The synthesis and characterisation of oxide metal-insulator materials
The synthesis and characterisation of oxide metal-insulator materials
Ca2Os2O7 has been synthesised by the direct reaction of the component oxides in a sealed silica ampoule at ambient pressure. The structure of this system has been determined from analysis of neutron diffraction data. The material was found to adopt a stoichiometric, orthorhombic weberite structure type rather than the more usual cubic pyrochlore structure. The distortion of the OsO6 octahedra and eightfold Ca-O co-ordinations decrease with increasing temperature, indicating that this material lies close to the weberite/pyrochlore phase boundary. The electronic behaviour of Ca2Os2O7 has been measured by recording variable temperature conductivity measurements showing a metal-insulator transition across room temperature.
The pyrochlores Pb2Os2O7-x and Tl2Os2O7-x have been synthesised and characterised using powder x-ray and neutron diffraction. Analysis of the data confirmed the presence of oxygen vacancies in the lattice, which was determined as cubic Fd-3m. There is a mixing of oxidation states on the ‘A’ cation site for both materials.
The only known superconducting pyrochlore, Cd2Re2O7, has been prepared at ambient pressure using a 114Cd isotope to enable power neutron diffraction data collection. The structure for Cd2Re2O7 between 320 mK and room temperature has been investigated and a model has been proposed for the superconducting phase. The low temperature (<200K) structure of Cd2Re2O7 was modelled in the space group F-43m, where a marked distortion of the ReO octahedra was found to occur. Positional displacements in both the rhenium and oxygen sub-lattices contributed to the distortion, producing a trigonal environment for the rhenium atoms.
A complete solid solution between metallic LaNiO3 and insulating LaAlO3 has been synthesised using a precursor citrate gel technique at ambient pressure. The results show a significant increase in resistivity for ≥ 60% aluminium concentration.
University of Southampton
Reading, Jon
1b939af6-d283-40e5-9fa2-87ae49c7d341
2003
Reading, Jon
1b939af6-d283-40e5-9fa2-87ae49c7d341
Reading, Jon
(2003)
The synthesis and characterisation of oxide metal-insulator materials.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Ca2Os2O7 has been synthesised by the direct reaction of the component oxides in a sealed silica ampoule at ambient pressure. The structure of this system has been determined from analysis of neutron diffraction data. The material was found to adopt a stoichiometric, orthorhombic weberite structure type rather than the more usual cubic pyrochlore structure. The distortion of the OsO6 octahedra and eightfold Ca-O co-ordinations decrease with increasing temperature, indicating that this material lies close to the weberite/pyrochlore phase boundary. The electronic behaviour of Ca2Os2O7 has been measured by recording variable temperature conductivity measurements showing a metal-insulator transition across room temperature.
The pyrochlores Pb2Os2O7-x and Tl2Os2O7-x have been synthesised and characterised using powder x-ray and neutron diffraction. Analysis of the data confirmed the presence of oxygen vacancies in the lattice, which was determined as cubic Fd-3m. There is a mixing of oxidation states on the ‘A’ cation site for both materials.
The only known superconducting pyrochlore, Cd2Re2O7, has been prepared at ambient pressure using a 114Cd isotope to enable power neutron diffraction data collection. The structure for Cd2Re2O7 between 320 mK and room temperature has been investigated and a model has been proposed for the superconducting phase. The low temperature (<200K) structure of Cd2Re2O7 was modelled in the space group F-43m, where a marked distortion of the ReO octahedra was found to occur. Positional displacements in both the rhenium and oxygen sub-lattices contributed to the distortion, producing a trigonal environment for the rhenium atoms.
A complete solid solution between metallic LaNiO3 and insulating LaAlO3 has been synthesised using a precursor citrate gel technique at ambient pressure. The results show a significant increase in resistivity for ≥ 60% aluminium concentration.
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Published date: 2003
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Local EPrints ID: 465195
URI: http://eprints.soton.ac.uk/id/eprint/465195
PURE UUID: d7b6dfd7-457f-421e-a9a4-e7483e078a1b
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Date deposited: 05 Jul 2022 00:28
Last modified: 16 Mar 2024 20:01
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Author:
Jon Reading
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