Das Kristallsystem SrxBa1-xNb2O6 wurde über den gesamten Bereich, in dem die tetragonale Phase existiert, gezüchtet und untersucht. Es wurden die Gitterkonstanten, die Dichte, die Brechungsindizes und die Phasenübergangstemperatur bestimmt. Das Phasendiagramm des Kristallsystems wurde neu bestimmt.

No description available.

The Sr/Ca ratios in calcium carbonate fossils are used by the paleooceanographic community to infer past environmental conditions, such as sea surface temperature and ocean chemistry. The processes of biogenic calcification that produce these chemical signatures are complex and not fully understood, however, and vital effects are known to affect the trace element composition of the CaCO₃ biomineral products. The recent discovery that calcifying organisms produce amorphous calcium carbonate (ACC) as an intermediate phase during the crystallization process calls into question whether this pathway to mineral formation affects trace element distributions in the final product. This non-classical mineralization process raises the question of whether the Sr/Ca ratios of the final products are dependent upon temperature. That is, what is the temperature dependence of Sr/Ca ratios in calcite produced via ACC compared to the measurements obtained from calcite grown by the classical process in laboratory experiments and from biogenic settings. The goal of this study is to determine the effects of solution chemistry and temperature on the Sr composition of ACC and resultant crystalline CaCO₃. Two types of experiments were designed: First, experiments were conducted to synthesize inorganic ACC in a batch reactor for a suite of selected chemical compositions and allowing this intermediate phase to transform into calcite in the reactant solution. In a second series of experiments, ACC was precipitated by a flow-through method to compare results to the batch reactor experiments. The experimental design focused on determining the Sr/Ca ratio and Sr distribution coefficients (KD, Sr) of the amorphous and final crystalline products. Mg/Ca ratios of 5/1 were found to suppress Sr uptake into ACC by a factor of 25% when the initial Sr solution had concentration of one millimolar. ICP-AES data collected across the 18° to 30°C range showed that the Sr/Ca ratio in both ACC and the resultant calcite was independent of temperature. Upon transformation, the Sr/Ca ratios of both the ACC and calcite product were found to be similar, showing that Sr/Ca ratios were independent of the transformation process. Analysis of the data determined KD, Sr values of 0.564(±0.006) for ACC and 0.466(±0.009) for the resultant calcite in the 18-30°C temperature range. The findings show that the Sr/Ca ratios of ACC and the transformed calcite are independent of temperature. However, the corresponding KD, Sr values exceed those reported for calcite grown by classical processes by an order of magnitude. The findings for the inorganic calcite yield KD, Sr values up to four times higher than those found in biogenic calcites. Because the findings of this study show that Sr/Ca is independent of temperature, this study calls into question whether previously reported Sr/Ca measurements in biogenic calcites should be revisited. It is plausible that biological factors have a significant influence on trace element incorporation into biogenic calcite. Vital effects, such as the influence of macromolecules during the ion uptake process, may regulate the apparent Sr/Ca versus temperature trends observed in marine paleontology. Higher KD, Sr values in marine calcifiers may indicate that organisms use the non-classical mineralization pathway in whole or in part. Future studies of trace element incorporation in calcifying species should consider the pathway to mineralization in tandem with interpretations of environmental controls on distribution coefficients. / Master of Science

Osteoarthritis is a degenerative joint disease which affects the entire joint; however, one of its hallmarks is the progressive degeneration of the articular cartilage layer. Patients suffering from osteoarthritis exhibit chronic pain, stiffness, and a decreased range of motion, greatly affecting their quality of life. No drugs have been approved to stop the progression of osteoarthritis and focus solely on the management of symptoms. This is partly due to the challenges in delivering drugs to afflicted joints, and specifically to cartilage due to its lack of vasculature. While intra-articular injection holds promise for the local administration of drugs, small molecules are rapidly cleared from the synovial fluid. As a result, there is a need to develop effective drug delivery strategies to improve residence times in the joint to elicit a sustained therapeutic effect. Previous studies identified polyphosphate as a pro-anabolic molecule, promoting glycosaminoglycan and collagen accumulation in cartilage constructs. Therefore, polyphosphate may be a therapeutic of interest to address the degeneration of articular cartilage in patients suffering from osteoarthritis. In this study, calcium-polyphosphate and strontium-polyphosphate particles were synthesized and characterized as a potential drug carrier into articular cartilage. Physicochemical characterization revealed that the particles exhibit a spherical morphology, have a negative zeta potential, and are nanoscale in size. Biological characterization in chondrocytes confirmed cellular uptake of the particles and demonstrated a size and concentration-dependent cytotoxicity at high concentrations. Furthermore, treatment of chondrocytes with these particles resulted in a reduction in metabolic activity and cell proliferation, confirming biological effects. Preliminary studies using cartilage explants suggest that the particles can penetrate and be retained in cartilage tissue. Therefore, from the results obtained within this study, the polyphosphate-based particles may be a potential drug delivery strategy for delivery into articular cartilage.

This dissertation investigates how the magnetic properties of strontium hexaferrite change upon the substitution of foreign atoms at the Fe sites. Strontium hexaferrite, SrFe12O19 is a commonly used hard magnetic material and is produced in large quantities (around 500,000 tons per year). For different applications of strontium hexaferrite, its magnetic properties can be tuned by a proper substitution of the foreign atoms. Experimental screening for a proper substitution is a cost-intensive and time-consuming process, whereas computationally it can be done more efficiently. We used the ‘density functional theory’ a first principles based method to study substituted strontium hexaferrite. The site occupancies of the substituted atoms were estimated by calculating the substitution energies of different configurations. The formation probabilities of configurations were used to calculate the magnetic properties of substituted strontium hexaferrite. In the first study, Al-substituted strontium hexaferrite, SrFe12-xAl x O19, with x = 0.5 and x = 1.0 were investigated. It was found that at the annealing temperature the nonmagnetic Al+3 ions preferentially replace Fe+3 ions from the 12k and 2a sites. We found that the magnetization decreases and the magnetic anisotropy field increases as the fraction, x of the Al atoms increases. In the second study, SrFe12-x Gax O19 and SrFe12-x Inx O19 with x = 0.5 and x = 1.0 were investigated. In the case of SrFe12-x Gax O19, the sites where Ga+3 ions prefer to enter are: 12k, 2a, and 4f1. For SrFe12-x Inx O19, In+3 ions most likely to occupy the 12k, 4f1, and 4f2 sites. In both cases the magnetization was found to decrease slightly as the fraction of substituted atom increases. The magnetic anisotropy field increased for SrFe12-x Gax O19, and decreased for SrFe12-x Inx O19 as the concentration of substituted atoms increased. In the third study, 23 elements (M) were screened for their possible substitution in strontium hexaferrite, SrFe12-x Mx O19 with x = 0.5. In each case the site preference of the substituted atom and the magnetic properties were calculated. We found that Bi, Ge, Sb, Sn, and Sc can effectively increase the magnetization, and Cr, P, Co, Al, Ga, and Ti can increase the anisotropy field when substituted into strontium hexaferrite.

No description available.

No description available.

Barium Strontium Titanate (BST) was deposited on Pt/ZrO2 / SiO2/Si substrates using liquid source metal organic chemical vapor deposition. A stoichiometry series was deposited with various GrII/Ti ratios (0.658 to 1.022) and a temperature series was deposited at 550 to 700°C. The thin films were characterized using transmission electron microscopy. Both series of samples contained cubic perovskite BST and an amorphous phase. The grain size increased and the volume fraction of amorphous phase decreased with increasing deposition temperature. The electrical and microstructural properties improved as the GrII/Ti ratio approached 1 and deteriorated beyond 1. This research demonstrates that BST thin films are a strong candidate for future MOS transistor gate insulator applications.

No description available.

No description available.