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Doctor of Philosophy(PhD) / This project focuses on the examination of the structures of lanthanide containing double perovskites of the type Ba2LnB'O6-d (Ln = lanthanide or Y3+ and B' = Nb5+, Ta5+, Sb5+ and/or Sn4+) using synchrotron X-ray and neutron powder diffraction. The first part of this project examined the relative stability of R3 rhombohedral and I4/m tetragonal structures as the intermediate phase adopted by the series Ba2LnB'O6 (Ln = lanthanide (III) or Y3+ and B' = Nb5+, Ta5+ or Sb5+). It was found that I4/m tetragonal symmetry was favoured when B' was a transition metal with a small number of d electrons, such as Nb5+ or Ta5+. This is due to the presence of p-bonding in these compounds. In the Ba2LnNbO6 and Ba2LnTaO6 series R3 rhombohedral symmetry was, however, favoured over I4/m tetragonal symmetry when Ln = La3+ or Pr3+ due to the larger ionic radius of these cations. The incompatibility of the d0 and d10 B'-site cations in this family of compounds was indicated by significant regions of phase segregation in the two series Ba2Eu1-xPrxNb1-xSbxO6 and Ba2NdNb1-xSbxO6. In the second part of this project the compounds in the series Ba2LnSnxB'1-xO6-d (Ln = Pr, Nd or Tb and B' = Nb5+ or Sb5+) were examined to understand the relative stability of oxygen vacancies in these materials compared to the oxidation of the lanthanide cations and to determine if any oxygen vacancy ordering occurred. It was found, using a combination of structural characterisation, X ray Absorption Near Edge Structure and Ultra-Violet, Visible and Near Infrared spectroscopies, that with Ln = Pr or Tb increased Sn4+ doping results in a change in the oxidation state of the Ln3+ cations to Ln4+. This leads to those series containing little or no oxygen vacancies. A loss of B site cation ordering was found to accompany this oxidation state change and phase segregation was found to occur in the Ba2PrSnxSb1-xO6-d series most likely due to the Pr3+ and Pr4+ cations segregating into different phases. The Nd3+ cations in the series Ba2NdSnxSb1-xO6-d, however, can not oxidise to the tetravalent state so the number of oxygen vacancies rises with increasing x. It was found that oxygen vacancies concentrate onto the axial site of the compounds with x = 0.6 and 0.8 at ambient temperature. In Ba2Sn0.6Sb0.4O5.7 the oxygen vacancies were found to change to concentrating on the equatorial site at higher temperatures and it is suggested that this oxygen vacancy ordering plays a role in the adoption of I2/m monoclinic symmetry.

Thesis (M. Sc.)--Carleton University, 2008. / Includes bibliographical references (p. 74-88). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [219]-234).

The structure, magnetic behaviour and chemistry of layered oxychalcogenides of composition A₂MO₂X₂Ch₂ (where A = Sr, Ba; M = Mn, Co, Ni, Cu, Zn; X = Cu, Ag and Ch = S, Se, Te) has been investigated by the synthesis of new compounds of this type and control of the properties of these compounds by oxidative deintercalation of Cu/Ag. I₂ can be used to oxidatively deintercalate Cu from Sr₂MnO₂Cu_1.5S₂, forming Sr₂MnO₂Cu_1.33S₂, an incommensurately modulated compound, with a completely different Cu/vacancy ordering and antiferromagnetic ordering structure to the parent. This reaction is also probed in real-time, using in situ powder X-ray diffraction. Sr₂MnO₂Ag_1.5Se₂ was found to have an A-type magnetic ordering structure, similar to Sr₂MnO₂Cu_1.5Se₂. Sr₂MnO₂Cu_1.8Te₂ on the other hand with a lower Mn oxidation state shows only two-dimensional magnetic correlations, rather than long-range order. Extending the reaction with I₂ to several Co-containing analogues revealed that ~ 25% Ag could be removed from Sr₂CoO₂Ag₂Se₂, sufficient to observe a change in magnetic behaviour, from antiferromagnetic to ferromagnetic. By contrast only ~11% Cu can be deintercalated from Sr₂CoO₂Cu₂S₂ and even less (~5%) from Sr₂CoO₂Cu₂Se₂. Neutron diffraction was used to examine the resultant changes in magnetic ordering. The novel compounds Sr₂CuO₂Cu₂Se₂ and Ba₂CuO_2-xCu₂Se₂ are related by substitution of the alkali-earth metal, but while Sr₂CuO₂Cu₂Se₂ is a stoichiometric compound with metal-like character, Ba₂CuO_2-xCu₂Se₂ is an oxygen-deficient semiconductor, with tuneable oxygen content. Unusual features are observed in the magnetic susceptibility measurements of Sr₂NiO₂Cu₂Se₂ that appear unrelated to this compound's long-range magnetic ordering, as probed by neutron diffraction. Furthermore, unusual peak splitting is observed in low-temperature powder X-ray diffraction patterns of this compound; this may plausibly be due to a photon-induced effect arising from the use of a high-energy beamline; although further measurements are required to examine this. Overall the work shows the flexibility and range of behaviour exhibited by a series of the transition metal oxide chalcogenides.

Chan, Mui. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references. / Abstract also in Chinese. / Abstract --- p.i / Abstract (Chinese) --- p.iii / Declaration --- p.v / Acknowledgement --- p.vi / Table of Contents --- p.viii / List of Tables --- p.xiv / List of Figures --- p.xv / Chapter Chapter 1: --- Introduction / Chapter 1.1 --- Overview --- p.1 / Chapter 1.2 --- Soft-Chemistry --- p.7 / Chapter 1.2.1 --- Sol-Gel Method --- p.7 / Chapter 1.2.2 --- Co-precipitation --- p.9 / Chapter 1.2.3 --- Microemulsion --- p.10 / Chapter 1.3 --- Application of Hydrothermal/Solvothermal Methods in Materials Synthesis --- p.12 / Chapter 1.3.1 --- Fundamentals of Hydrothermal and Solvothermal Methods --- p.12 / Chapter 1.3.2 --- Advantages of Hydrothermal/Solvothermal Methods in contrast to Conventional Synthetic Approaches --- p.13 / Chapter 1.3.3 --- Hydrothermal and Solvothermal Preparation of Materials --- p.14 / Chapter 1.4 --- Application of Transition Metal Oxides As Functional Materials --- p.15 / Chapter 1.5 --- Aim and Scope of Work --- p.16 / Chapter 1.6 --- References --- p.17 / Chapter Chapter 2: --- Solvothermal and Hydrothermal Template Free Synthesis of ZnO Microspheres / Chapter 2.1 --- Introduction --- p.23 / Chapter 2.2 --- Experimental Section --- p.25 / Chapter 2.2.1 --- Synthesis of ZnO Microspheres by Solvothermal Method --- p.25 / Chapter 2.2.2 --- Synthesis of ZnO Microspheres by Hydrothermal Method --- p.26 / Chapter 2.2.3 --- Doping ZnO Microspheres with Silver or Gallium by Solvothermal Method --- p.26 / Chapter 2.2.4 --- Characterization --- p.27 / Chapter 2.2.5 --- Measurement of Photocatalytic Activity --- p.29 / Chapter 2.3 --- Results and Discussion --- p.30 / Chapter 2.3.1 --- X-Ray Diffraction Analysis --- p.30 / Chapter 2.3.1.1 --- ZnO-HT and ZnO-ST --- p.30 / Chapter 2.3.1.2 --- ZnO-ST: Effect of Different Concentrations of Zinc Acetate --- p.33 / Chapter 2.3.1.3 --- Doping ZnO-ST with Silver or Gallium --- p.34 / Chapter 2.3.2 --- SEM study --- p.36 / Chapter 2.3.2.1 --- ZnO-HT and ZnO-ST --- p.36 / Chapter 2.3.2.2 --- ZnO-HT-Different Volume Ratios of Ethylene Glycol to Water --- p.37 / Chapter 2.3.2.3 --- ZnO-ST --- p.39 / Chapter 2.3.2.3.1 --- Different Volume Ratios of Benzyl Alcohol to Ethylene Glycol --- p.40 / Chapter 2.3.2.3.2 --- Different Concentrations of Zinc Acetate --- p.41 / Chapter 2.3.2.3.3 --- Different Concentrations of Urea --- p.42 / Chapter 2.3.3 --- TEM Study --- p.44 / Chapter 2.3.3.1 --- TEM and HRTEM of ZnO-HT --- p.44 / Chapter 2.3.3.2 --- TEM and HRTEM of ZnO-ST --- p.45 / Chapter 2.3.3.3 --- TEM Images of Ga-Doped ZnO-ST --- p.47 / Chapter 2.3.3.4 --- TEM Images of Ag-Doped ZnO-ST --- p.49 / Chapter 2.3.4 --- Nitrogen Adsorption and Desorption --- p.50 / Chapter 2.3.5 --- X-Ray Photoelectron Spectroscopy --- p.52 / Chapter 2.3.5.1 --- XPS Study of ZnO-ST --- p.52 / Chapter 2.3.5.2 --- XPS Study of ZnO-HT --- p.54 / Chapter 2.3.5.3 --- XPS Study of Silver Doped ZnO-ST --- p.56 / Chapter 2.3.5.4 --- XPS Study of Gallium Doped ZnO-ST --- p.58 / Chapter 2.3.6 --- FR-IR Spectra --- p.60 / Chapter 2.3.7 --- Photocatalytic Activity on Degradation of Methylene Blue --- p.61 / Chapter 2.3.8 --- Proposed Formation Mechanism for ZnO-ST --- p.64 / Chapter 2.3.9 --- Proposed Formation Mechanism for ZnO-HT --- p.68 / Chapter 2.3.10 --- Optical Property of ZnO Microspheres --- p.69 / Chapter 2.4 --- Conclusion --- p.73 / Chapter 2.5 --- References --- p.74 / Chapter Chapter 3: --- Synthesis of Hierarchical Porous Lithium Niobate Submicrometer Rods / Chapter 3.1 --- Introduction --- p.79 / Chapter 3.2 --- Experimental Section --- p.81 / Chapter 3.2.1 --- Characterization --- p.82 / Chapter 3.3 --- Results and Discussion --- p.83 / Chapter 3.3.1 --- X-Ray Diffraction Analysis --- p.83 / Chapter 3.3.2 --- SEM Study --- p.86 / Chapter 3.3.2.1 --- Surfactants Dependent Morphologies Change --- p.86 / Chapter 3.3.2.2 --- Concentrations of CTAB --- p.87 / Chapter 3.3.2.3 --- Time Dependent Morphologies Change --- p.88 / Chapter 3.3.3 --- TEM Study --- p.91 / Chapter 3.3.5 --- XPS Analysis --- p.93 / Chapter 3.3.6 --- BET Analysis --- p.96 / Chapter 3.3.7 --- Proposed Formation Mechanism --- p.97 / Chapter 3.3.7.1 --- Effect of Microemulsion --- p.97 / Chapter 3.3.7.2 --- Effect of CTAB --- p.98 / Chapter 3.3.7.3 --- Ostwald Ripening --- p.99 / Chapter 3.3.7.4 --- Formation of LiNi3O8 --- p.101 / Chapter 3.4 --- Conclusion --- p.102 / Chapter 3.5 --- References --- p.103 / Chapter Chapter 4: --- Flower-Like α-Nickel Hydroxide synthesized by hydrothermal method / Chapter 4.1 --- Introduction --- p.106 / Chapter 4.2 --- Experimental Section --- p.108 / Chapter 4.2.1 --- Synthesis of Nickel Hydroxide by Hydrothermal Method --- p.108 / Chapter 4.2.2 --- Characterization --- p.109 / Chapter 4.3 --- Results and Discussion --- p.111 / Chapter 4.3.1 --- X-Ray Diffraction Analysis --- p.111 / Chapter 4.3.2 --- SEM Study --- p.115 / Chapter 4.3.3 --- TEM and HRTEM Study --- p.116 / Chapter 4.3.4 --- XPS Analysis --- p.117 / Chapter 4.3.5 --- FT-IR Analysis --- p.119 / Chapter 4.3.6 --- BET analysis --- p.120 / Chapter 4.3.7 --- Proposed Formation Mechanism of the Flower like α-Ni(OH)2 --- p.122 / Chapter 4.4 --- Conclusion --- p.123 / Chapter 4.5 --- References --- p.124 / Chapter Chapter 5: --- Conclusions and Future Work / Chapter 5.1 --- Conclusions --- p.127 / Chapter 5.2 --- Future work --- p.129

Les phases MAX forment une famille de carbures et de nitrures nano-lamellaires de formule chimique Mn+1AXn, où M est un métal de transition des premières colonnes, A appartient aux colonnes 13-16 et X est soit C, soit N, ou une combinaison des deux éléments. Ces phases combinent les mérites des céramiques et des métaux, comme une bonne stabilité chimique, l’usinabilité, la résistance aux chocs mécaniques, de bonnes conductivités thermique et électrique, etc. Malgré tout, l’étude de leurs propriétés intrinsèques et de leurs anisotropies a été jusqu’à présent limitée par l’indisponibilité de monocristaux. Cette thèse traite de la réactivité de tels monocristaux de phases MAX. Grâce à la large taille des cristaux produits au LMGP, il a été possible d’évaluer directement l’anisotropie de la réactivité chimique et d’obtenir des données originales. Nous avons montré le rôle prépondérant joué par l’élément A pour initier des transformations chimiques menant parfois à la synthèse de matériaux originaux, et nous nous sommes concentrés sur quatre aspects différents : Tout d’abord, nous avons tenté de synthétiser des MXènes de grande taille, en profitant de la grande taille des cristaux disponibles. Un effort particulier a été porté sur la description de la réactivité chimique de phases MAX plongées dans diverses solutions d’attaque, avec un accent particulier mis sur l’utilisation de HF. En second lieu, nous avons étudié la chloruration de phases MAX : l’objectif initial était de former des MXènes, mais nous avons finalement développé une méthode pour synthétiser des carbures de chrome poreux avec des propriétés intéressantes. Troisièmement, nous avons utilisé des cristaux de grande taille pour évaluer l’anisotropie des propriétés électrochimiques. Une anisotropie significative a été trouvée, soit en mesurant le courant durant la polarisation électrochimique, soit par mesure de spectroscopie d’impédance. Divers mécanismes ont été proposés afin d’expliquer cette anisotropie des propriétés de corrosion. Enfin, nous avons montré que les résultats électrochimiques pouvaient être utilisés pour révéler indirectement la présence de défauts structurels récemment identifiés dans la littérature. De tels défauts, appelés « ripplocations », sont spécifiques aux matériaux nano-lamellaires. / MAX phases are a family of layered ternary carbides and nitrides with chemical formula Mn+1AXn, where M is an early transition element, A is an element of groups 13 to16 and X is either C, N or both. These phases combine the merits of ceramics and metals, such as chemical stability, machinability, shock resistance, good electrical and thermal conductivity, etc. However, the investigation of their intrinsic properties and anisotropies has heretofore been limited by a lack of availability of single crystals. This thesis mainly deals with the chemical reactivity of MAX phase single crystals. Owing to the large size single crystals grown at LMGP, it was possible to directly assess the anisotropy of the chemical reactivity and to obtain original data. We showed that the prominent role played by the A element for initiating chemical transformations could lead to the synthesis of original materials, and we focused on four different aspects. First, we tried to synthesize MXenes from MAX phase single crystals: The purpose was to obtain large-scale MXenes by taking advantage of the large size of the single crystals. Effort was put on describing the chemical reactivity of MAX phases dipped in different etchants, focusing on HF. Secondly, we studied the MAX phase reactivity with chlorination: the initial purpose was to obtain MXenes, but we finally developed a method for synthesizing porous chromium carbides which exhibit several interesting properties. Thirdly, we used large size single crystals in order to assess the anisotropy of the electrochemical properties. A significant anisotropy was found, either by measuring the current during electrochemical polarization or by frequency-dependent impedance measurements. Several mechanisms were proposed in order to explain this anisotropy of the corrosion properties. Eventually, we showed that the electrochemical results could be used to indirectly evidence the presence of structural defects recently identified in the literature. Such defects, called ripplocations, are specific to nano-lamellar materials.

Solid-state NMR (ssNMR) has matured into a versatile method to provide structural information, probe protein dynamics and detect small molecule binding and -protein interaction of a variety of biomolecular assemblies including amyloid fibrils, viral particles and membrane proteins. Membrane proteins embedded in liposomes are natural targets for ssNMR as their native states are solids. Magic angle spinning (MAS) ssNMR studies using moderate spinning frequencies provide detailed structural information and probe subtle conformational change. Development of fast magic angle spinning ssNMR enables proton-detection which increases sensitivity and facilitates protein dynamics measurements. In this dissertation, we applied moderate and fast MAS ssNMR to study potassium ion channel and protein dynamics Chapter 1 will introduce concepts and theory of solid-state NMR pulse sequences and experiments. Chapter 2 will discuss the application and perspectives of solid-state NMR to membrane protein systems. In Chapter 3, we test an allostery mechanism for inactivation using a KcsA mutant (H25R/E118A) that exhibits an open pH gate across a broad range of pH values. We present solid-state NMR measurements of this open mutant at neutral pH to probe the affinity for potassium at the selectivity filter. This result strongly supports our assertion that the open pH gate allosterically affects the potassium binding affinity of the selectivity filter. In this mutant the protonation state of a glutamate residue (E120) in the pH sensor is sensitive to potassium binding, suggesting that this mutant also has flexibility in the activation gate and is subject to transmembrane allostery. In Chapter 4, I optimize protein expression, purification and reconstitution into native environment protocols of a bacterial potassium transporter, KtrB. In chapter 5, methods and experimental details of setting up 60 and 40 kHz fast MAS ssNMR are discussed. With fast MAS ssNMR setup, multidimensional NMR experiments with higher sensitivity could be collected on a perdeuterated sample with less sample mass required. In Chapter 6, we employ fast MAS ssNMR to measure bulk and residue site-specific 15N and carbonyl 13C relaxation of microcrystalline ubiquitin. Carbonyl R1ρ relaxation profiles provide additional information on protein backbone dynamics.

No description available.