Understanding the Role of Grain Boundaries in Limiting the Critical Current Density of Pnictide Superconductors

非技术描述：镍超导体含有元素周期表中的一种元素砷，在科学和技术上都是有趣的材料。它们在科学上很有趣，因为它们还含有铁，而铁在镍超导体被发现之前，被认为会阻止超导性。它们在技术上很有趣，因为它们是为数不多的具有适合实际应用的特性的超导材料之一。在实际应用中，超导体最重要的特性是能够携带大量电流，并使这些电流在多晶圆线中跨越晶界。pnictide超导体具有意想不到的高电流跨晶界输运，它们可以制成圆线，这是实际应用的首选形式。本研究旨在进一步研究控制电流跨晶界输运的因素。用这些pnictide超导体制成的导线可能有助于提高磁共振成像（MRI）系统的性能并降低操作成本，它们可能用于用于解开蛋白质分子结构的超高场磁体。技术细节：本研究探讨了合成和掺杂在确定干净、连接良好的镍基超导体的无织构多晶的微观结构和超导性能方面所起的作用。通过改变诱导超导的掺杂离子和改变加热时间来改变晶粒和晶界。用扫描电镜和透射电镜研究了多晶样品的电磁性能和晶界。这种化合物具有改变高场磁体技术的潜力，因为它们的无纹理、圆线形式远远优于高度纹理的钇钡铜氧化物（YBCO）涂层导体，后者目前被视为高场磁体的突破技术。本研究由一名研究生和一名本科生共同完成。在夏季，有K-12教师（NSF-RET）和来自其他大学的暑期本科生（NSF-REU）做相关的实践研究项目。这项工作与美国、欧洲、亚洲和澳大利亚的研究小组进行了富有成效的合作。

NONTECHNICAL DESCRIPTION: Pnictide superconductors, which contain arsenic, one of the pnictogen elements in the periodic table, are scientifically and technically interesting materials. They are scientifically interesting because they also contain iron, which, until the pnictide superconductors were discovered, was thought to prevent superconductivity. They are technically interesting because they are one of the very few superconducting materials that have properties that may make them suitable for practical applications. The most important property for practical applications is the ability for the superconductor to carry enormous amounts of current and for this current to go across grain boundaries in polycrystalline round wires. The pnictide superconductors have unexpectedly high current transport across grain boundaries and they can be made as round wires, which is the preferred form for practical applications. This research investigates the factors that control current transport across grain boundaries with the goal of increasing it even further. Wires made with these pnictide superconductors may help improve the performance and decrease the operating cost of magnetic resonance imaging (MRI) systems and they may be used in very-high field magnets that are used to unravel the structure of protein molecules.TECHNICAL DETAILS: This research investigates the role that synthesis and doping play in determining the microstructural and superconducting properties of untextured polycrystals of clean, well-connected pnictide superconductors. The grains and grain boundaries are modified by changing the dopant ions that induce superconductivity and varying the heating schedules. The electromagnetic properties of the polycrystalline samples are measured and the grain boundaries are investigated using scanning and transmission electron microscopy. The pnictides have the potential to transform high-field magnet technology because their untextured, round-wire form is far preferable to the highly-textured yttrium barium copper oxide (YBCO) coated conductors that are currently seen as the breakout technology for high-field magnets. This research is done by a graduate student and undergraduate students. During the summers there are K-12 teachers (NSF-RET) and summer undergraduate students from other universities (NSF-REU) who do relevant, hands-on research projects. This work has productive collaborations with research groups in the US, Europe, Asia, and Australia.