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

系统地研究了元素替代、氧退火、改变起始材料成分等引起的熔融加工块体超导体的临界电流密度（J_c）和俘获场的变化。然后，添加了CeO_2，这减少了加工过程中熔体的损失，导致俘获场增加了10%以上。在该组合物中添加ZnO增加了J_c。 0和3 T，并且捕获场增加了20%，用于增加J_c和捕获场的最佳ZnO含量被确定为大约0.025wt.%，与样品尺寸无关并且无论是否添加CeO_2。 ZnO 被添加到 Sm 系统中，俘获场增加了 1.5 倍，结果表明，Zn 掺杂后 J_c 的增加在 Sm 系统下方的区域特别大。我们还首次成功制备了三元 Nd-Eu-Gd 体系的单畴块状样品。当原材料211相中Gd的比例较小时，这些样品的捕获场较大，但当Gd含量较大时，材料强度增加。同样，当211相Gd含量为50%时，三元Sm-Eu-Gd体系在液氮温度下的俘获磁场较大。研究发现，熔融加工的超导体中氧的扩散率介于单晶和多晶样品之间，并且当添加 Ag 时，氧的扩散率会降低，因为微观结构更致密，因此氧的扩散很重要。对Sm体系进行低温退火以获得大J_c和俘获场的样品，但在较低温度下扩散率会降低，因此我们在此基础上研究了10 atm下的高压氧气退火的效果。结果，我们提出了两步退火工艺，并证实了其有效性。我们还制备了添加 Y_2Ba_4CuZrO_y 的 Sm 体系样品，据报道其尺寸较小。研究人员对熔融加工的超导体进行了研究，发现该材料的添加弥补了籽晶下方不足的Sm211相，并且俘获场以约1mol%的极小含量增加。