ORCID Profile
0000-0002-6497-5996
Current Organisation
University of Oxford
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Publisher: IOP Publishing
Date: 11-09-2018
Publisher: Oxford University Press (OUP)
Date: 31-01-2017
DOI: 10.1017/S1431927616012757
Abstract: The functional properties of the high-temperature superconductor Y 1 Ba 2 Cu 3 O 7− δ (Y-123) are closely correlated to the exact stoichiometry and oxygen content. Exceeding the critical value of 1 oxygen vacancy for every five unit cells ( δ .2, which translates to a 1.5 at% deviation from the nominal oxygen stoichiometry of Y 7.7 Ba 15.3 Cu 23 O 54− δ ) is sufficient to alter the superconducting properties. Stoichiometry at the nanometer scale, particularly of oxygen and other lighter elements, is extremely difficult to quantify in complex functional ceramics by most currently available analytical techniques. The present study is an analysis and optimization of the experimental conditions required to quantify the local nanoscale stoichiometry of single crystal yttrium barium copper oxide (YBCO) s les in three dimensions by atom probe tomography (APT). APT analysis required systematic exploration of a wide range of data acquisition and processing conditions to calibrate the measurements. Laser pulse energy, ion identification, and the choice of range widths were all found to influence composition measurements. The final composition obtained from melt-grown crystals with optimized superconducting properties was Y 7.9 Ba 10.4 Cu 24.4 O 57.2 .
Publisher: IOP Publishing
Date: 05-07-2021
Abstract: Bulk superconductors can act as trapped-field magnets with the potential to be used for many applications such as portable medical magnet systems and rotating machines. Maximising the trapped field, particularly for practical magnetisation techniques such as pulsed field magnetisation (PFM), still remains a challenge. PFM is a dynamic process in which the magnetic field is driven into a superconducting bulk over milliseconds. This flux motion causes heating and a complex interplay between the magnetic and thermal properties. In this work, the local flux density during PFM in a MgB 2 bulk superconductor has been studied. We find that improving the cooling architecture increases the flux trapping capabilities and alters the flux motion during PFM. These improvements lead to the largest trapped field (0.95 T) for a single MgB 2 bulk s le magnetised by a solenoidal pulsed field magnet. The findings illustrate the fundamental role bulk cooling plays during PFM.
Publisher: IOP Publishing
Date: 19-08-2022
Abstract: Bulk, single grain RE–Ba–Cu–O (where RE = rare earth or yttrium) [(RE)BCO] high temperature superconductors could potentially be used to generate stable magnetic fields for magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR). In these applications, however, the homogeneity of the magnetic field is of critical importance. As a result, the spatial distribution of critical current density, J c , within the bulk single grain and the effects of the magnetisation process, which are primary drivers of the uniformity of the achievable trapped magnetic field, are fundamental to assessing the performance of these technologically important materials. This paper reports the systematic measurement of the distribution of J c – B at 77 K over a vertical cross-section of a single grain along a facet line and through the seed crystal [(110)- F ] at 20 positions within a 20 mm diameter Gd–Ba–Cu–O s le in an attempt to understand and assess the distribution of J c along this microstructural feature. A comparison of the data within the whole vertical plane across the seed measured along the a or b direction within the [(100)- a ] plane shows that J c – B at 77 K at the facet line is more than 10% higher for applied fields between 0.2 T and 2.5 T. The effect of the J c – B relationship of the facet line on the overall trapped field measured in an in idual bulk s le was investigated by measuring the magnitudes of trapped fields and their contour maps for sections cut from four single grain s les of GdBCO–Ag at different sizes and shapes parallel to the ab -plane from the top to the bottom of the bulk s le. Based on the results reported here, we demonstrate a method to achieve more uniform trapped fields through an optimal arrangement of an assembly of sections of in idual GdBCO single grains.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Susannah Speller.