Complex metal oxide materials : synthesis, structural characterisation and development of combined EXAFS and powder diffraction analysis
Complex metal oxide materials : synthesis, structural characterisation and development of combined EXAFS and powder diffraction analysis
A method which allows the simultaneous refinement of x-ray powder diffraction data and one or more EXAFS spectra from the same sample using a single set of coordinates to describe the structure, has been tested by application to a range of inorganic materials. This method combines the long range structure obtained from powder diffraction, with that of the local environment of one or more of the atoms in a structure, available from EXAFS. This method allows better determination of the position of oxygen atom and other light atoms in materials where the diffraction pattern is dominated by heavy atoms, and the determination of the occupancy of sites where elements of similar scattering amplitude are involved. The combined refinement program has been applied to a number of different systems; the structure determination of the complex oxide Gd2Ba2CaCu2Ti3O14 has been undertaken using a combination of EXAFS data from all five of the metals with powder x-ray diffraction data and the structure refined using a single set of coordinates to fit all of the experimental data. A new model for the structure of gallobicchulite, Ca8(Ga2SiO6)4(OH)8, is given, based on a combined EXAFS and neutron powder diffraction refinement. The structure of Cs2TeO4 has been studied using the combined refinement of tellurium K-edge EXAFS and powder X-ray diffraction data and discrete tetrahedral TeO42- groups have been found for the first time in a simple tellurate.
The synthesis and characterisation of members of the quintuple copper titanium perovskite series Ln2Ba2CaCu2Ti3O14 were investigated. Structural characterisation, carried out by a combination of powder x-ray and powder neutron diffraction and EXAFS, shows full ordering of the cations for Ln - Sm, Eu, Gd, in the tetragonal space group P4/mmm with the B type cations stacked in the order Cu-Ti-Ti-Ti-Cu. For Ln = Pr, Nd partial disorder on both the A and B cation sublattices occurs and oxygen is incorporated between the CuO2 layers. For Ln = La there is full disordering on both the A and B cation lattices leading to a simple cubic unit cell. When Ln = Tb, Dy, the symmetry of the structure is reduced to an orthorhombic cell, though the B cation stacking is maintained. In all materials including novel doped phases, the TiO6 octahedra are distorted. The in-plane distances of ~1.93 A are similar to those found in high-temperature superconductors.
University of Southampton
1998
Pack, Maria Joyce
(1998)
Complex metal oxide materials : synthesis, structural characterisation and development of combined EXAFS and powder diffraction analysis.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
A method which allows the simultaneous refinement of x-ray powder diffraction data and one or more EXAFS spectra from the same sample using a single set of coordinates to describe the structure, has been tested by application to a range of inorganic materials. This method combines the long range structure obtained from powder diffraction, with that of the local environment of one or more of the atoms in a structure, available from EXAFS. This method allows better determination of the position of oxygen atom and other light atoms in materials where the diffraction pattern is dominated by heavy atoms, and the determination of the occupancy of sites where elements of similar scattering amplitude are involved. The combined refinement program has been applied to a number of different systems; the structure determination of the complex oxide Gd2Ba2CaCu2Ti3O14 has been undertaken using a combination of EXAFS data from all five of the metals with powder x-ray diffraction data and the structure refined using a single set of coordinates to fit all of the experimental data. A new model for the structure of gallobicchulite, Ca8(Ga2SiO6)4(OH)8, is given, based on a combined EXAFS and neutron powder diffraction refinement. The structure of Cs2TeO4 has been studied using the combined refinement of tellurium K-edge EXAFS and powder X-ray diffraction data and discrete tetrahedral TeO42- groups have been found for the first time in a simple tellurate.
The synthesis and characterisation of members of the quintuple copper titanium perovskite series Ln2Ba2CaCu2Ti3O14 were investigated. Structural characterisation, carried out by a combination of powder x-ray and powder neutron diffraction and EXAFS, shows full ordering of the cations for Ln - Sm, Eu, Gd, in the tetragonal space group P4/mmm with the B type cations stacked in the order Cu-Ti-Ti-Ti-Cu. For Ln = Pr, Nd partial disorder on both the A and B cation sublattices occurs and oxygen is incorporated between the CuO2 layers. For Ln = La there is full disordering on both the A and B cation lattices leading to a simple cubic unit cell. When Ln = Tb, Dy, the symmetry of the structure is reduced to an orthorhombic cell, though the B cation stacking is maintained. In all materials including novel doped phases, the TiO6 octahedra are distorted. The in-plane distances of ~1.93 A are similar to those found in high-temperature superconductors.
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Published date: 1998
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Local EPrints ID: 463213
URI: http://eprints.soton.ac.uk/id/eprint/463213
PURE UUID: aabac9f3-6983-4e75-b597-d6caee42bddc
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Date deposited: 04 Jul 2022 20:47
Last modified: 04 Jul 2022 20:47
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Author:
Maria Joyce Pack
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