Atom Probe Tomography analysis of BaFe2As2 superconductors for high field applications

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This project will form part of a collaboration between Oxford and the Applied Superconductivity Center in Florida (https://nationalmaglab.org/). The context of the research is that there is a strong international effort to select superconducting materials for the magnets needed for large physics machines like the Future Circular Collider at CERN. The target values for current carrying capacity of the superconducting windings are extremely demanding, Jc = 1500 A/mm2 at 4.2 K in 16 T, and rather few classes of superconducting material can possibly achieve this value. One of materials being explored for this and similar high-field applications is the class of materials based on the compound BaFe2As2 (122) which can be made from inexpensive starting raw materials, and at least in single crystals possesses the superconducting properties needed for high-field magnet applications. However the processes used to manufacture the multi-filamentary conductors needed for magnets results in polycrystalline 122 filaments with substantially degraded properties, and the major manufacturing challenge at the present time is improving the processing to increase current flow across grain boundaries. The most important technological questions are what degrades the GB connectivity in 122, how this degradation can be avoided, and is this solution applicable in an affordable manufacturing process? Recent studies suggest that the GB connectivity in state-of-the-art 122 polycrystals is degraded primarily by impurities at the grain boundaries, and so correlating the nano-scale chemistry with the manufacturing route and superconducting performance is the key focus of international research in this area.Our project partner in the USA, Prof. Fumitake Kametani of Florida State University is an expert in the synthesis and performance of this class of superconductor. He has recently received funding from the DoE to study the manufacturing of 122 materials under ultra-clean conditions. This project will use Atom Probe Tomography as the primary technique to analyse the local chemistry of grain boundaries in a unique set of 122 samples prepared under these carefully controlled conditions. APT is the only technique that offers very high resolution 3D analysis of chemical distributions in grain boundaries in microstructures with nanometer grain sizes, and the student will have the opportunity to become an expert user of one of the most versatile high resolution analysis techniques and become a member of the team exploring practical ways to improve the performance of one of the most promising new classes of superconducting compounds.This project spans key topics in the EPSRC Energy Theme (Materials for Energy, Manufacturing Technology) and the Engineering Theme (Manufacturing Technology, Materials Engineering, Engineering Design).