Transmission EBSD (t-EBSD) as Tool to Investigate Nanostructures in Superconductors
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The transmission electron backscatter diffraction (t-EBSD) technique has proven to be an indispensable tool for the analysis of microstructures of superconducting samples, both high-Tc samples (YBa2Cu3Oy, Bi2Sr2CaCu2O8) as well as MgB2 or iron-based materials. The knowledge of the grain boundary properties (misorientation, length, width) is essential for the further optimization of sample performance. Any addition of secondary phase(s) to improve the flux pinning properties is required to be of nanometer dimensions, so the higher achievable resolution and the better imaging properties are important to obtain reasonably high image quality to enable automated orientation mapping. The orientation maps reveal not only the location and the shape of the inclusions within the superconducting matrix or at the grain boundaries but also their influence on the surrounding superconducting matrix, which also plays an important role in flux pinning. In the case of sintered MgB2 bulk samples, the demand for higher critical current densities leads to MgB2 grains in the 100-nm range, which is already difficult to be studied by means of conventional EBSD. Furthermore, t-EBSD is useful for the analysis of specific microstructures of unconventional superconductors like superconducting foams or superconducting nanowire networks.
KeywordsSuperconductors Transmission electron backscatter diffraction Nanometer-sized grains Pinning centers Orientation mapping
We thank J. Noudem (CRISMAT, Caen, France) for providing us with the spark-plasma sintered MgB2 sample, K. Nakazato, M. Muralidhar (SIT, Tokyo, Japan) for the IG-processed YBCO bulk, and X. L. Zeng (Saarland University, Saarbrücken, Germany) for the Bi-2212 nanowire fabrics and K. Berger, B. Douine (GREEN, Nancy, France) for valuable discussions. This work is part of the SUPERFOAM international project funded by ANR and DFG under the references ANR-17-CE05-0030 and DFG-ANR Ko2323-10, respectively.
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