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Investigating new photoactive ferroelectrics using dynamic X-ray diffraction techniques

Morris, Joshua 2024. Investigating new photoactive ferroelectrics using dynamic X-ray diffraction techniques. PhD Thesis, Cardiff University.
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Abstract

The work detailed in this thesis focusses on the development and in-situ X-ray crystallographic investigation of two series of multiresponsive hybrid organic-inorganic materials with pseudo-cubic architectures: (i) based on the nitroprusside ion, of the general formula A[NaFe(CN)5(NO)].xH2O; and (ii) based on Prussian Blue Analogues of the general formula A[CoFe(CN)6].xH2O, where A = an organic ammonium cation. Full characterisation, along with in-situ photo-/crystallographic and ex-situ dielectric analysis was utilised to study these judiciously designed nitroprusside-based materials. This provided insight into the structural and mechanistic factors influencing both the thermally- and electric field-induced phase transitions, as well as the coexistent photoswitching behaviours observed herein. These combined dielectric, computational structural dynamics, and crystallographic studies aimed to reveal any correlations between the responses to individual external stimuli, determining that the inherent photoinduced linkage isomerism (PLI) of these nitroprusside-based materials is not correlated to the thermal- and electric-field responses, hence guiding future rational design of perovskite photovoltaics. A combined crystallographic and spectroscopic investigation of the functionalised Prussian Blue Analogues (PBAs) presented herein was undertaken to confirm the synthesis of these materials. Analysis performed on those PBAs which could be generated in this work revealed significant steric constraints imposed by the anionic Co-Fe framework, which has implications for the rational design of these materials as multiresponsive photovoltaics. A background and introduction to the field of solar energy capture materials and techniques is provided in Chapter 1, along with a review of current research towards the development of efficient photoresponsive spin-crossover and linkage isomer complexes, and ferroelectrics. The overall objectives of this work is also summarised herein. Chapter 2 details from first principles the X-ray crystallographic method, including more recent advancements in photocrystallographic and other dynamic in-situ techniques. A background covering the X-ray structure solution and refinement process is also provided. Chapter 3 represents the major results chapter of this work, focussing on the development, characterisation, and investigation of a series of organic cation modified sodium nitroprusside hybrid organic-inorganic perovskite analogues. In-situ photo-/crystallographic and exsitu dielectric experiments are detailed in Chapter 3, by which the thermally- and electric field-induced phase transitions observed in these materials were studied, along with the nitrosyl photoswitchable linkage isomerism exhibited by each analogue. A brief summary of complementary computational analysis is also detailed in Chapter 3, with a full description of the methods used and results obtained provided in the Appendix. Work towards the synthesis and characterisation of a series of Co-Fe Prussian Blue Analogues, designed as simple representations of flexible photoresponsive metal- - Page 6 - organic frameworks (MOFs) structures is presented in Chapter 4. The overall conclusions resulting from this thesis are presented in Chapter 5, in addition to a number of suggestions for potential avenues of future research in the field. Chapter 6 provides the details of all synthetic and experimental procedures conducted throughout this work.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Funders: The Royal Society, Cardiff University
Date of First Compliant Deposit: 17 July 2024
Last Modified: 17 Jul 2024 13:54
URI: https://orca.cardiff.ac.uk/id/eprint/170638

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