Topological mechanics in quasicrystals

We study topological mechanics in two-dimensional quasicrystalline parallelogram tilings. Topological mechanics has been studied intensively in periodic lattices in the past a few years, leading to the discovery of topologically protected boundary floppy modes in Maxwell lattices. In this paper we extend this concept to quasicrystalline parallelogram tillings and we use the Penrose tiling as our example to demonstrate how these topological boundary floppy modes arise with a small geometric perturbation to the tiling. The same construction can also be applied to disordered parallelogram tilings to generate topological boundary floppy modes. We prove the existence of these topological boundary floppy modes using a duality theorem which relates floppy modes and states of self stress in parallelogram tilings and fiber networks, which are Maxwell reciprocal diagrams to one another. We find that, due to the unusual rotational symmetry of quasicrystals, the resulting topological polarization can exhibit orientations not allowed in periodic lattices. Our result reveals new physics about the interplay between topological states and quasicrystalline order, and leads to novel designs of quasicrystalline topological mechanical metamaterials.Comment: 16 pages, 8 figure

Structure-Property Relationships in Oxide-Ion Conductors

Literature review: Details the structure-property relationships of a selection of oxide-ion conductors and their potential use as solid electrolytes. Experimental methods: Describes the synthesis methods and analytical techniques used during this project. Structural characterisation and properties of the Bi1–xNbxO1.5+x materials (x = 0.0625, 0.11, and 0.12): The characterisation of tetragonal Bi0.9375Nb0.0625O1.5625 is reported for the first time. Thermal annealing of Bi0.89Nb0.11O1.61 and Bi0.88Nb0.12O1.62 resulted in decreases in oxide-ion conductivity due to partial cubic-to-tetragonal phase transitions. The structure-property relationships of Bi(III)-containing apatite-type oxide-ion conductors: The first Bi(III)-containing triclinic apatite, Bi2La8[(GeO4)6]O3, was characterised, with annular bright-field scanning-transmission electron microscopy directly imaging small concentrations of interstitial oxygen. Bond valence energy landscape modelling probed the potential pathways for interstitial oxide-ion migration in apatites. Understanding variable Re coordination environments in Bi28Re2O49: Reverse Monte Carlo analyses of Bi28Re2O49 using neutron total-scattering data found the local-scale structure to contain 4-, 5-, and 6-coordinate ReOx polyhedra. At 700 °C, migration of oxygen atoms between the Bi-O and Re-O sublattices occurs. Structure-property relationships of bismuth molybdate compositions, Bi38–xMo7+xO78+3x/2 (x = 0, 0.5): The fluorite-related superstructure of orthorhombic Bi38Mo7O78 was characterised using synchrotron X-ray and neutron diffraction data, with distortion-mode analysis undertaken to attempt to characterise the room-temperature monoclinic phase. Floating-zone-furnace crystal growth of fluorite- and apatite-type oxide-ion conductors: Crystals for a range of materials were grown using a floating-zone furnace, upon which single-crystal Laue neutron diffraction data were subsequently collected. Using this data, the complex rhombohedral superstructure of Bi0.913V0.087O1.587 was characterised. Synthesis, characterisation, and properties of the LaxSr10–xGa6O19+x/2 family (x = 0, 0.2, and 0.4): A range of lanthanum strontium gallates were synthesised to investigate the effect of interstitial oxygen content on the oxide-ion conductivity of these materials. Conclusions and future work: A summary of the project, including suggestions for future work

Reconstructions at the Interface in Complex Oxide Heterostructures with Strongly Correlated Electrons

Strongly correlated oxides exhibit a rich spectrum of closely competing orders near the localized-itinerant Mott insulator transition leaving their ground states ripe with instabilities susceptible to small perturbations such as lattice distortions, variation in stoichiometry, magnetic and electric fields, etc. As the field of interfacial engineering has matured, these underlying instabilities in the electronic structure of correlated oxides continue to be leveraged to manipulate existing phases or search for emergent ones. The central theme is matching materials across the interface with disparate physical, chemical, electronic, or magnetic structure to harness interfacial reconstructions in the strongly coupled charge, spin, orbital, and lattice degrees of freedom. In this dissertation, we apply the above paradigm to cuprate-manganite and cuprate-titanate interfaces. We examine ultrathin YBa2Cu3O7/La2/3Ca1/3MnO3 multilayers, where interfacial charge reconstruction modulates the distribution of charge carriers within the superconducting planes and thereby act as dials to tune through the cuprate doping phase diagram. The ultrathin nature of the cuprate layers allows the reconstructed states to be resolved free of a bulk admixture. The depleted carriers are observed to directly enter the CuO2 planes. With increasing manganite thickness, magnetic correlations are introduced, and coupling between interfacial Cu and Mn develops. The reconstructions in spin and electronic degrees of freedom found in cuprate-manganite heterostructures are expected to completely mask all other competing interactions. To this end, SrTiO,3 is incorporated as a spacer material in cuprate-titanate multilayers to reveal the role of dimensionality, interlayer coupling, and broken translational symmetry. At the unit cell limit, a decrease in carrier concentration is found that directly correlates with underdoping from lost charge reservoir layers at the interface, while increased titanate layer thickness is found to augment the carrier concentration with the charge reservoir layers but has no effect on the doping within the superconducting planes. Also spectroscopic evidence for charge transfer across the interface between Cu and Ti is shown to support a recent theoretical prediction of pre-doping at the cuprate-titanate interface in response to a polar discontinuity at the interface

Technology 2001: The Second National Technology Transfer Conference and Exposition, volume 1

Papers from the technical sessions of the Technology 2001 Conference and Exposition are presented. The technical sessions featured discussions of advanced manufacturing, artificial intelligence, biotechnology, computer graphics and simulation, communications, data and information management, electronics, electro-optics, environmental technology, life sciences, materials science, medical advances, robotics, software engineering, and test and measurement

High Throughput Software for Powder Diffraction and its Application to Heterogeneous Catalysis

In this thesis we investigate high throughput computational methods for processing large quantities of data collected from synchrotrons and their application to spectral analysis of powder diffraction data. We also present the main product of this PhD programme, specifically a software called 'EasyDD' developed by the author. This software was created to meet the increasing demand on data processing and analysis capabilities as required by modern detectors which produce huge quantities of data. Modern detectors coupled with the high intensity X-ray sources available at synchrotrons have led to the situation where datasets can be collected in ever shorter time scales and in ever larger numbers. Such large volumes of datasets pose a data processing bottleneck which augments with current and future instrument development. EasyDD has achieved its objectives and made significant contributions to scientific research. It can also be used as a model for more mature attempts in the future. EasyDD is currently in use by a number of researchers in a number of academic and research institutions to process high-energy diffraction data. These include data collected by different techniques such as Energy Dispersive Diffraction, Angle Dispersive Diffraction and Computer Aided Tomography. EasyDD has already been used in a number of published studies, and is currently in use by the High Energy X-Ray Imaging Technology project. The software was also used by the author to process and analyse datasets collected from synchrotron radiation facilities. In this regard, the thesis presents novel scientific research involving the use of EasyDD to handle large diffraction datasets in the study of alumina-supported metal oxide catalyst bodies. These data were collected using Tomographic Energy Dispersive Diffraction Imaging and Computer Aided Tomography techniques.Comment: thesis, 202 pages, 95 figures, 6 table