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The synthesis and characterisation of oxide metal-insulator materials

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
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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