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This dissertation combines aspects of lasers, nonlinear optics and interferometry to measure the linear optical properties involved in phase matched second harmonic generation, (SHG). A new measuring technique has been developed to rapidly analyze the phase matching performance of potential SHGs. The data taken is in the form of interferograms produced by the self referencing nonlinear Fizeau interferometer (NLF), and correctly predicts when phase matched SHG will occur in the sample wedge. Data extracted from the interferograms produced by the NLF, allows us to predict both phase matching temperatures for noncritically phase matchable crystals and crystal orientation for angle tuned crystals. Phase matching measurements can be made for both Type I and Type II configurations. Phase mismatch measurements were made at the fundamental wavelength of 1.32 (mu)m, for: calcite, lithium niobate, and gadolinium molybdate (GMO). Similar measurements were made at 1.06 (mu)m. for calcite. Phase matched SHG was demonstrated in calcite, lithium niobate and KTP, while phase matching by temperature tuning is ruled out for GMO.

Thesis (MTech (Chemistry))--Cape Peninsula University Of Technology, 2015. / Twelve multicomponent crystals of dicarboxylic acids (succinic, adipic and suberic acid) with derivatives of picoline (4-picoline, 2,4-lutidine, 3,4-lutidine and 3,5-lutidine) were analyzed with the aim of finding correlation between their melting points and crystalline structural features. The solvates of SUC•2,4LUT, SUC•3,4LUT, SUC•3,5LUT and ADP•4PIC are already known structures but were remade for completeness and to obtain their accurate melting temperatures. The acids were selected because of their systematically increasing chain lengths and the selection of the picoline derivatives were based on the systematic variation of the positions of the methyl groups around the pyridine moiety. All the formed multicomponent crystals were analyzed with single crystal X-ray diffraction and parallel to the solution crystallizations, grinding experiments were carried out to prepare the aimed inclusion compounds by using much less of the solvent of crystallization. Thermogravimetry was used to confirm the solvent content of the bulk material and differential scanning calorimetry was applied to obtain information about the melting process, such as the onset and the peak temperature of the melting and the concomitant enthalpy change. The melting temperatures revealed that the inclusion formation significantly decreased the melting points of the staring materials and the melting points of the inclusion compounds for the same acid varied significantly. Hirshfeld surfaces of the base-acid-base moieties and the related fingerprint plots were compared both qualitatively and quantitatively. The melting points of the compounds were plotted against the percentage contribution of the various intermolecular interactions.

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The purpose of this investigation is to make more detailed studies of transformations. Fourteen compounds have been examined by high temperature X-ray diffraction for this purpose. The investigations have been carried out in such a way as to reveal: 1. the existence of transformations, 2. the influence of polarizability on thermal expansion, 3. the anisotropy of expansion, and 4. the discontinuity of thermal expansion.

One of the primary objects of this research was to determine, if possible, the nature of the radiation damage prior to thermal decomposition. The X-ray study has not wholly achieved this although more information has been derived from it than from similar work on AgMnO₄ However, the diffuse reflections obtained do indicate, quite strongly, the creation of point defects during irradiation. This is of value since such assumptions have been made in the explanation of the kinetics of decomposition of a number of irradiated solids (BaN₆,CaN₆). In addition the X-ray work has suggested future research which should produce useful information; namely, a precise study of the diffuse reflections. Another object of the research was to attempt to determine what characteristics, if any, of the kinetics of the decomposition of an unirradiated solid would predetermine a marked irradiation effect. It is obvious that the type of nuclear growth which occurs e.g. branching chain, or power law, does not characterise a substance with regard to a possible irradiation effect . The photosensitivity, or otherwise, also does not determine whether there will be an irradiation effect. However, the one property that the substances which have been studied, have in common, is a polyatomic anion, but here again ammonium dichromate does not show an acceleration of the decomposition after irradiation. Consequently it is considered that it is not possible to say, a priori, whether a solid will undergo an accelerated decomposition after irradiation. Each new solid, unless it belongs to a particular class e.g. the alkaline earth azides , must be considered afresh. Nevertheless it does appear that the irradiation effect can take two forms: - (i) the production of an unstable compound e.g. nickel oxalate, the decomposition of which affects the normal pyrolysis; and (ii) the production of point defects which determine the nature of the subsequent thermal decomposition e.g . CaN₆ . It is possible that the effect requires an interaction of the created point defects with the existing line defects.

Thermal expansion in a crystal may be completely described from a phenomenological point of view by a second rank tensor whose elements are defined by λ_ij=(∂l_ij/∂T)_σ Or ε_ij=(∂e_ij/∂T)_σ Where the l_ij and the e_ij are the elements of the linear Lagrangian and Eulerian strain tensors respectively. These λ_ij and ε_ij have been formulated in terms of crystal cell parameters. For example, for a monoclinic crystal the λ_ij are of the form: λ₁₁(T) = 1/a₀sinβ₀ d[a(T)sinβ(T)]/dT , λ₁₃(T) = ½ (1/a₀sinβ₀ d[a(T)cosβ(T)]/dT - cotβ₀/c₀ dc(T)/dT) , λ₂₂(T) = 1/b₀ db(T)/DT , and λ₃₃(T) = 1/c₀ dc(T)/dT where a₀, b₀, c₀, and β₀ are the crystal’s cell parameters at some reference temperature T₀. By expressing the crystal cell parameters as power series expansions in the temperature, thermal expansion coefficients have been computed for indialite (hexagonal cordierite), emerald and beryl and for the clinopyroxenes: diopside, hedenbergite, jadeite, ureyite, acmite, and spodumene. The extended Grüneisen equation has been used to further examine the nature of the thermal expansion in emerald, beryl, and diopside. The crystal structures of the synthetic clinopyroxenes CaCoSi₂O₆ (cobalt diopside) and CaNiSi₂O₆ (nickel diopside) have also been determined. / Doctor of Philosophy

Two framework oxide materials of the MO��� network type have been synthesized and structurally characterized by synchrotron and X-ray powder diffraction and the Rietveld method in the temperature range 25~500 K. The results show one of them to be a low thermal expansion material. Theoretical studies of negative thermal expansion (NTE) in framework oxides were conducted with two methods, geometrical modeling by Rigid Unit Mode (RUM) method and lattice dynamic calculations by free energy minimization (FEM) method, the results are compared with each other as well as with experimental observations. RUM analysis of all five types of framework oxide structures negates any simple and direct correlation between presence or absence of RUMs in a structure and the sign of its thermal expansion. Instead, results suggest that NTE of a crystalline solid can not be explained by pure geometrical considerations over its structure alone, and for a better understanding of structure-relationship in negative thermal expansion structures, specific interatomic interactions present in each one must be brought in explicitly. FEM calculation of two negative thermal expansion structures indicates on a structure by structure basis NTE could be predicted and understood within the Gruneisen model, which attributes NTE of a structure to special vibration modes in a structure that softens when the lattice shrinks. The soft NTE modes are, however, not necessarily RUM or RUM like vibration motions. / Graduation date: 2003

This research establishes a physics-based life determination model for the second generation single crystal superalloy PWA 1484 experiencing out-of-phase thermomechanical fatigue (TMF). The life model was developed as a result of a combination of critical mechanical tests, dominant damage characterization and utilization of well-established literature. The resulting life model improves life prediction over currently employed methods and provides for extrapolation into yet unutilized operating regimes. Particularly, the proposed deformation model accounts for the materials' coupled fatigue-environment-microstructure response to TMF loading. Because the proposed model is be based upon the underlying deformation physics, the model is robust enough to be easily modified for other single crystal superalloys having similar microstructure. Future use of this model for turbine life estimation calculations would be based upon the actual deformation experienced by the turbine blade, thereby enabling turbine maintenance scheduling based upon on a "retirement for a cause" life management scheme rather than the currently employed "safe-life" calculations. This advancement has the ability to greatly reduce maintenance costs to the turbine end-user since turbine blades would be removed from service for practical and justifiable reasons. Additionally this work will enable a rethinking of the warranty period, thereby decreasing warranty related replacements. Finally, this research provides a more thorough understanding of the deformation mechanisms present in loading situations that combine fatigue-environment-microstructure effects.