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Symmetry adapted analysis of lattice dynamics and local distortions in perovskite related materials
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Bird, Tobias A. (2021) Symmetry adapted analysis of lattice dynamics and local distortions in perovskite related materials. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3747763
Abstract
The work presented in this thesis considers the effect of dynamic and static distortions on the local structure of perovskite-related materials. I systematically interrogate the pair distribution functions of the materials against phonon eigenvectors, determined using representation theory. I present the method for performing this Symmetry-Adapted Pair Distribution Function Analysis (SAPA) in chaper 2.
In the chapters 3 and 4, I perform this SAPA technique on the negative thermal expansion (NTE) materials ScF3, CaZrF6 and ReO3. NTE is usually viewed as originating from a vibrational tension effect, commonly realised in materials via cooperative rotations of atomic polyhedra, termed rigid unit modes (RUMs). The results of our SAPA analysis show that scissoring modes, which distort the octahedral bond angles, dominate the local structure in ScF3 and CaZrF6 but not ReO3, rather than the RUMs one might expect. I therefore conclude that structural flexibility is a key determining factor in the extent and magnitude of NTE observed in a material.
This theme of the importance of structural flexibility, in the form of scissoring modes, continues in the final results chapter. In this work, the local structure of the cubic phases of the methylammonium lead halides are analysed using the SAPA technique. We find that in all three hybrid perovskites studied, scissoring modes again describe the largest deviation from the average structure. These modes have a larger amplitude for these hybrid perovskites than for ScF3, despite the presence of A-sites in the former. Using Density Functional Theory calculations, we show that these modes are linked to an opening of the electronic band gap.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Library of Congress Subject Headings (LCSH): | Perovskite materials, Lattice dynamics, Phonons, Eigenvectors | ||||
Official Date: | August 2021 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Senn, Mark S. ; Bristowe, Nicholas | ||||
Format of File: | |||||
Extent: | xii, 126, 1-5 leaves : illustrations | ||||
Language: | eng |
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