Superconducting materials exhibit effects which can be used to improve a wide range of existing technologies, and enable the creation of entirely new ones. The infinite conductivity of superconductors results in high specific power and efficiency, making them an attractive replacement for conventional conductors. By far the most technologically useful material is Yttrium Barium Copper Oxide (YBCO), which superconducts well above the temperature of cheap, readily available liquid nitrogen (77K), which makes cooling it to the required temperature economically viable. Improvement of flux pinning and thus the critical current, <i>J<sub>c</sub></i>, that can be carried in YBCO is crucial for achieving widespread applications of this technologically important material. This thesis presents an investigation into pinning in thin films of YBCO, via inclusions of a non-superconducting stable oxide phase, RE<sub>3</sub>TaO<sub>7</sub>, where RE = Sm, Gd, Er or Yb. This second phase provides both ideally sized <i>c</i> axis correlated and random pinning sites and results in an order of magnitude improvement of critical current over pure YBCO at 1 Telsa. Additionally, RE<sub>3</sub>TaO<sub>7</sub> does not depress the superconducting transition temperature, as has been found with the closest performing additives based on BaWO<sub>3</sub>, where W = Zr or Sn. The thin films studied were grown by pulsed laser deposition and characterised with a standard four point measurement technique, transmission electron microscopy, X-ray diffraction, atomic force microscopy and X-ray Photoelectron Spectroscopy. Additionally, the importance of surface pinning in doped films was investigated and the mixing of the second phase with YBCO during the initial layers of film growth was found to have a large effect of the pinning at that interface.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:603737 |
| Date | January 2009 |
| Creators | Harrington, Sophie-Ann |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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