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

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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.