Freiberg (Sachsen), Techn. Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Freiberg (Sachsen), Techn. Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Freiberg (Sachsen), Techn. Universiẗat, Diss., 2001.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

The vibrations of H₂O, HDO and D₂O molecules participating in the hydrogen bonding of vitreous and crystalline solids, and some alkyl halides and halogens encaged in these solids, were studied by infrared spectroscopy between 4.2 and 200°K over the 4000 to l60 cm⁻¹ frequency range. Four kinds of 0-H‧‧‧‧0 hydrogen bonding lattices were investigated, vitreous and annealed (cubic) ice I and vitreous and annealed clathrate-hydrate mixtures. In vitreous ice I the effects on the molecular and lattice vibrations were observed in detail for H₂O between 77 and l80°K during the phase transformation to cubic ice I, and the results of the transformation for HDO and D₂O were recorded. As well, the effects on the molecular and lattice vibrations of H₂0, D₂0, H₂0 (5-9W HDO), and D₂0 (4.00% HDO) cubic ices I were studied during warming from 4.2 to 200°K. Similar studies were made for the vibrations of H₂0, HDO, D₂0 and guest molecules, during the vitreous-crystalline phase transformation of seven clathrate-hydrate mixtures and during warming of the resulting annealed mixtures. For ice I the method involved condensation of the vapour at 77°K, observation of the spectra during warming in stages to 185 ± 5°K, cooling to 4.2°K, and observation of the cubic sample spectra during warming to 200°K. The results were plotted as a function of temperature and were correlated to calculated distances and RMS amplitudes of translation. As well four models for molecular libration were investigated. Three approaches were taken to the clathrate-hydrate problem. In parallel to the ice I method gaseous stoichiometric mixtures were condensed, observed during transformation, cooled to 4.2°K and observed during warm-up. Other gaseous clathrate mixtures were condensed in an isolated sample chamber, to prevent sample fractionation, and treated as before. Finally, low temperature mulls of solid clathrate-hydrate mixtures were prepared and observed at 83 ± 3°K. The results show that on warming the ice I phase transformation occurred between 120 ± 5 and 135 ± 5°K and required, less than 18 minutes at 135 ± 3°K. Weak peaks due to oligomeric H₂O and D₂O units disappeared during annealing, while all hydrogen bonded H₂O molecular modes shifted to lower frequency and all lattice modes shifted to higher frequency. The half-height widths of the composite H₂O band (v₂/2vR) appeared to increase upon annealing and to decrease upon warming while the (VR, VR + vT) and (v₁, v₃, v₁ + vT) bands had the opposite behaviour. This was interpreted, as indicating a weak 2vR band underlying the stronger v₂ absorption near 1600 cm⁻¹. The frequency-temperature dependences of all cubic ice I bands were interpreted on a bilinear, high and low temperature basis (the lattice modes shifted to lower frequency and the molecular modes to higher frequency with increasing temperature). For HDO above 86°K [formula omitted] was 0.200 ± 0.005 cm⁻¹/°K, [formula omitted] was 0.123 ± 0.005 cm⁻¹/°K, the frequencies were "frozen-in" at 80 ± 5°K and 65 ± 5°K and had irregular behaviours between 50 and 70°K. The low temperature dependences were 0.047 ± 0.005 cm⁻¹/°K in both modes. An explanation is given for the apparent displacement of the HDO stretching frequencies from the H₂O and D₂O frequencies. The HDO results also permitted the accurate determination of [formula omitted] as 1921 cm⁻¹/Å and [formula omitted] as 128l cm⁻¹/Å above 150°K and as 8202 cm⁻¹/Å and 6629 cm⁻¹/Å below 100°K. As well, the HDO stretching frequencies gave an anharmonicity which increased from 4.2 to 80°K and then decreased between 80 and 200°K. The clathrate-hydrate mixtures transformed on warming in the temperature range 125 ± 5 to 145 ± 5°K and required less than l8 minutes at 135°K as for ice I. Similarly, the weak oligomeric and guest absorptions disappeared upon annealing. From the comparison of the three sets of "clathrate" results and the behaviour of annealed sample peaks we concluded that cubic ice I and not clathrate-hydrate was probably formed. / Science, Faculty of / Chemistry, Department of / Graduate

The Li-Ti-S ternary system was investigated. The elements and/or compounds, such as lithium sulfide, titanium disulfide and titanium trisulfide, were combined at high temperature (typically 500-900°C). The synthesized compounds containing one or more phases were structurally characterized using x-ray powder diffraction. When Lix TiS₂, (0 ≤ x ≤ 1) was synthesized at elevated temperature, a new polytype, 3R-LixTiS₂, was found for some values of x. The regions of stability of the 3R polytype and the well known 1T polytype are presented. Lithium can be intercalated or de-intercalated from both polytypes at room temperature. Ambient temperature Li/3R-LixTiS₂ cells have higher average voltages than Li/1T-Li TiS₂, cells. The lithium spinel oxides are another class of materials receiving attention as cathode materials in lithium secondary batteries. LiTi₂0₄ is metallic, has the cubic spinel structure and reacts with one further lithium atom to form Li₂Ti₂0₄. The related spinel Li₄/₃Ti₅/₃⁰₄͵ which is electrically insulating, also reacts reversibly with one lithium atom. Both Li₂Ti₂0₄ and Li₄/₃Ti₅/₃⁰₄͵ cells cycle reversibly, but have subtle differences in their voltage profiles. The difference in cell behaviour was interpreted based on the band structure of Li₁˖xTi₂₋x⁰₄. The mixed spinels LiMnyTi₂₋y⁰₄ (0 ≤ y ≤ 2) were also investigated. These compounds were synthesized at high temperature but their performance as cathodes in lithium batteries was not encouraging. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Debye-Scherrer x-ray powder photography is used to study the dependence of the host lattice parameters of LixMoCO₂ (0 ≤ x≤ 1) upon the lithium content (x). The results indicate that the host lattice expands considerably as x increases but that the lattice reassumes its original structure when the lithium is removed. Intercalating one equivalent of lithium (x = 1) causes a considerable (~13%) increase in the unit cell volume. This expansion is confined to directions perpendicular to the tunnels through the MoO₂ lattice. Detailed measurements are made of the voltage V(x) of Li/LixMoO₂ cells. These and the x-ray patterns both indicate that LixMoO₂ occurs in three distinct compositional phases with approximate compositions of MoO₂, Li1/2MoO₂ and LiMoO₂. First-order transitions involving pronounced hysteresis effects are observed as the lithium content is altered. A brief discussion of the electrochemical properties of the LixMoO₂ system in terms of a lattice gas model is included. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis identifies and discusses physical mechanisms in intercalation batteries. The effects of interactions and ordering of intercalated atoms on the voltage behaviour of intercalation cells is described, largely in terms of the lattice gas model of intercalation. Particular emphasis is given to the mean field solutions of the lattice gas model, which are compared to more exact solutions for several cases. Two types of interaction between intercalated atoms are discussed, namely electronic and elastic interactions; it is found that both can be important in intercalation compounds. The kinetics of intercalation batteries is also discussed, with emphasis on overpotentials due to diffusion of the intercalated atoms in the host lattice. Experimental studies of the voltage behaviour of three types of lithium intercalation cells, Li[sub=x]TiS₂, Li[sub=x]MoO₂, and Li[sub=x]MoS₂, are presented, which illustrate the variety of voltage behaviour found in intercalation cells. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis describes experimental methods, including in situ X-ray diffraction, especially suited to the study of lithium intercalation systems,and discusses the interpretation of the results obtained in a study of Li[sub=x]TiS₂. A rigid plate and spring model of layered intercalation systems is developed and is used to investigate the role of lattice expansion and elastic energy in layered intercalation compounds. When the elastic energy, calculated using the spring and plate model, is included in the Hamiltonian of a three dimensional lattice gas model for Li[sub=x]TiS₂ good agreement between the experimental results and the theoretical predictions are obtained. Staging, not lithium ordering, is identified as the dominant physical mechanism in Li[sub=x]TiS₂. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Includes bibliographical references. / The synthesis and characterization of a series of inorganic coordination compounds which, upon crystallization, have the ability to include solvent or guest molecules spatially within the lattice are reported. The compounds have the following general formula: [NiX2B4] - where X is isothiocyanate or bromine and B is 4-ethylpyridine, 4-vinylpiridine or 3,5-dimethylpyridine; [NiX2B2]n - where X is isothiocyanate, B is 2-aminopyridine and n indicates it is a polymer; [NiX2AB2]2 - where X is isothiocyanate, B is 3-aminopyridine (two of these four ligands in the dimer are bridging) and A is water. The various guest molecules have been carefully chosen, according to their point symmetry, which is a key factor in yielding structures of a particular type. The structures of seventeen compounds have been elucidated by single crystal x-ray analysis. The difficulty has been found to lie in refining disordered guest molecules. Other techniques employed in the initial characterization of these compounds are Microanalysis, Mass Spectrometry and UV/Visible Spectrophotometry. An intramolecular potential energy study on the [Ni(NCS)2(3,5-diMepy)4] complex reveals that the orthohydrogens on the 3,5-dimethylpyridine ligands control the conformation of the molecule. Packing densities and volume comparisons of the [Ni(NCS)2(4-Etpy)4] and [Ni(NCS)2(4-Vipy)4] complexes and their clathrates have been carried out. The exact sizes and shapes of the cavities in which the guest molecules are located in the x-ray crystal structures have been evaluated by both intermolecular potential energy and molecular volume calculations. Thermodynamic and spectroscopic properties of the [Ni(NCS)2(4-Etpy)4] and [Ni(NCS)2(4-Vipy)4] clathrates have been studied in both solution and the solid state. The techniques used are x-ray powder diffractometry, IR spectroscopy and Thermogravimetry (including Differential Thermal Analysis).