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

非技术描述：磷镍超导体含有砷，这是元素周期表中的砷元素，是科学和技术上令人感兴趣的材料。它们在科学上很有趣，因为它们还含有铁，在发现橄榄石超导体之前，人们认为铁可以防止超导。它们在技术上很有趣，因为它们是极少数具有使其适合实际应用的特性的超导材料之一。对于实际应用来说，最重要的特性是超导体能够携带巨大的电流，并使这些电流在多晶圆线中穿过晶界。磷灰石超导体具有出人意料的大电流跨晶界传输，可以制成圆线，这是实际应用的首选形式。这项研究调查了控制电流通过晶界的因素，目的是进一步增加电流输运。用这些磷灰石超导体制成的导线可能有助于提高磁共振成像(MRI)系统的性能和降低操作成本，它们可能被用于解开蛋白质分子结构的超高场磁体。技术细节：这项研究调查了合成和掺杂在决定干净、连接良好的磷灰石超导体的未织构多晶的微结构和超导性能中所起的作用。通过改变引起超导电性的掺杂离子和改变加热制度来改变颗粒和晶界。测量了多晶样品的电磁性能，并用扫描和透射电子显微镜研究了晶界。这种稀土矿具有改变高场磁体技术的潜力，因为它们无织构的圆线形式远远好于高织构的氧化钇(YBCO)涂层导体，后者目前被视为高场磁体的突破技术。这项研究是由一名研究生和本科生共同完成的。暑假期间，有来自其他大学的K-12教师(NSF-RET)和暑期本科生(NSF-REU)进行相关的动手研究项目。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.