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

Nanoparticles/polysaccharide nanocomposites for water purification

The main objective of this study was to synthesise of nanocomposites made of nanoparticles and cellulose or cellulose derivatives for the use of these in water purification. A variety of different kinds of nanoparticles were synthesised using similar approaches. Chapters one and two contain a literature review, introduction and technical information about the instruments. Chapter three includes all the experimental methodologies that have been used in general, while more details are giving late as required. Then, five chapters are about the synthesis and characterisation of specified nanocomposites and in each of these five chapters, water remediation was attempted.In chapter four, spherical silver nanostructures were synthesised in aqueous media and attached to cellulose paper: an environmentally porous support. The general method of synthesis was based on attaching Ag+ ions in the cellulose substrate then reducing these ions with sodium borohydride, a mild reducing agent. Different reaction conditions were investigated, for example precursors concentration and use of a stabiliser. The silver/cellulose nanocomposite was characterised with different analytical techniques. Silver nanoparticles appear as face-centred cubic (fcc) crystals of pure metallic silver. The quantity of silver nanoparticles was proportional to the concentration of silver ions in the precursor solution. Additional stabilised cellulose had a non-negligible impact: the investigations showed that its presence of them enhances the amount of silver nanoparticles immobilised in the samples. Moreover, it does not change the morphology of silver nanoparticles, although it helps keep these nanoparticles dispersed.In chapter five, nanocomposites were fabricated by interacting dispersion of nanoparticles with a support. First, a yellow dispersion of silver nanoparticles was synthesised by a chemical reduction method. The resulting dispersion of silver nanoparticles was stabilised by electrostatic forces. Attention was focused on the effect of temperature and addition method during the reduction step. The morphology of nanoparticles was investigated by quantitative and qualitative analytical techniques. Silver nanoparticles were spherical with a size of 17 nm ± 5.6, and shown to adsorb light ~ 400 nm due to surface plasmon resonance (SPR). The colloidal silver nanoparticles were put in contact with cellulose triacetate to prepare the composites. The process of adsorption was controlled by varying the pH of the dispersion. The coverage of silver nanoparticles over a solid substrate was evaluated by ICP analysis and visual observation. pH has a great impact on the improvement of quantity of silver nanoparticles over the surface; a homogenous yellow coverage of silver nanoparticles over cellulose triacetate was obtained at higher pH. Positive antibacterial action was observed from the silver cellulose triacete nanocomposites against MRSA.In chapter six, the electrochemical-behaviour of silver cellulose nanocomposites was investigated in relation to various parameters, i.e., the concentration of silver nanoparticles, electrolytes and concentration of electrolyte. The stripping of silver cellulose nanocomposites may depend on the size of the nanoparticles and the coverage of silver nanoparticles in the sample. Small nanoparticles showed a very sharp oxidation peak. However, polydispersed nanoparticles had slow and complex redox pattern. The peak potential varied with change in the electrolyte. The oxidation of silver nanoparticles was very sensitive to chloride ions. PXRD patterns confirmed the formation of silver chloride and silver nitrate. Silver cellulose nanocomposites have great potential in water purification.In chapter seven, cobalt nanoparticles was prepared by two synthetic approaches. The first approach involved the preparation of aqueous dispersions of cobalt nanoparticles by reduction of metal salt using sodium borohydride. A number of procedure conditions were investigated such as the precursor’s concentration, reduction time and temperature. In the first approach, highly crystalline cobalt nanoparticles with some other compounds were produced after further decomposing. Changing temperature has an impact on the crystal structure. The second approach involved saturating the porous, absorptive substrate with an aqueous solution of cobalt salt and then reducing the metal salt using sodium borohydride or hydrogen gas to cobalt nanoparticles in situ on the substrate surface. Cellulose was used to inhibit aggregation and agglomeration of the cobalt nanoparticles. It was likely that chemical reduction using sodium borohydride formed a mixture of spherical crystal and amorphous cobalt nanoparticles. In contrast, reduction by hydrogen gas may produce spherical crystal cobalt nanoparticles Therefore, cellulose substrate and hydrogen gas have potential in green synthesis of cobalt cellulose nanocomposites. The potential for using cobalt nanoparticles in wastewater treatment and a medical setting is high as cobalt nanoparticles mainly showed good antibacterial action against all bacterial isolates tested with zone of inhibition sizes up to 15 mm.In chapter eight, the green synthesis of copper nanoparticles and copper cellulose nanocomposites was carried out using a simple reduction method. Mixtures of copper and copper oxide nanoparticles were synthesised by reduction of copper ions using sodium borohydride, in different reaction conditio ns: concentration, atmosphere, temperature and using a stabiliser. The natural substrate cellulose was used to stabilise the nanoparticles. The physicochemical properties of copper as free nanoparticles and as copper cellulose nanocomposites were investigated. PXRD was used to identify the structure of the copper nanoparticles and show the effect of reaction condition, i.e., concentration precursor on crystal structures. PXRD patterns, TEM images and UV-VIS display the impact of cellulose on nanoparticle size, i.e., the presence of cellulose reduces the size of copper nanoparticles formed. Copper cellulose nanocomposites and copper nanoparticles had only sufficient or limited antibacterial action. Increasing the concentration of copper nanoparticles in samples may improve antibacterial activity

Phase relations, structural studies and physical properties of mixed metal oxides and sulphides

The phase relations in three oxide systems; ZnO–BiVO4, Pb2V2O7–BiVO4 and PbO– BiVO4, have been studied and their phase diagrams over the whole component concentration range up to 1273 K have been established. As a result of solid-state reaction between ZnO and BiVO4 mixed at a molar ratio of 2:1 or among ZnO, V2O5 and Bi2O3, mixed at a molar ratio of 4:1:1, a new double vanadate BiZn2VO6 has been obtained. Its crystallographic system was determined, its unit cell parameters were calculated and its incongruent melting temperature was established. A new compound is also formed in the Pb2V2O7–BiVO4 system. It has been shown that BiVO4 and Pb2V2O7 react with each other forming a compound of the formula Pb2BiV3O11, when their molar ratio is equal to 1:1, or between PbO, Bi2O3 and V2O5, mixed at a molar ratio of 4:1:3. This material melts congruently and it crystallises in the triclinic system. A new series of non-stoichiometric sulphides Ga1-xGexV4S8 (0 x 1) has been synthesised by standard solid-state reaction. The samples have been characterised by powder X-ray and neutron diffraction, SQUID magnetometry and electrical transportproperty measurements. Structural analysis reveals that a solid solution is formed throughout this composition range. Magnetic measurements suggest that the ferromagnetic behaviour of the end-member phase GaV4S8 is retained at x 0.7. By contrast Ga0.25Ge0.75V4S8 appears to undergo antiferromagnetic ordering at ca. 15 K. All materials with x ¹ 1 are n-type semiconductors whose resistivity falls by almost six orders of magnitude with decreasing gallium content, whilst the end-member phase GeV4S8 is a ptype semiconductor. Powder neutron diffraction studies show that the cubic unit cell is retained for non-stoichiometric materials to the lowest temperatures studied. Single crystals of five erbium-chromium sulphides have been grown by chemical vapour transport using iodine as the transporting agent. Single-crystal X-ray diffraction reveals that in Er3CrS6, octahedral sites are occupied exclusively by Cr3+ cations, leading to onedimensional CrS4 5- chains of edge-sharing octahedra, whilst in Er2CrS4, Er3+ and Cr2+ cations occupy the available octahedral sites in an ordered manner. By contrast, in Er6Cr2S11, Er4CrS7 and Er8Cr3S15, Er3+ and Cr2+ ions are disordered over the octahedral sites. In Er2CrS4, Er6Cr2S11, Er4CrS7 and Er8Cr3S15, the network of octahedra generates an anionic framework constructed from M2S5 slabs of varying thickness, linked by onedimensional octahedral chains. This suggests that these four phases belong to a series in which the anionic framework may be described by the general formula [M2n+1S4n+3]x-, with charge balancing provided by Er3+ cations located in sites of high-coordination number within one-dimensional channels defined by the framework. Er4CrS7, Er6Cr2S11, Er8Cr3S15 ii and Er2CrS4 may thus be considered as the n = 1, 2, 3 and members of this series. Whilst Er4CrS7 is paramagnetic, successive magnetic transitions associated with ordering of the chromium and erbium sub-lattices are observed on cooling Er3CrS6 (TC(Cr) = 30 K; TC(Er) = 11 K) and Er2CrS4 (TN(Cr) = 42 K, TN(Er) = 10 K) whereas Er6Cr2S11 exhibits ordering of the chromium sub-lattice only (TN = 11.4 K). These four materials have been studied using neutron diffraction which allowed magnetic ordering to be examined

Crystal structure and phase transitions in various functional perovskites

There has been specific interest over the past decade in the discovery and development of new piezoelectric and ferroelectric materials for the use in functional devices, specifically with the aim of replacing the widespread use of PbZrₓTi₁₋ₓO₃. The work detailed in this thesis focuses on the structural characterisation and thermal behaviour of several perovskites possessing interesting physical characteristics, such as ferroelectricity or magnetism. Structural evolution and phase behaviour is characterised using Rietveld refinement techniques on high resolution powder neutron diffraction data. Additional analytical techniques such as symmetry mode analysis, permittivity measurements and second harmonic generation measurements are also often exploited. The work on the LiₓNa₁₋ₓNbO₃ system demonstrated a susceptibility to softening of the T₄ octahedral tilt mode up to a composition of at least x = 0.12, indicating that the LNN-X solid solution could yield a number of unique perovskite structures. A rationale for how this T₄ mode varies across the composition range is offered. The higher doped composition at a value of x = 0.20, displays even more intriguing structural behaviour with the adoption of not one but two variants of the very rare a⁺a⁺c⁻ Glazer tilt system. A detailed bond length/bond angle analysis as a function of temperature is used to rationalise the nature of the octahedral distortion that drives the c > a crossover in the rare earth orthoferrite LaFeO₃. Symmetry mode analysis is exploited to assist in the structural comparison to the related compound Bi₀.₅La₀.₅FeO₃, highlighting the anomalous behaviour it exhibits as a result of magnetoelectric coupling effects. The nature of the paraelectric – ferroelectric transition in the layered perovskitelike Dion Jacobson phase, CsBi₀.₆La₀.₄Nb₂O₇ is identified as a direct “avalanche” type transition, making it an example of a hybrid improper ferroelectric. Ferroelectricity in this case does not occur as a result of traditional second-order Jahn-Teller distortions, but is achieved via a mechanism known as trilinear coupling. Experimental analysis is important in understanding the intricacies of this trilinear coupling mechanism. Symmetry mode analysis of CsBi₀.₆La₀.₄Nb₂O₇ shows that two zone boundary primary order parameters (M₂⁺ and M₅⁻) associated with octahedral tilting condense simultaneously, and couple to a zone centre ferroelectric distortion mode (Γ₄⁻). The similar temperature dependency for the two octahedral tilt modes excludes the presence of an intermediary phase, suggesting that the trilinear coupling in this layered phase is strong. Detailed structural characterisations such as those highlighted in this thesis are of fundamental importance as they can identify new design-led approaches to functional materials

Polaris-SMC in-situ microwave reactor: a new technique for real time neutron diffraction of rapid microwave-induced syntheses

Direct microwave heating holds much promise in revolutionising the synthesis of solid state materials due to the clear benefits from greatly reduced reaction times and lower energy requirements compared to conventional methods. For the modern laboratory the principles of green chemistry to reduce energy usage and actions with a detrimental impact to the environment are increasingly taking prominence, and microwave reactors work well within this framework. The rapidity of microwave heating however, makes following a reaction progression and identification of unusual synthesis pathways a difficult process. The bespoke single mode cavity reactor designed to operate within the Polaris neutron diffractometer allows for neutron data to be collected over the short time scale of a microwave reaction. The neutron data is recorded with respect to time which can then be split into smaller sections to investigate the reaction pathways in increasingly granular detail. Throughout this project, several binary metal chalcogenide chemical systems known to be thermoelectric materials of interest were investigated. Thermoelectric generators make use of the Seebeck effect to generate useable currents from an applied temperature gradient, allowing waste heat to be converted back into valuable electricity. For each system a range of samples were prepared in which the selenium component was partially substituted with a either tellurium or sulfur in order to hopefully tune the thermoelectric properties. The substitution subprojects enabled a large list of samples to be prepared for synthesis in the Polaris-SMC microwave reactor under well understood reaction conditions. Many of these materials have not been produced previously using a direct microwave heating method in the solid state, and so the insights gained from the in-situ neutron data should help optimisation their synthesis conditions in the future

Tenth European Powder Diffraction Conference – Geneva, September 1-4, 2006

Zeitschrift für Kristallographie. Supplement Volume 26 presents the complete Proceedings of all contributions to the X European Powder Diffraction Conference in Geneva 2006: Method Development and Application, Instrumental Software Development, Materials Supplement Series of Zeitschrift für Kristallographie publishes Proceedings and Abstracts of international conferences on the interdisciplinary field of crystallography

Crystal Cartography: Mapping Nanostructure with Scanning Electron Diffraction

Nanostructure describes the network of defective and distorted atomic structure existing on the nanoscale within materials. This nanostructure bridges the gap between idealised crys- talline structure and real materials, playing a deterministic role in tailoring physico-chemical properties, as well as providing a basis for mechanistic understanding of complex processes such as mechanical deformation and phase transformation. Characterising nanostructure, to develop understanding of materials, requires experimental techniques capable of probing the structure with spatial resolution on the order of nanometres and across regions of interest up to micrometres. Recent developments in electron microscopy, enabling the acquisition of numerous diffraction patterns in a spatially resolved manner, combined with modern computational power, provides a route to meet this need as developed in this work. Scanning electron diffraction (SED) involves the acquisition of a two-dimensional elec- tron diffraction pattern at each probe position in a two-dimensional scan of a specimen. An information rich 4-dimensional (4D-SED) dataset is obtained that can be analysed extensively post-facto using a wide-range of computational methods. The acquisition of such 4D-SED data from the specimen at numerous orientations may also enable the reconstruction of nanostructure in three-dimensions via tomographic methods. In this work, methods for the acquisition and analysis of 4D-SED data are developed and applied to reveal nanostructure in two and three-dimensions. These methods are applied to various prototypical characterisation challenges in materials science, particularly: strain mapping in two and three dimensions, revealing inter-phase crystallographic relationships, mapping grains in two-dimensional materials, and probing nanostructure in polyethylene

Magnetism in the complex cobaltates Y1−xSrxCoO3−δ (0.7 ≤ x ≤ 0.95) and Ca3Co2O6

The magnetic phases in the complex cobaltates Y1−xSrxCoO3−δ (0.7 ≤ x ≤ 0.95) and Ca3Co2O6 have been investigated by susceptibility, heat capacity, X-ray and neutron scattering techniques. These measurements have shown that the super- structure ordering in the perovskite cobaltate Y1−xSrxCoO3−δ which evolves as a function of temperature heavily influences the ferrimagnetic behaviour of this mate- rial. Neutron scattering has also been used to probe the unusual time and magnetic field dependent behaviour of the spin-chain compound Ca3Co2O6, and to further our understanding of the magnetic phase diagram of this system. Both polycrystalline and single crystal samples have been used in this study. High quality single crystals of the A-site (Sr/Y) and oxygen vacancy ordered form of the perovskite Y1−xSrxCoO3−δ have been produced using the floating zone technique and characterised using EDAX and TGA. The single crystals produced were large enough to perform polarised and inelastic neutron scattering experiments on this compound for the first time, revealing anisotropic quasi-elastic scattering above the magnetic transition temperature. In addition, diffraction experiments on these samples found evidence of coincident structural and magnetic transitions in Y1−xSrxCoO3−δ at both 370 and 280 K. Neutron diffraction measurements were also performed on the geometrically frustrated compound Ca3Co2O6. The low temperature magnetisation process was found to be accompanied by clearly visible steps in the intensity of the ferromagnetic and antiferromagnetic Bragg peaks. Detailed measurements have shown that the presence of short-range correlations cannot account for the reduction in intensity of the antiferromagnetic Bragg peaks at low temperatures. Instead, the origin of this drop in intensity was found to be a slow time-dependent magnetic transition from one long-range ordered antiferromagnetic state to another. This transition occurs over a timescale of hours and is never complete. The experimental work detailed in this thesis provides new information about the phase diagrams of Y1−xSrxCoO3−δ and Ca3Co2O6 and contributes to our overall understanding of the physics of these complex cobaltate compounds

Synthesis, structures and properties of inorganic framework materials

Chapter 1 reviews the literature on the structures and properties of inorganic framework materials that are of relevance to this thesis. In particular the phenomenon of negative thermal expansion and the AM(_2)O(_8)/AM(_2)O(_7) families of materials are discussed. Chapter 2 describes the methods of synthesis and characterisation of the materials investigated in this thesis. Chapter 3 discusses the dehydration reaction of M(_o)O(_2).H(_2)O.PO(_3)OH. The study involved the introduction of a new methodology for whole pattern powder fitting; this method was later verified by full Rietveld analysis. This investigation led to the discovery and structure solution of two new molybdenum phosphates using powder XRD. These materials have been named β-(MoO(_2))(_2)P(_2)0(_7) and β -(Mo0(_2))(_2)P(_2)0(_7). A structural pathway for the dehydration reactions has been proposed which is consistent with all of these structures and other analytical data obtained. Chapter 4 describes investigations into the structures of a-(Mo02)2P207 by powder diffraction and NMR methods. The high temperature structure was confirmed to be related to a literature model. The low temperature structure was further studied by electron diffraction, second harmonic generation and solid state NMR. The use of these complementary techniques with powder X-ray and neutron diffraction data, led to the solution of the complex superstructure. Chapter 5 describes a study into the structures of (MoO)(_2)P(_4)0(_13). The material undergoes a phase transition at 523 K. The low temperature structure contains 441 unique atoms and as such is the most crystallographically complex oxide solved to date. The high temperature structure contains 253 unique atoms and is the second most complex oxide in the ICSD. Chapter 6 describes the in-situ X-ray studies on the synthesis of M0P(_2)O(_7) from precursors Mo0(_2)(P0(_3))(_2) and (MoO)(_2)P(_4)0(_13) in an H(_2) environment. (Mo0(_2))(_2)P(_2)0(_7) was studied under similar conditions and found to decompose to an unidentifiable poorly crystalline phase. Chapter 7 describes the discovery of a new high temperature synthetic route to cubic ZrMo(_2)0(_8) using extremely rapid time-resolved XRD data recorded at the ESRF. The cubic material forms from its constituent oxides at 1350 K and can be isolated back at room temperature using a quench cooling method. A pure phase sample can be prepared using a Zr0(_2):Mo0(_3) ratio of 1:3. The entire synthesis occurs within seconds and precise control of temperature and time is crucial for this synthesis