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Title: Fabrication and characterisation of joins in melt-textured YBa₂Cu₃O₇-δ
Author: Bradley, Alistair David
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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The development of bulk superconductors for engineering applications, where large critical current densities (Jc's) must be supported over large areas and at relatively high fields and temperatures, is one of the key issues in current superconductivity research. Melt-textured YBa2Cu2O7-δ (YBCO) offers the greatest potential for such applications, however the limited size of single grains which can be grown and the limited Jc supported by grain boundaries (GBs) have presented major hurdles. This thesis describes the fabrication of joins between YBCO grains, which opens up the possibility of producing larger samples of any shape and orientation. The joining technique uses a barium-cuprate 'liquid phase' released from the grains themselves above 920°C to mediate the epitaxial growth of YBCO across the interface between two grains. The microstructure and composition of joins fabricated with different orientations were investigated using optical, transmission electron and secondary electron microscopy. Extensive electrical measurements were made in order to determine the electromagnetic properties of the joins. Measurement of resistance as a function of temperature revealed information about the GB formed at the join. The maximum field dependent temperatures at which a Jc could be supported by different joins was determined (the 'irreversibility line') and compared directly with that of the adjoining grain material. The results have shown that joins with well defined GBs are formed, generally behaving like those found in other bulk and thin-film YBCO samples. Further optimisation of the joining technique is required, however great promise is shown for scale-up of the process to produce samples suitable for engineering applications.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available