The structure and electric properties of thallium-based superconductors
The structure and electric properties of thallium-based superconductors
Comprehensive studies of the synthesis conditions for preparing thallium cuprate superconductors in bulk quantities have been carried out. The n= 2, 3 and 4 members of the homologous series Tl2Ba2Ca(n-1)CunO2n+4 havebeen prepared by reaction of the component oxides and precursors and the optimum preparative conditions for the reproducible synthesis of these materials have been identified. The formation and superconducting properties of these phases were found to be strongly dependent upon the nominal composition and synthetic environment. The effect of various parameters such as reaction temperature, time, precursor, composition and atmosphere on phase formation and Tc were ascertained. Starting stoichiometries of x= 0, 0.2 and 0.5 in the series Tl2-xBa2Ca(n-1+x)CunO2n+4were required for the formation of bulk phase material corresponding to n= 2, 3 and 4 respectively. The optimum conditions of synthesis were identified as; 890oC for 6 hours in oxygen (for n= 2), 890oC for 6 hours in oxygen (for n= 3), and 860oC for 10 hours in air (for n= 4), each followed by a slow cool to room temperature to ensure an even distribution of oxygen throughout the material. Annealing in atmospheres of argon and oxygen (up to pressures of 500 atm.) was found to induce changes in Tc in the c lattice parameter.
Detailed powder neutron diffraction studies were carried out at the HRPD facility, ISIS on 2212 and 2223 and revealed that the crystal sturctures were very sensitive to slight changes in the oxygen content. The a lattice parameter was found to be about 3.85AA in all materials and was almost invariant to changes in the oxygen content as a result of the in-plane rigidity of the Cu-O bonds. However, the c parameter, at 29.3AA for n= 2, 35.6AA for n = 3 and 42.0AA for n = 4, was found in each to decrease with increasing oxygen content. In the TI-O portion of the structure thallium was found to reside in a strongly distorted octahedron with two short apical bonds of typically 2.0AA, and two moderate and two long bonds in the a-b-plane at 2.4AA and 3.1AA.
University of Southampton
1993
Ogborne, Darren Michael
(1993)
The structure and electric properties of thallium-based superconductors.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Comprehensive studies of the synthesis conditions for preparing thallium cuprate superconductors in bulk quantities have been carried out. The n= 2, 3 and 4 members of the homologous series Tl2Ba2Ca(n-1)CunO2n+4 havebeen prepared by reaction of the component oxides and precursors and the optimum preparative conditions for the reproducible synthesis of these materials have been identified. The formation and superconducting properties of these phases were found to be strongly dependent upon the nominal composition and synthetic environment. The effect of various parameters such as reaction temperature, time, precursor, composition and atmosphere on phase formation and Tc were ascertained. Starting stoichiometries of x= 0, 0.2 and 0.5 in the series Tl2-xBa2Ca(n-1+x)CunO2n+4were required for the formation of bulk phase material corresponding to n= 2, 3 and 4 respectively. The optimum conditions of synthesis were identified as; 890oC for 6 hours in oxygen (for n= 2), 890oC for 6 hours in oxygen (for n= 3), and 860oC for 10 hours in air (for n= 4), each followed by a slow cool to room temperature to ensure an even distribution of oxygen throughout the material. Annealing in atmospheres of argon and oxygen (up to pressures of 500 atm.) was found to induce changes in Tc in the c lattice parameter.
Detailed powder neutron diffraction studies were carried out at the HRPD facility, ISIS on 2212 and 2223 and revealed that the crystal sturctures were very sensitive to slight changes in the oxygen content. The a lattice parameter was found to be about 3.85AA in all materials and was almost invariant to changes in the oxygen content as a result of the in-plane rigidity of the Cu-O bonds. However, the c parameter, at 29.3AA for n= 2, 35.6AA for n = 3 and 42.0AA for n = 4, was found in each to decrease with increasing oxygen content. In the TI-O portion of the structure thallium was found to reside in a strongly distorted octahedron with two short apical bonds of typically 2.0AA, and two moderate and two long bonds in the a-b-plane at 2.4AA and 3.1AA.
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Published date: 1993
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Local EPrints ID: 462330
URI: http://eprints.soton.ac.uk/id/eprint/462330
PURE UUID: d720aa07-51ca-449a-84ca-7ea6990a6324
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Date deposited: 04 Jul 2022 19:05
Last modified: 04 Jul 2022 19:05
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Author:
Darren Michael Ogborne
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