystal where the Sm211 phase is d … More eficient, and this brought about the increase of the trapped field. We have also succeeded for the first time the preparation of single-domain bulk samples of the ternary Nd-Eu-Gd system with a diameter equal to or larger than 30 mm. The trapped field of these samples was larger when the ratio of Gd in the 211 phase of the starting materials was smaller, but the material strength increased when the content of Gd was large. Consequently, the magnetic flux density that the sample could trap without being cracked at low temperature increased. Similarly, the trapped field at the liquid nitrogen temperature of the ternary Sm-Eu-Gd system was large when the content of Gd of the 211 phase was 50%. The diffusivity of oxygen in a melt-processed superconductor was found to be between single-and poly-crystalline samples, and decreases when Ag is added because the microstructure is denser. It was important to perform the oxygen annealing at low temperature for the Sm-system in order to obtain a sample with large J_c and trapped field. However, the diffusivity decreases at lower temperature, and therefore, we studied the effect of high pressure oxygen annealing under 10 atm. Based on that result, we proposed a two-step annealing process, and confirmed its effectiveness. We also prepared samples of the Sm-system with adding Y_2Ba_4CuZrO_y, which was reported to have a small size in melt-processed superconductors, and found that the addition of this material compensates the Sm211 phase that is deficient under the seed crystal, and the trapped field increased with a very small content of about 1mol%. Less

本文系统地研究了元素替代、氧退火、改变原料成分等因素对熔体加工块状超导体临界电流密度（J_c）和俘获场的影响。首先，我们优化了Dy-体系的起始组成。然后加入CeO_2，减少了熔体在加工过程中的损耗，使俘获场增加了10%以上。在0 ~ 3 T范围内，ZnO的加入提高了J_c，陷阱场提高了20%。ZnO的最佳含量为0.025wt.%左右，有利于提高J_c和陷阱场与样品大小无关，也与是否加入CeO_2无关。当ZnO被添加到Sm-系统中时，捕获场增加了1.5倍。结果表明，Zn掺杂使晶种下Sm_（211）相为d_（211）相的区域的J_c增加得特别大 ...更多信息效率高，这带来了被困场的增加。我们还首次成功地制备了直径大于等于30 mm的Nd-Eu-Gd三元系单畴体样品，当Gd在起始材料211相中的比例较小时，这些样品的俘获场较大，但当Gd含量较大时，材料强度增加。因此，在低温下样品可以捕获而不破裂的磁通量密度增加。同样，当211相Gd含量为50%时，Sm-Eu-Gd三元系在液氮温度下的陷阱场较大。氧在熔融处理的超导体中的扩散率介于单晶和多晶样品之间，并且当添加Ag时由于微观结构更致密而降低。为了获得大的J_c和陷阱场，对Sm-系统进行低温氧退火是很重要的。然而，在较低的温度下，扩散率降低，因此，我们研究了10大气压下的高压氧退火的效果。在此基础上，提出了两步退火工艺，并验证了其有效性。我们还在Sm系样品中加入了Y_2Ba_4CuZrO_y，发现这种材料的加入弥补了籽晶下缺少的Sm_（211）相，并且在很小的含量（约1mol%）下，俘获场增加。少