Abstract
The melt processing of Y–Ba–Cu−O (YBCO) single grains has been investigated using different isothermal temperature profiles for precursor powders containing varying amounts of Y-211. The crystal morphology of the as-grown YBCO single grains and the growth rate, which is influenced critically by the initial Y-211 content and the under-cooling temperature, have been analyzed. A simple method to determine an optimum temperature profile for the growth of bulk YBCO single grains has been proposed based on the results of this investigation. The influence of the initial Y-211 content on the macrosegregation of Y-211 inclusions for the different crystallographic orientations and different under-cooling temperatures has been analyzed. The correlation between the initial Y-211 content and the macrosegregation of Y-211 inclusions within the YBCO single grain along the different growth directions is interpreted from the growth rate data using Y-diffusion mechanism and pushing/trapping theory. Finally, an improved method for fabricating bulk YBCO superconductors containing a uniform distribution of pinning centers in the single grain, which has significant potential for improving the superconducting properties of bulk YBCO superconductors for practical applications, is proposed.
Highlights
Bulk Y−Ba−Cu−O (YBCO) superconductors have significant potential for high field, permanent magnet applications[1] such as flywheel energy storage systems[2] and magnetic bearings[3] because of their ability to trap large magnetic fields at the boiling point of liquid nitrogen (77 K).[4]
The shift of the peak position of the temperature curves represents that the kinetic of the peritectic decomposition temperature of the precursor powders decreases as the Y-211 content increases, as indicated by the dashed line in Figure 4, panel a
YBCO samples containing different weight amounts (20, 30, and 40 wt %) of Y-211 were grown in batches by top seeded melt growth using different, isothermal temperature profiles
Summary
Bulk Y−Ba−Cu−O (YBCO) superconductors have significant potential for high field, permanent magnet applications[1] such as flywheel energy storage systems[2] and magnetic bearings[3] because of their ability to trap large magnetic fields at the boiling point of liquid nitrogen (77 K).[4]. The Y-123 single grain nucleates epitaxially from a seed, which has a higher melting temperature and a similar crystal structure to the Y-123 phase, as the temperature is decreased below the peritectic solidification temperature (Ts) on cooling, as described by the following reaction:[5]
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