Development of new oxide superconductors for materials of the MRI magnet wire

在高温下表现出超导电性的新材料一直是人们热切期望的。它们是有用的材料，核磁共振磁铁的导线。我们对合成与材料相适应的新型超导氧化物进行了基础性研究。我们的研究成果总结如下：我们寻找了属于Ru基氧化物超导体的新材料，因为它们具有高T_c超导电性，而不需要像高压O_2气氛下热处理这样的空穴掺杂处理。因此，我们首次成功地合成了Ru-Sr-Ln(Ce)-Cu-O(Ln=Sm，Eu和Gd)系中具有超导和铁磁性的1232相。有趣的是，T_c值随着晶格参数的减小而增大，当Ln=Gd时，T_c值达到最大值。这一结果可以预期，T_c值与晶格参数相关。从这个期望中，我们执行…进一步进行了Ln=Gd的Ru基1232样品中Nb部分替代Ru的实验。Nb的离子半径大于Ru的离子半径。然后，我们得到了这样的实验结果：随着Nb取代量的增加，晶格参数增加，T_c值降低。然后，我们制备了许多用Sm、Dy和Ho部分取代Gd的样品。结果发现，当选择离子半径较小的Dy或Ho作为替代元素时，T_c值增大。这是我们获得的一个重要的实验事实，它表明含有CuO_2金字塔的钙钛矿型块体与晶体结构中存在的萤石型块体之间的失配引起的应力对T_c值有影响。此外，我们还成功地合成了新的Bi基2212相超导体。由于Bi^&lt；3+&gt；，Sr^&lt；2+&gt；和La^&lt；3+&gt；的离子半径相近，因此在Bi一sr-La-CuO系中从未合成过Bi2212化合物。这也是我们获得的重要实验结果之一，它表明我们设想的材料可以通过控制组成元素的离子半径来实现。较少

New materials showing superconductivity at high temperatures have been earnestly desired. They are useful as materials of the wire of the MRI magnet. We have made fundamental researches on synthesis of new superconducting oxides being agreeable to the materials. We show summary of the research results below.We had searched new materials belonging to the Ru-based oxide superconductors, because of their useful nature showing high-T_c superconductivity without such any treatment for hole-doping as annealing under high-pressure O_2 atmosphere. As a result, we succeeded for the first time in synthesis of the 1232 phase showing superconductivity and ferromagnetism in the Ru-Sr-Ln(Ce)-Cu-O system (Ln=Sm, Eu and Gd). Interestingly, he T_c values are increasing as the lattice parameters are becoming small, and the value comes to the maximum one in the case of the sample with Ln=Gd. This result can be expected that the T_c values correlate the lattice parameters. From this expectation, we perfor … More med an experiment of partial substitution of Nb for Ru in the Ru-based 1232 sample with Ln=Gd. Ionic radius of Nb is bigger than that of Ru. Then, we obtained such an experimental result that with increasing of the substituted quantity of Nb, the lattice parameters were increasing, the T_c values were expectedly decreasing. Then, we prepared many samples partially substituted for Gd by Sm, Dy and Ho. As a result, we discovered that the T_c values were increasing, when Dy or Ho with smaller ionic radius were selected for a substituted element. This is one of important experimental facts obtained by us, it suggests that the stress due to the mismatches between the perovskite-type blocks containing the CuO_2 pyramids and the fluorite-type ones existing in the crystal structure affects on the T_c values.Moreover, we have also succeeded in synthesizing new Bi-based superconductor of the 2212 phase by partial substitution of Pb for Sr and/or Bi in the Bi-Sr-La-Cu-O system. The Bi-2212 compound has never been synthesized in the Bi-Sr-La-Cu-O system because of similar values of the ionic radii of Bi^<3+>, Sr^<2+> and La^<3+>. This is also one of important experimental results obtained by us, it shows that our supposed materials can be realized by controlling the ionic radius of the constituent elements. Less