Diao, Jiecheng;
(2022)
Ferroelectric domains in barium titanate by Bragg coherent X-ray diffraction imaging.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
My PhD work focused on studying the domain structures and the strain fields inside barium titanate (BaTiO3) nanocrystals. The results on the domain structure study have already been published. The results on the stripe-like strain fields inside nanocrystals are finalized and there is a plan for publication. The first question my PhD work wants to address is what the domain structures inside BTO nanoparticles exist and how they evolve with temperature and when crossing the phase transition. Bragg coherent X-ray diffraction imaging (BCDI) experiments on nominal 200 nm size BTO nanoparticles were carried out at the Diamond I13-1 beamline and the Advanced Photon Source 34-ID-C beamline. The 90° domain walls were tracked in detail when crossing the tetragonal-cubic phase transition. This is presented in Chapter 3. Upon studying the domain structure inside BTO nanocrystals, some unexpected stripe-like strain fields were found. Crystals with clear facets were chosen to restore resolve the crystallographic direction, after which the strain field direction and periodicity were studied in detail. This is shown in Chapter 4. To understand the temperature dependence of the strain stripes, in-situ BCDI experiments were done at ESRF ID-01 beamline. Faceted BTO nanocrystals were chosen for temperature study. The strain stripes were found to be stable and preserved at both tetragonal and cubic phase with at elevated temperatures. This is illustrated in Chapter 5. The Finite element analysis (FEA) approach was utilized to understand the origins of the strain stripes. Different piezoelectric blocks were defined to simulate the domain structures inside a BTO crystal. 180° domain walls were found to give more strain stripes features than 90° domain walls in the simulation. This is covered in Chapter 6. The same patch of BTO nanocrystals were also studied using an X-ray Free-electron Laser as a function of time delay after laser excitation. Rather than seeing any significant thermal expansion effects, the diffraction peaks were found to move perpendicular to the momentum transfer direction. This suggests a laser driven rotation of the crystal lattice, which is delayed by the aggregated state of the crystals. Internal deformations associated with crystal contacts were also observed. These are shown in Chapter 7.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Ferroelectric domains in barium titanate by Bragg coherent X-ray diffraction imaging |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10162058 |
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