Thesis
Dynamics and structural complexity of framework materials
- Abstract:
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This thesis aims to understand the key phonon modes and chemical interactions that drive phase transitions and thermal expansion in a series of relatively simple inorganic solids. Coarse-graining and thermal diffuse scattering are used to help rationalise the key interactions involved. There are five studies.
The first uses a combination of DFT phonon calculations, inelastic neutron scattering and thermal diffuse scattering to probe the low-energy dynamics of Rb2Zn(CN)4 and K2Zn(CN)4. The A-site (Rb+ and K+) pyrochlore sublattice is shown to play an important role in the dynamics of these systems.
The second concerns dicalcium barium propionate and the origin of its diffuse scattering. Dicalcium barium propionate has a complex structure that makes ab initio phonon calculations intractable. Parallels are drawn between its underlying Ba(Ca)2 framework and SiO2 cristobalite to build a coarse-grained model. Molecular dynamics simulations are then used to understand the nature of the diffuse scattering of dicalcium barium propionate.
The third addresses the negative thermal expansion behaviour of Zn(CN)2 and Cd(CN)2. A combination of neutron total scattering measurements and ab initio phonon calculations are used to reassess the microscopic origin that drives the dominant lattice dynamics. A simple, coarse-grained model turns out to capture the key negative thermal expansion behaviour of M(CN)2, especially at low temperatures.
The fourth investigates whether an automated, coarse-grained approach can capture the low-energy dynamics of framework materials in more general terms. Its effectiveness is then discussed for a variety of chemically-different framework materials namely: MOF-5, [NH4][Zn(HCOO)3] and Zn(CN)2.
The fifth tackles the disordered stacking arrangement of Ni(CN)2. An interlayer potential that encodes the effective interactions between layers is derived. The stacking behaviour of Ni(CN)2 is then re-cast as a pseudo-spin model. Monte Carlo simulations at different temperatures are then run, and the final configurations directly compared to experiment.
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- Files:
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(Preview, Dissemination version, pdf, 28.4MB, Terms of use)
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Authors
Contributors
+ Goodwin, A
- Institution:
- University of Oxford
- Division:
- MPLS
- Department:
- Chemistry
- Role:
- Supervisor
- ORCID:
- 0000-0001-9231-3749
+ Deringer, V
- Institution:
- University of Oxford
- Division:
- MPLS
- Department:
- Chemistry
- Role:
- Supervisor
+ Regoutz, A
- Institution:
- University of Oxford
- Division:
- MPLS
- Department:
- Chemistry
- Role:
- Examiner
+ Philips, A
- Role:
- Examiner
- DOI:
- Type of award:
- DPhil
- Level of award:
- Doctoral
- Awarding institution:
- University of Oxford
- Language:
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English
- Keywords:
- Subjects:
- Deposit date:
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2025-10-26
- ARK identifier:
Terms of use
- Copyright holder:
- Quentin Gueroult
- Copyright date:
- 2025
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