Abstract
Superconducting single-grain YBCO bulk samples with the ability to trap high magnetic fields can be grown using the top-seeded melt-growth process. Multiseeding techniques have the potential to enable larger diameter bulks to be grown, but the performance of these materials is not yet comparable to the single-seeded bulks. Here we carry out detailed three-dimensional microstructural characterisation on a multiseeded sample grown with the seeds aligned in the 0°–0° geometry using high resolution microanalysis techniques. Chemical and structural variations have been correlated with the trapped field distribution in three separate slices of the sample. The top slice of the sample shows four peaks in trapped field, indicating that the current flows in four separate loops rather than in one large loop within the sample. This has been explained by the build-up in insulating Y-211 particles where the growth fronts from the two seeds meet, forming a barrier to current flow, as well as the low Y-211 content (and hence low Jc) of the large c-axis growth sector.
Highlights
The extraordinary ability of single grain bulk (RE)BaCuO (RE = rare Earth element) high temperature superconductors (HTS) to trap magnetic fields over 17 T at 26 K [1] leads to their potential application in practical devices including stable levitation [2] and flywheel energy storage devices using superconducting bearings [3, 4]
The bulk crystal grows from the seed in five growth sectors; 4 a-axis growth sectors (a-GS) grow laterally outwards from the seed crystal in the a-axis direction and a c-axis growth sector (c-GS) extends downwards from directly beneath the seed, spreading out laterally in a square pyramid shape as it grows
This paper describes the first time that detailed three-dimensional microstructural characterisation, using a combination of high resolution EDX and Electron backscatter diffraction (EBSD) techniques, has been correlated with the trapped magnetic field performance of slices of top-seeded melt growth (TSMG) YBCO bulk
Summary
In the TSMG process, slow growth rates are required to control the nucleation of the bulk and allow the peritectic formation of the superconducting (RE)Ba2Cu3O7 phase, limiting the practical sample size that can be fabricated from a single nucleation point [7, 8]. A variety of seed arrangements have been studied, generally exhibiting rather inconsistent trapped field values attributed the presence of a grain boundary or residual liquid phase where the growth fronts meet [9, 10, 12, 13]. We present a detailed examination of the microstructural development of a 0°–0° multi-seeded bulk YBaCuO sample and compare the microstructure with trapped field for the same sample to enable the origin of the poor performance of these multiseeded bulks to be confirmed
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