MELT PROCESSING OF YBaCuO SUPERCONDUCTORS AND CRITICAL CURRENTS
MELT PROCESSING OF YBaCuO SUPERCONDUCTORS AND CRITICAL CURRENTS
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YBaCuO 超导体的熔融加工和临界电流
DOI：
10.1142/s0217984990000234
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发表时间：
1990
影响因子：
1.9
通讯作者：
M. Murakami
中科院分区：
文献类型：
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作者：
M. Murakami
在Y-Ba-Cu-O系中，超导相是由包晶反应产生的：Y2BaCuO5(211)+L→2YBa2Cu3Ox(123)。为了促进123相的连续生长，需要在液中均匀分布211相。在这篇综述中，我首先介绍了熔融过程，它使我们能够在液体中实现211的精细分散。通过在温度梯度中缓慢冷却，可以从这种前驱体结构中生长出大尺寸的123晶体。由于包晶反应不完全，晶体中含有细小的211包裹体。211夹杂物在123基体中的细小弥散被认为有三个有益的作用：1)抑制裂纹的形成；2)促进氧的扩散；3)提供钉扎中心。根据输运和磁性测量，这种晶体在77K和1T时表现出超过104A/cm2的大Jc值。磁化强度测量还表明，在样品中建立了临界态模型，表明不存在弱连接。与单晶相比，磁通蠕变速率相当小。根据传统的磁通钉扎理论估算了211夹杂物可获得的JC。最后，提出了这种晶体作为超导永磁体的应用。
In the Y–Ba–Cu–O system, the superconducting phase is produced by a peritectic reaction: Y2BaCuO5(211) + L → 2YBa2Cu3Ox (123). In order to promote the continuous growth of the 123 phase, uniform distribution of 211 in the liquid is required. In this review, I first present the melt process which enables us to achieve fine dispersion of 211 in the liquid. Large 123 crystals can be grown from this precursor structure by slow cooling in temperature gradient. As a result of incomplete peritectic reaction, the crystals contain fine 211 inclusions. The fine dispersion of 211 inclusions in the 123 matrix is considered to have three beneficial effects: 1) to suppress crack formation; 2) to promote oxygen diffusion; and 3) to provide pinning centers. Such crystals exhibit large Jc values exceeding 104A/cm2 at 77 K and 1 T according to both transport and magnetic measurements. Magnetization measurements also show that the critical state model is established in the sample indicating that no weak-link is present. Flux creep rate is reasonably small compared to that of single crystals. Attainable Jc due to the 211 inclusions is estimated based on the conventional flux pinning theory. Finally, I propose the application of such crystals as a superconducting permanent magnet.