Solid state NMR has the ability to obtain detailed structural information at the molecular level in materials. This has led to the development of a large number of high resolution techniques, some of which utilize multiple pulse methods. The behaviour of these multiple pulse techniques has, to date, been explained using either relaxation or spin dynamics. Ultimately, an explanation based on a combination of both dynamics is required in order to properly understand the underlying mechanism of these techniques. This work presents an explanation of the experimental behaviour observed for three multiple pulse domain selection techniques: the DIVAM, Direct DIVAM, and Refocused DIVAM sequences. This is based on a combination of spin and relaxation dynamics and is accomplished using both analytical expressions and simulations obtained using a general simulation program for solid-state NMR spectroscopy (SIMPSON). / xviii, 179 leaves ; 29 cm

Dielectric, d. c. conductivity and electrolysis measurements have been made principally on solid imidazole and urea. Electrode effects, especially the development of a suitable protode, and techniques for detecting mobile protons in solids were pursued. The dielectric data have been correlated with the d. c. results. A mechanism for extrinsic proton conduction in urea has been proposed.

The solid state and solution phase photochemistry of three bridgehead-substituted dibenzobarrelene-11,12-diesters and a 2,3-naphthobarrelene diester derivative were investigated. These compounds were expected to undergo the di-π-methane rearrangement via their triplet excited states, and a rearrangement to a cyclooctatetraene (COT) derivative via their singlet excited states. All compounds investigated underwent smooth photoreactions in the solid state to produce the same products as observed in the corresponding solution phase photolyses. One exception to this was a bridgehead dimethyl- substituted dibenzobarrelene diester. In this case an unusual photo-product which was characterized as a dibenzopentalene derivative, was obtained in the solid state along with lesser amounts of the normal-solution products. The mechanism proposed for the formation of this product involves a 1,4-biradical intermediate which undergoes a novel double 1,2-ester migration. It was recognized that this biradical intermediate could also undergo fragmentation to produce a cyclooctatetraene (COT) derivative which differs in its symmetry from that of the COT expected based on the mechanism proposed by H. E. Zimmerman for similar transformations observed in the cases of benzo- and naphthobarrelenes. Thus, there are two structures possible for the COT formed which cannot be distinguished based on their spectral properties. For this reason, single crystal X-ray diffraction analysis of the COTs formed in each case was performed. Of the four COT structures determined by X-ray crystallography, three COTs had structures that were consistent with the fragmentation mechanism, while one had a structure consistent with the Zimmerman mechanism. In light of the possible unusual photorearrangements observed, it was thought desirable to establish the molecular structures of all photo-products obtained. To this end, crystal and molecular structures of 11 photoproducts were determined. Also, in an attempt to establish structure-reactivity relationships, crystal and molecular structures of four starting materials were determined. A bridgehead chloromethyl-substituted dibenzobarrelene diester was also found to produce dibenzopenatalene-like photoproducts in the solid state or in chloroform solution; these photoproducts were also characterized based mainly on X-ray crystallography. These results add to the generality of the unusual photobehavior of some dibenzobarrelene derivatives. In the solution phase photolysis of a bridgehead dichloro-substituted dibenzobarrelene diester, a novel cyclic peroxide product was obtained. This was rationalized as being derived from photolysis of the primary di-π-methane photoproduct followed by trapping of the resulting 1,3-biradical by traces of molecular oxygen present in the reaction mixture. Thus, in the present study it was found that bridgehead substituted dibenzobarrelene derivatives undergo di-π-methane rearrangement via their T₁ states as expected, but that their S₁ states may undergo unusual rearrangements to produce cyclooctatetraene derivatives with unexpected structures, and dibenzopentalene derivatives in some cases. / Science, Faculty of / Chemistry, Department of / Graduate

This thesis first uses physical scale models to investigate solid-state phenomena - surface layer formation, solid-state diffusion of lithium, electrochemical reactions at the solid-electrolyte interface, as well as homogeneous chemical phase change reactions. Evidence is provided that surface layer formation on the magnetite, Fe3O4, electrode can accurately be described mathematically as a nucleation and growth process. To emulate the electrochemical results of the LiV3O8 electrode, a novel method is developed to capture the phase change process; this method describes phase change as a nucleation and growth process. The physical parameters of the LiV3O8 electrode: the solid-state diffusion coefficient, phase change saturation concentration, phase reaction rate constant, and exchange current density, are all quantified and the agreement with experimental results is compelling. Electrochemical evidence, corroborated by results from density functional theory, indicate that delithiation is a more facile process than lithiation in the LiV3O8 electrode. Further investigation of the LiV3O8 electrode is undertaken by coupling the crystal scale model to electrode scale phenomena. Characterization of the LiV3O8 electrode by operando EDXRD experiments provides a unique and independent set of observations that validate the previously estimated physical constants for the phase change saturation concentration and phase change reaction rate constant; they are both found to be consistent with their previous estimates. Finally, it is observed that anodic physical phenomena are important during delithiation of the cathode because the kinetics at the anode become mass-transfer limited. Finally, it is illustrated that coupling physical models to data science and algorithmic computing is an effective method to accelerate model development and quantitatively guide the design of experiments.

Ces travaux de thèse portent sur l’étude des propriétés chimiques et physiques de chalcogénures polaires (CPs) à valence normal ou hypervalents. Ces composés appartiennent à la famille des intermétalliques polaires, et s’inscrivent donc dans le champ d’étude de la chimie des intermétalliques. Le but premier de cette étude est la synthèse de nouveaux composés de structure cristalline complexe, afin d’étudier la relation entre la structure cristalline, la nature des liaisons chimiques et les propriétés physiques, déterminées par des mesures expérimentales et des analyses théoriques. Les CPs ont été choisis comme matériaux d’étude car ils se situent à la frontière entre les matériaux métalliques et non-métalliques. Pour ces matériaux (les CPs), les propriétés chimiques sont gouvernées par l’interaction entre les différents types de liaisons – covalente, métallique et ionique – ouvrant la voie à l’étude des liens entre structure cristalline et liaisons chimiques. La recherche de matériaux à structure complexe permet de cibler de potentiels matériaux thermoélectriques prometteurs, puisque la complexité structurale est souvent reliée à une faible conductivité thermique, qui est une propriété clé des thermoélectriques. Les matériaux thermoélectriques transforment la chaleur en électricité, et sont donc au cœur des enjeux économiques et environnementaux actuels. La découverte de thermoélectriques à bon rendement appartenant à la famille des chalcogénures, tels que PbTe, Bi2Te3, CsBi4Te6 et le composé superionique Cu2-xSe ont orienté les recherches vers l’exploration de composés chalcogénures de type Cu- et Pn- (Pn = Sn, Bi), et ont motivé l’étude de matériaux voisins, comme BaBiTe3 (chapitre V). Une des possibilités pour induire des structures complexes est d’obtenir un transfert de charge du cation (Ba, Se) vers une structure anionique, créant ainsi des réseaux covalents anioniques complexes sous forme de chaines ou de couches, qui sont à l’origine de propriétés physiques intéressantes. Une paire d’électrons libres et stéréoactifs peut également augmenter la complexité de la structure, via une distorsion des polyèdres de coordination, ce qui justifie l’étude de matériaux contenant des éléments de type Pn comme Bi ou Sb. L’analyse des propriétés physiques ainsi que l’étude de la structure cristalline et des liaisons chimiques de chalcogénures polaires de structure complexe, certains connus et d’autres découverts au cours de ce travail de thèse, ont résulté en des découvertes prometteuses. / This thesis has its focus on the chemistry and physical properties of normal valence and hypervalent polar chalcogenides (PCs). The motivation for this study lies in the synthesis of new compounds with complex crystal structures. It aims at understanding the relationship between crystal structure, chemical bonding and physical properties through experimental and theoretical analyses. PCs are of special interest since they are at the interface between metals and nonmetals. The chemistry at this interface is governed by the interplay between covalent, metallic and ionic bonding, which makes it interesting and challenging to understand the relationship between crystal structure and chemical bonding. The main reason for aiming at structural complexity is to target new materials with low thermal conductivities – a key requirement for efficient thermoelectric materials. Thermoelectrics are capable of converting waste heat into electricity, which is of considerable economic and environmental interest. Previous discoveries of efficient, chalcogenide-based thermoelectrics such as PbTe, Bi2Te3, CsBi4Te6 and superionic Cu2-xSe motivated the exploratory search for new Cu- and Pn-chalcogenides (Pn = Sb, Bi) and to study related materials such as BaBiTe3 (cf. chapter V). One route towards complex crystal structures is to use a charge transfer from cations such as Sr or Ba to an anionic framework in order to create complex anionic, covalent networks (e.g. channels or layers) which can lead towards interesting physical properties. Stereoactive lone pairs can increase the structural complexity through distortions of the coordination polyhedra, which is one reason for studying systems containing Pn atoms such as Sb and Bi. Probing the physical properties and studying the crystal structure and chemical bonding of both, new and known polar chalcogenides with complex crystal structures resulted in interesting new discoveries, i.e. new compounds and crystal structures as well as unexpected physical properties. The thesis is separated in normal valence compounds, which can be entirely described by classical two-center two-electron (2c-2e) bonds (i.e. where the electrons are fully localized) and those, which contain hypervalent bonds and networks in which the electrons are partially delocalized. It contains four main parts: the study of 1) A0.5CuZrSe3 et ACuYSe3 (A = Sr, Ba) belonging to a family of compounds known as the “1113 family”, 2) Ba2FePnSe5 (Pn = Sb, Bi), 3) Ba4Cu8Se13 and 4) BaBiTe3-xSex (x = 0, 0.05, 1 and 3).

Part I. Reduction of the 1-methylpentacyclo [5.4.0.0²,⁶.0³,¹⁰,0⁵,⁹]undecane-8, 11-dione (9) with solid NaBH₄ resulted in highly stereoselective reduction of both C=O groups in the substrate, thereby affording the corresponding endo-8, endo-11-diol (11a). The configuration of 11a was established unequivocally by converting 11a into the corresponding cyclic thiocarbonate ester, 12. Part II. Z-1,2-Di(1'-adamantyl)ethene (14) was synthesized with a high degree of stereoselectively in four steps (Scheme 9 in Chapter 2). E-1,2-di(1'-adamantyl)ethene (15) was synthesized by iodine promoted isomerization of 14. Both structures were established unequivocally via single-crystal X-ray structural analysis. E-1-(exo-8'-Pentacyclo[5.4.0.0²,⁶.0³,¹⁰,0⁵,⁹]undecyl)-2-phenylethylene (16a) was synthesized, and its structure was established via analysis of its 1H, 13C, and 2D COSY NMR spectra. Part III. Reactions of electrophiles, i.e.,:CCl_2, PhSCl, and Br_2, to Z- and E-1,2-di(1'-adamantyl)ethenes (14 and 15, respectively) are described (Scheme 5, 8, 10, and 13 in Chapter 3). Structures of the corresponding products were established unequivocally via analysis of their respective one- and two-dimensional NMR spectra and/or single-crystal X-ray structural analysis. Part IV. An improved asymmetric synthesis of optically active (S)-4-hydroxy-2-cyclohexenone 1 (64%ee, determined via Mosher's method) has been developed (Scheme 5 in Chapter 4). The key step in this synthesis involves the baker's yeast reduction of 13. The absolute configuration of the major product, (S)-1, was established unequivocally via single-crystal X-ray structural analysis of a precursor. The optical purity of the major product 14a (80%de, 67%ee) was established via careful integration of relevant gated-decoupled 13C NMR spectra.

Three aspects of precipitate growth by a ledge mechanism in a Ni-45wt%Cr alloy were investigated. The strain energy for ledge formation and ledge growth kinetics and the emission of structural defects were studied experimentally during the growth of bcc laths from an fcc matrix. The elastic strain energy of a growth ledge as a function of the ledge location was estimated using an Eshelby-type model. Ledge nucleation is only likely at facet areas where the interaction energy between the ledge and the precipitate is negative. Ledges form with the lowest strain energy on the broad habit plane of coherent precipitates. On a partially coherent lath the strain energy is lowest for a ledge located on the facet perpendicular to the crystallographic invariant line. This situation favors precipitate lengthening in the invariant line direction. Experimental measurement of growth kinetics of the precipitate was made to examine the mechanistic relationship between precipitate growth kinetics and its morphology. TEM was employed to measure overall precipitate growth kinetics as function of time, crystallographic orientations and ledge density. Results show the precipitates widen and thicken by a ledge mechanism following parabolic growth laws. Morphology of precipitates during aging is closely related to the ledge density. Several types of defect emission from partially coherent interphase boundary in the alloy were observed using conventional and in situ hot stage TEM techniques. Prismatic dislocation loops expand and glide off from the precipitate. Perfect a/2 (110)_fcc dislocations glide away from the broad habit plane. Stacking faults emanated from the broad face of the laths were observed during precipitate growth. These defects result in steps in the interface and appear to compensate misfit in the broad face of the lath. / Ph. D.

This thesis is concerned with the study of two families of materials which contain magnetically frustrated triangular lattices. Each material is concerned with a different use; the first, analogues of YMnO₃, is from a family of materials called multiferroics, the second, A₂MCu₃F₁₂ (where A = Rb¹⁺, Cs¹⁺, M = Zr⁴⁺, Sn⁴⁺, Ti⁴⁺, Hf⁴⁺), are materials which are of interest due to their potentially unusual magnetic properties deriving from a highly frustrated Cu²⁺-based kagome lattice. YFeO₃, YbFeO₃ and InFeO₃ have been synthesised as their hexagonal polymorphs. YFeO₃ and YbFeO₃ have been studied in depth by neutron powder diffraction, A.C. impedance spectroscopy, Mössbauer spectroscopy and magnetometry. It was found that YFeO₃ and YbFeO₃ are structurally similar to hexagonal YMnO₃ but there is evidence for a subtle phase separation in each case. Low temperature magnetic properties are also reported, and subtle correlations between the structural, electrical and magnetic properties of these materials have been found. InFeO₃ was found to adopt a higher symmetry and is structurally similar to the high temperature phase of YMnO₃. TbInO₃ and DyInO₃ have also been synthesised and studied at various temperatures. The phase behaviour of TbInO₃ was analysed in detail using neutron powder diffraction and internal structural changes versus temperature were mapped out – there is also evidence for a subtle isosymmetric phase transition. Neither DyInO₃ nor TbInO₃ show long-range magnetic order between 2 and 300 K, or any signs of ferroelectricity at room temperature. The new compounds Cs₂TiCu₃F₁₂ and Rb₂TiCu₃F₁₂ have both been synthesised and shown to be novel kagome lattice based materials. The former shows a transition from rhombohedral to monoclinic symmetry in the powder form and from rhombohedral to a larger rhombohedral unit cell in the single crystal – a particle size based transition pathway is suggested. For Rb₂TiCu₃F₁₂ a complex triclinic unit cell is found, which distorts with lowering temperature. Both materials show magnetic transitions with lowering temperature. The solid solution Cs₂₋ₓRbₓSnCu₃F₁₂ (x = 0, 0.5, 1.0, 1.5, 2.0) was synthesised and investigated crystallographically, demonstrating a range of behaviours. Rb₂SnCu₃F₁₂ displays a rare re-entrant structural phase transition. In contrast, Cs₀.₅Rb₁.₅SnCu₃F₁₂ shows only the first transition found in the Rb⁺ end member. CsRbSnCu₃F₁₂ adopts a lower symmetry at both room temperature and below. Cs₁.₅Rb₀.₅SnCu₃F₁₂ and Cs₂SnCu₃F₁₂ show a rhombohedral - monoclinic transition, which is similar to that found in Cs₂TiCu₃F₁₂.

This thesis presents a study on several series of unconventional Fe-based superconductors; namely, derivatives of NaFeAs and LiFeAs, as well as molecular-intercalated FeSe. Primarily using muon spin rotation (SR), but also x-ray diffraction (XRD) and magnetic susceptibility measurements, the nature of both magnetic and superconducting phases within these systems is studied. Particular attention is focussed on how these states compete or coexist with one another. The aforementioned experimental techniques are first used to explore the phase diagram of NaFe1xCoxAs. This phase diagram includes regions of long-range antiferromagnetism and short-range order, that both coexist with superconductivity. Magnetism is gradually destroyed, primarily through a diminishment of the size of the ordered moment, as superconductivity is enhanced by Co substitution. This interplay is explored in detail. By contrast, superconductivity in LiFeAs cannot be enhanced by transition metal substitution, suggesting that it is intrinsically optimally-doped. I investigate this conclusion by studying the evolution of the penetration depth in superconducting compositions of LiFe1xCoxAs and LiFe1xNixAs, and comparing these data to those from other electron-doped systems. I also study an unusual and emergent magnetic phase in Li1yFe1+yAs. This work suggests that LiFeAs supports a superconducting phase that resembles those in other Fe-pnictides, but is uniquely close to an additional magnetic instability. I then move on to the study of a recently discovered series, based on FeSe intercalated with ammonia and various metals. I study both the penetration depth and the intrinsic magnetic phases in these systems using SR and compare them with other compounds based on FeSe. I find that these intercalated systems support spacially separated regions of dynamic magnetism and superconductivity and I discuss how much these phases depend on the precise chemical details of the intercalated layer. Finally, I return to the experimental study of NaFe1xCoxAs, extending the range of techniques employed by using high-field magnetometry and high-pressure SR. These studies reveal new features of this system that were not accessible using low-field and ambient-pressure methods. In particular, I show that the magnetic moment size in NaFeAs unexpectedly increases with pressure, suggesting that the electronic structure of this compound may be unique amongst known Fe-based superconductors.

The use of in situ X-ray diffraction (XRD) to investigate reactions involving crystalline materials is the focus of the work described in this thesis. The development of procedures for probing chemical reactions in situ, and the application of this technique for studying in detail the mechanisms and kinetics of solid-state processes, is reported. The information in <strong>Chapter One</strong> provides a background to the in situ study of chemical reactions, with specific emphasis on the application of X-ray diffraction. Three distinct families of inorganic materials are introduced, including layered double hydroxides, Aurivillius phases, and metal-organic frameworks, and the relevance of each in contemporary technologies, is discussed. <strong>Chapter Two</strong> incorporates an account of the design, construction, and development of a chemical reaction furnace, the Oxford-Diamond In Situ Cell (ODISC), for the in situ study of solid-state reactions. The capabilities of this apparatus are discussed, including the efficient and controlled heating of samples to temperatures in excess of 1000 °C, optional sample stirring, and successful incorporation of a range of different sample vessels. Details of the implementation and optimisation of this equipment for use at Beamline I12 at the Diamond Light Source are provided. The synthesis and characterisation of a new series of ternary layered double hydroxides (LDHs) with general formula [M_xM’_2–xAl₈(OH)₂₄](NO₃)4•yH₂O (M, M’ = Zn, Ni or Co), is detailed in <strong>Chapter 3</strong>. It was discovered that these materials exhibit finely tuneable cation ratios in the intralayer regions. A study of the intercalation chemistry of this family is reported, including in situ energy-dispersive and angular-dispersive X-ray diffraction experiments. The chapter concludes with details of an in situ XRD investigation into the synthesis of these materials via direct reaction of metal salts with Al(OH)₃, which was observed to proceed in four stages. <strong>Chapter Four</strong> is concerned with the molten salt synthesis and characterisation of novel cation-doped compounds with the Aurivillius structure. The limited extent of substitution on the B-sites of the parent Bi5Ti3FeO15 material was observed to be highly dependent on the nature of the di- or tri-valent substituent. The impact of varying reaction conditions, such as dwell duration and nature of the molten salt, upon pure product formation is described. A comprehensive in situ XRD investigation into the molten salt synthesis of a novel doped Aurivillius phase is detailed in <strong>Chapter Five</strong>. A discussion of the synthesis mechanism, in addition to a description of the role of the molten salt in product formation, is provided. A brief in situ XRD study of the mechanism and kinetics of crystallisation of metal-organic frameworks (MOFs) is detailed in <strong>Chapter Six</strong>. The use of ion-exchanged polymer resin beads to direct the synthesis of MOFs is probed in real time, and the route to formation is compared to that for the conventional solvothermal technique. Experimental procedures pertaining to all of the above chapters are provided in <strong>Chapter Seven</strong>. Supplementary data are included in the <strong>Appendices</strong>.