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Abstract: The central theme of this thesis is the application of radial and pair distribution function analysis to materials characterisation problems for nanotechnology. These concepts are introduced in Chapter 1, and the associated methods are described in Chapter 2. Chapter 3 details the first of the results which discusses the design and development of a software tool called ImageDataExtractor. This auto-extracts microscopy images and then analyses them to afford quantitative information regarding particles in a sample, such as shape, size and distribution. It realises an opportunity for data-mining the ubiquity of readily available images in the literature. Chapter 4 presents results of the development and execution of a novel experimental technique, called glancing-angle pair distribution function (gaPDF) analysis, applied to the structure of the working electrode in dye-sensitised solar cells (DSSCs). This structure was successfully observed, validating this novel method. The investigation also suggested preferred binding modes of the carboxylic acid anchoring groups present in this interfacial structure. Chapters 5 and 6 demonstrate the application of PDF analysis to synchrotron-based powder diffraction data of two material case studies: the rare earth phosphate glass (REPG) (Gd2O3)0.230(P2O5)0.770, and four Ru based photo-isomers. The closest R…R rare earth separation, which governs optical properties of REPGs, was determined to be 4.2(1) Å, aided by various statistical techniques. Analysis on four Ru-based photo-isomers confirmed: the existence of local structure in such compounds, their ability to be photo-isomerised in powder form, the theoretical models constructed using computational techniques, and the lack of heterogeneity in photo-isomerisation throughout a given light-induced sample. Chapter 7 concludes the work and offers a future outlook.

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Abstract: To understand the importance of the crystallite size on the stabilization of metastable tetragonal ZrO2, ultra-fine ZrO2 nanocrystallites were synthesized via: (i) the precipitation method in supercritical water using nitrate precursors, (ii) the sol-gel method in a supercritical ethanol-water mixture and (iii) the borderline non-hydrolytic sol-gel route in supercritical ethanol using propoxide precursors. The obtained nanocrystals displayed a variation of the monoclinic versus tetragonal molar frac-tions from 100 wt. % down to ≈ 10 wt. % of monoclinic. This variation was concomitant with an overall size decrease of the nanocrystals, ranging from 7 to 2 nm depending on the synthesis procedures. Phase contents were quantified by refinement analysis of X-ray scattering datasets, and crosschecked with Raman spectroscopy. Our results suggest that an upper limit of ≈ 90 wt. %, of tetragonal ZrO2 phase is possible, even for ultra-fine nanoparticles (2 nm). These findings thus question the exist-ence of any critical size limit below which stabilization of pure t-ZrO2 is attainable at low temperatures.

Open Access

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Abstract: Lithium conducting garnets are attractive solid electrolytes for solid-state lithium batteries but are difficult to process, generally requiring high reaction and sintering temperatures with long durations. In this work, we demonstrate a synthetic route to obtain Ta-doped garnet (Li6.4La3Zr1.4Ta0.6O12) utilizing La- and Ta-doped lanthanum zirconate (La2.4Zr1.12Ta0.48O7.04) pyrochlore nanocrystals as quasi-single-source precursors. Via molten salt synthesis (MSS) in a highly basic flux, the pyrochlore nanocrystals transform to Li-garnet at reaction temperatures as low as 400 °C. We also show that the pyrochlore-to-garnet conversion can take place in one step using reactive sintering, resulting in densified garnet ceramics with high ionic conductivity (0.53 mS cm−1 at 21 °C) and relative density (up to 94.7%). This approach opens new avenues for lower temperature synthesis of lithium garnets using a quasi-single-source precursor and provides an alternative route to highly dense garnet solid electrolytes without requiring advanced sintering processes.

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Abstract: Hydrogen storage in a suitable form has the highest possible storage capacity, cyclic ability, stability of the applied material and long-term sustainability; all these are the key factors that influence further industrial development in the world. The final product of the hydrogen combustion process is water and the specific energy of hydrogen is three times higher than nowadays used exhaustible energy sources. This work is focused on the preparation of materials with the amorphous character capable safely store hydrogen and its energy in the structure by chemical bonds. Ternary and quaternary materials based on Mg, Ni, Ce, and Cu were selected as starting materials. All compositions were prepared at the Institute of Materials Research of Slovak Academy of Sciences in Košice in the form of ribbons by melt spinning method. Microstructural observations of the prepared materials in the ribbon form were performed by means of optical microscopy and scanning electron microscopy. Thermal stability and specific transformation temperatures were ascertain by means of differential scanning calorimeter. Amorphous alloys were powdered by milling in a high-energy planetary mill. Their size below 100 μm was used to study the storage capacity of hydrogen and deuterium. Deuterium gas has been selected mainly for further neutron diffraction experiments. The storage capacities of deuterium and hydrogen in the amorphous samples were tested at the INC Leipzig and Faculty of Mechanical Engineering, Technical university in Košice. Based on the series of experiments, it was possible to determine storage capacity of hydrogen and deuterium of the selected materials, to analyse the effect of Cu substitution on desorption conditions, describe structure of the amorphous Mg60Ni30Ce10, determine phase transitions and their products.

Open Access

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Abstract: Interactions between extended π-systems are often invoked as the main driving force for stacking and crystallization of 2D organic polymers. In covalent organic frameworks (COFs), the stacking strongly influences properties such as the accessibility of functional sites, pore geometry, and surface states, but the exact nature of the interlayer interactions is mostly elusive. The stacking mode is often identified as eclipsed based on observed high symmetry diffraction patterns. However, as pointed out by various studies, the energetics of eclipsed stacking are not favorable and offset stacking is preferred. This work presents lower and higher apparent symmetry modifications of the imine-linked TTI-COF prepared through high- and low-temperature reactions. Through local structure investigation by pair distribution function analysis and simulations of stacking disorder, we observe random local layer offsets in the low temperature modification. We show that while stacking disorder can be easily overlooked due to the apparent crystallographic symmetry of these materials, total scattering methods can help clarify this information and suggest that defective local structures could be much more prevalent in COFs than previously thought. A detailed analysis of the local structure helps to improve the search for and design of highly porous tailor-made materials.