Topotactic routes have been used to produce new materials with tunable electronic and magnetic properties. The host materials were the single and triple layered Ruddlesden-Popper compounds, NaLnTiO4 (Ln = La and Gd) and A2La2Ti3O10 (A = Li and K). These compounds consist of [LnTiO4]- and [La2Ti3O10]2-, respectively, perovskite layers interleaved with two alkali metal ion strata. The topotactic routes used in this research were ion exchange and intercalation. Ion exchange was used to replace the cations in the interlayer space with a cationic unit: vanadyl or the transition metal ion, nickel. This ion exchange route opens the structure to further chemistry because each alkali metal ion is replaced by a divalent ion and a vacancy. In these vacancies other atoms can be inserted. Reductive intercalation with alkali metals is of special interest due to their propensity for forming mixed valence compounds. Mixed valency is usually correlated with semiconductive, metallic or superconductive behaviors, and unusual magnetic properties (CMR). Na0.1(VO) Na0.1(VO) 0.45LaTiO4, Na0.05(VO)0.48GdTiO4 and Li0.3Ni0.85La2Ti3O10 have been obtained by ion exchange reactions. Also, the reactivity of Na0.05(VO)0.48GdTiO4, (VO) La2Ti3O10 and Li0.3Ni0.85La2Ti3O10 is probed by an intercalation reaction with n-BuLi. Lithium insertion between the perovskite blocks reduces the titanium in the perovskite sheets and produces new mixed valence titanates. Lithium intercalation in the vanadyl compounds, Na0.05(VO)0.48GdTiO4 , as well as (VO)La2Ti3O10 gives rise to new magnetic properties. The crystal structures, thermal behavior, electronic and magnetic properties of these new compounds will be discussed.

Iron carbides are amongst the crystalline phases formed during Fischer-Tropsch synthesis to produce hydrocarbons (Dry, 1990, Niemantsverdriet et al., 1980), using iron catalysts. The small crystallite size of the iron carbides causes peak broadening in XRD and prevented complete structure determinations in the past (Hagg, 1931; Retief, 1999; Senateur et al., 1962). Fortunately new instrumentation and techniques, such as fast powder X-ray diffractometers and software for structure determination, are now available to study crystal structures. Five different iron carbide phases are known to form during Fischer-Tropsch synthesis i.e. Hägg carbide (χ-Fe5C2), pseudo-hexagonal iron carbide (έ- Fe2.2C), hexagonal iron carbide (ε-Fe3C), Eckström-Adcock iron carbide (Fe7C3) and cementite (θ-Fe3C). Since the structure of cementite θ-Fe3C is well-known (Westgren & Phragmen, 1922) this study focused on the remainder, i.e. the determination of the crystal structures of the first four iron carbides: Hägg carbide (χ-Fe5C2), pseudo-hexagonal iron carbide (έ -Fe2.2C), hexagonal iron carbide (ε-Fe3C) and Eckström-Adcock iron carbide (Fe7C3). This study consisted of the preparation of iron carbides, structure determinations of these iron carbides, determination of reactions of the iron carbides during Fischer-Tropsch synthesis (FTS) (in situ XRD) and the stability of Hägg carbide (χ-Fe5C2) during FTS under commercial fixed bed reactor conditions. Time-temperature-transformation graphs were determined for iron catalysts with and without potassium promoter. The first step in the structure determination process was the preparation of almost pure samples. Samples of Hagg carbide (:t-FesC2), pseudo-hexagonal 8 -Fe22C iron carbide and hexagonal 1::-Fe3C iron carbide were prepared as pure as possible using the Anton Paar XRK600 reaction chamber attached to an X'Pert Pro multi-purpose diffractometer (N!PD). Eckstrom-Adcock iron carbide (Fe7C3) was available in spent catalyst from a fluidized-bed hydrocarbon synthesis plant at SASOL. These samples were characterized using room temperature and low temperature (77 K) Moss bauer absorption spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM, Philips CM200). Thermo-gravimetric analysis and conductivity measurements were done to characterize the carbonaceous species in the samples. Molecular modelling calculations were done using CASTEP (N!ilman et al., 2000; Payne et al., 1992) to determine the total lattice energies of the iron carbide structures.... / Prof. G.J. Kruger Prof. J.P.R. de Villiers

<p> The crystal structures of three complexes of rhenium have been determined by single crystal x-ray diffraction methods. The structure and the probable position of the hydrogen atom in the complex tetracarbonyl-rhenium(I)-μ-oxo-μ-hydroxotetracarbonylrhenate(I) are discussed.</p> <p> The structural results for the other two complexes show the presence of carboxylato-bridged dinuclear rhenium core. The very short rhenium to rhenium distances and the eclipsed rotomeric configurations are similar to those found in octachlorodirhenate(III) anion. A reaction scheme for the formation of these complexes from rhenium(III) chloride is postulated and correlated with the structural results. The nature of bonding in the carboxylato complexes of rhenium is discussed.</p> / Thesis / Doctor of Philosophy (PhD)

<p> The crystal structures of five ternary oxides and fluorides have been determined. It is shown that the gross features of these structures and the coordination of the atoms can be described in terms of the theory of close-packing of spheres. However, in each of the structures there appear cations whose coordination cannot be uniquely predicted, as the cation-anion radius ratios are close to the critical value for transition from one coordination to another.</p> / Thesis / Doctor of Philosophy (PhD)

Research into conductive organic and organometallic polymers began in 1977 when Heeger, Macdiarmid, and Shirakawa first doped polyacteylene with Iodine. They found that this doping granted the polymer metallic properties increasing conductivity by 11 orders of magnitude.[1] Unfortunately, polyacteylene is highly air-sensitive making it difficult to work with and limiting its applications. Therefore, current research is focused on synthesizing new organic and organometallic conductive polymers. The drive to discover these new polymers stems from their application flexibility and their low production cost. Reported here is the synthesis of novel organometallic polymer precursors. Lead by Dr. Chad Snyder a library of chloro-phenyl based fulvenes, 5,6 fused ring pyridazines, and thallium Cp salts have successfully been synthesized. Research is currently underway to synthesize rhenium and manganese pyridazines through transmetalation of the thallium salts. The off-metal route of synthesis was followed as opposed to the previously reported on-metal route. Characterization was performed by 1H-NMR, 13CNMR, and IR. Additionally, research has begun on bromo-thiophene complexes. So far, bromothiophene fulvenes, pyridazines, and thallium Cp salts have been synthesized and work is currently underway to produced rhenium and manganese pyridazines as well. Characterization was performed by 1H-NMR and 13C-NMR.

The magnetocaloric and thermomagnetic properties of the Ni1-xCrxMnGe1.05 (for x = 0, 0.035, 0.070, 0.105, 0.110, 0.115, and 0.120) system have been studied by X-ray diffraction, differential scanning calorimetry (DSC), resistivity and magnetization measurements. A change in crystal structure from orthorhombic to hexagonal was observed in the XRD data with an increase in chromium concentrations. The values of the cell parameters and volume of the unit cell for hexagonal phase were determined. It was found that the partial substitution of Cr for Ni in Ni1-xCrxMnGe1.05 results in a first order magnetostructural transition from antiferromagnetic to ferromagnetic (FM) at TM of about132 K, 100 K, and 110 K for x= 0.105, 0.115, and 0.120, respectively. A FM to paramagnetic second order transition has been observed at TC around 200K. A magnetic entropy change of = 4.5 J/kg K, 5.6 J/Kg K, and 5.06 J/Kg K was observed in the vicinity of TC for x = 0.105, 0.115, and 0.120 respectively at ΔH = 5T. The values of the latent heat and corresponding total entropy changes have been determined from Differential Scanning Calorimetry (DSC) measurements. Magnetoresistance values of about -5% were measured near TC for x =0.105. The maximum value of refrigeration capacity (RC) and relative cooling power (RCP) was found to be 155 J/Kg and 175 J/Kg respectively for x = 0.120. A concentration-dependent (T-x) phase diagram of transition temperatures has been constructed using the magnetic and DSC data. The structural, magnetic and magnetocaloric properties of GdNi2Mnx system (for x = 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.5) have been studied by x-ray diffraction and magnetization measurements. A mixture of the Laves phase C15 and a phase with rhombohedral structure PuNi3- type (space group R m) was observed in the XRD data. A second order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) was found, characterized by a long-range exchange interaction as predicted by mean field theory. The maximum value of magnetic entropy changes, -∆SM, near TC for ∆H = 5T, was found to be 3.1 J/KgK, 2.8 J/KgK, 2.9 J/KgK, and 2.5 J/Kg K for x = 0.8, 1.2, 1.4, and 1.5 respectively. In spite of the low values of ΔSM, the RC and RCP value was found to be 176 J/Kg and 220 J/Kg for the GdNi2Mn0.8 compound, respectively.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23023号 / 理博第4700号 / 新制||理||1674(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 島川 祐一, 教授 寺西 利治, 教授 長谷川 健 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

<p> The ternary oxide system NiO - Ga2O3 - SiO2 has been studied in the temperature range 1400-1550°C at room pressure. Three phases, corresponding to the spinelloid phases I, II, and V, have been identified on the Ni2GaO4 (spinel) - Ni2SiO4 (olivine) join. These room-pressure phases are isostructural with the high-pressure spinelloid phases of the nickel aluminosilicate system. Single crystals of all three phases have been grown from a silica-rich melt and their crystal structures have been determined by X-ray diffraction. The structure refinements have revealed a strong ordering of the Ga and Si atoms on the tetrahedral sites of all three phases, as well as a clear correlation between spinelloid structure-type and composition. This correlation accounts for the increase in Ni2SiO4 content across the series spinel - phase V - phase I - phase II.</p> / Thesis / Master of Science (MSc)

No description available.

Yes / Tailoring the physical properties of molecular crystals though the construction of solid solutions requires the existence of isostructural crystals. Simple substitutions of a given molecular framework can give a range of different crystal structures. A set of quinoxaline derivatives, C8H4N2(C6H4X)2,Q3,3′X2, has been investigated (X = F, Cl, Br, I and Me) where kinetic factors generated a set of isostructural crystals for the lighter halogens (F, Cl, Br) alone. Computational analysis shows that the stabilising interactions are maximal for Cl, while DSC studies demonstrate the existence of more stable polymorphs for both F and Br containing systems. Steric factors appear to have a lower contribution than the balance of weaker hydrogen and halogen bonding shown by the Me and I containing systems displaying different packing driven by CH⋯N/CH⋯π bonds and I⋯I bonds respectively.