Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.686173
Title: Control of crystallisation in the yttrium barium copper oxide system
Author: Boston, Rebecca Helen
ISNI:       0000 0004 5918 0253
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Abstract:
The control of crystallisation of complex oxides on the nano- and macro-scale is vital for the progression of technology and the fundamental understanding of the processes which govern functional oxide synthesis. The use of biotemplates has been shown to be a highly effective means of controlling both the phase and morphology of complex oxides, with macro- and nano-structures being formed which would otherwise be impossible using standard synthetic techniques. One complex functional material, yttrium barium copper oxide (YBCO), has generated huge amounts of interest for its superconducting properties, in particular its relatively high transition temperature (93 K), however given the complex nature of its crystal structure, it has proved to be very difficult to illicit control over the crystallite growth on the nano- or larger scales. Standard synthetic techniques, whilst very effective in producing a pure phase, are either slow or prohibitively expensive, and, due to the processes involved, offer no control over the final morphology. Herein are presented several new methods for the production of superconducting YBCO, including macro-scale control of polycrystalline samples in the formation of hollow microspheres through the use of the polysaccharide dextran, monolithic foams and highly layered tapes using a graphene oxide template, and nano-scale control to produce nanowires, through which a type of nanowire growth, the microcrucible mechanism, which has been directly observed and characterised for the first time. In addition, two sulphur-containing templates, K-carrageenan and a barnacle cement protein, which were thought to be unsuitable for use with YBCO (and any other phases containing precursors which would form stable sulphates during synthesis) were also investigated and found, after careful optimisation of the synthesis protocol, to be useable under certain experimental constraints. This is significant as it means that sulphur-rich proteins can now be successfully used for the production of YBCO, with the possibility of creating designer morphologies, giving even higher control over crystallisation. Each templating protocol was fully investigated using the standard chemical and physical characterisation techniques such as powder X-ray diffraction and transmission electron microscopy, in order to examine the phases and morphologies produced, and the superconducting properties investigated using a superconducting quantum interference device magnetometer. Where appropriate a number of other techniques such as in situ measurements using heating stages or X-ray micro computer-aided tomography were employed to give a deeper understanding of each templated system. The templating systems detailed here for YBCO should be applicable for other complex oxides, with the insights gained into the mechanisms which govern the phases and morphologies formed allowing optimised systems to be more quickly developed. This may lead to further advances in the production of complex functional oxide materials
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.686173  DOI: Not available
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