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Investigation of the structure and phase transitions in the novel A-site substituted perovskite series (Na1-xKx)0.5Bi0.5TiO
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Jones, Glyn Owen (2001) Investigation of the structure and phase transitions in the novel A-site substituted perovskite series (Na1-xKx)0.5Bi0.5TiO. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b1374283~S15
Abstract
An extensive study of the crystal structure and phase transitions in Na0.5Bi0.5TiO3
has been carried out using neutron/x-ray powder, and single-crystal x-ray, diffraction
techniques. This has been complemented with optical and Raman studies. The sequence
of phase transitions from the high-temperature prototypic cubic structure (above 813 K),
to one of tetragonal (673-773 K) and then rhombohedral structure (5-528 K) has been
established in Na0.5Bi0.5TiO3. Coexisting tetragonal/cubic (773-813 K) and
rhombohedral/tetragonal (528-673 K) phases have also been observed. Rietveld
refinements have revealed the rhombohedral phase, space group Ric, exhibits an
antiphase, a-a-a- oxygen octahedra tilt system, with parallel cation displacements. The
tetragonal phase, space group P4bm, possesses an unusual combination of in-phase,
a0a0c+ oxygen octahedra tilts and antiparallel cation displacements along the polar axis.
This structure type is unprecedented amongst the perovskites. A high-pressure study
using synchrotron and neutron diffraction has revealed the ambient pressure
rhombohedral structure undergoes a phase transition to an orthorhombic structure with
Pnma symmetry and the a-b+a- oxygen octahedra tilt system together with antiparallel A-cation
ordering along [010]. The pure rhombohedral structure persists up to 8 kbar;
between 10-19.4 kbar a rhombohedral/orthorhombic coexistence region was observed
and above 26.2 kbar the purely orthorhombic phase was seen.
Structural variations as a function of temperature, pressure and doping across the
(Na1-xKx)0.5Bi0.5TiO3 series are also presented. With increasing potassium doping across
this series, phase transitions from the rhombohedral structure with octahedral tilting to a
non-tilted rhombohedral structure (space group, Ram) and then to a tetragonal structure
(space group P4mm) was observed. A basic phase diagram for this series has been
assembled outlining phase boundaries across the series and as a function of temperature.
In this study, the optimum conditions used for the fabrication of powders,
ceramics and single crystals of the perovskite compound Na0.5Bi0.5TiO3 and the solid
solution across the (Na1-xKx)0.5Bi0.5TiO3 series have been established. A detailed analysis
of this A-site substituted distorted perovskite compound is made with structural
variations, cation displacements and octahedral distortions for the different phases being
reported. The A-site substituted compounds are thoroughly discussed in the context of
modem perovskite science.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | Perovskite, Crystals, Materials -- Thermal properties, Phase transformations (Statistical physics) | ||||
Official Date: | March 2001 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Thomas, Pam A. | ||||
Sponsors: | Engineering and Physical Sciences Research Council (EPSRC) | ||||
Extent: | xvi, 218 p. | ||||
Language: | eng |
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