This thesis attempts to test the effects of barium non stoichiometry and varying calcination temperatures on the microstructure and electrical conductivity of BaxZr0.7Pr0.1Y0.2O3- δ (x = 0.9, 1.0, 1.1). BZPY powders were fabricated using a combustion method, with the quantity of barium carefully controlled to create powders with a 10% molar excess or deficiency of barium. Then, portions of the precursor were calcined at 900 ºC, 1000 ºC, 1100 ºC, 1200 ºC and 1300 ºC for 5 h. The resulting calcined powders were pressed into pellets and sintered at 1600 ºC for 10 h, in a powder bath of the same chemical composition. In all, three chemically different powders were synthesized, and each composition was subjected to five different calcination temperatures, resulting in fifteen different samples to characterise. The precursor from the combustion method was characterised by using an STA to perform both TG and DSC simultaneously. The chemical composition of the precursor and calcined samples was analysed using ICP-OES. XRD was used to characterise the phases of both the powders and the sintered pellets. Lattice parameter indexing using Topaz and Scherrer's equation were used to extract the lattice parameters and crystallite sizes respectively. The microstructure of the pellets was examined using an SEM, the grain size measured using a linear intercept method and pore size using ImageJ. Finally, EIS was used to measure the conductivity of the pellets in dry and wet Argon atmospheres, with silver electrodes. Unfortunately, neither changes to barium stoichiometry nor partial calcination could improve the performance of BZPY. Partially calcined samples did not give rise to dense pellets, barium deficient samples showed inferior conductivity and barium excess samples, while showing higher conductivity than the barium deficient pellets at high temperature, were fragile and had to be handled carefully. Ultimately, the attempt to improve the performance of BZPY did not succeed and alternate methods of improving the grain growth need to be sought.

Des simulations numériques conduites sur un ferroélectrique, le Titanate de Baryum, permettent d'extraire les températures où se produisent les transitions pour chacune des composantes et elles utilisent le plus souvent des conditions limites périodiques. Cependant, il est possible de modifier la simulation de manière à rendre compte d'une particule isolée, et les conditions limites électriques de type court-circuit ou bien circuit ouvert affectent alors le résultat. Réduire la taille accorde encore davantage d'importance à de tels effets de surface par rapport aux effets de volume. Expérimentalement, la formation de nanocubes creux ou de nanotores a été observéelors de synthèses solvothermales. De possibles mécanismes de morphogénèse sont évoqués. Dans ce travail, les simulations ont ensuite été conduites sur des particules nanométriques, dont les formes avaient été obtenues expérimentalement. Pour des cubes creux, il a été constaté que la taille de l'inclusion vide modifiait la valeur du coefficient d'écrantage critique à partir duquel le comportement de la polarisation passe d'une configuration de type court-circuit à une configuration de type circuit fermé. Pour des nanotores aux basses températures, une modification du rapport entre petit et grand rayon donne lieu à des configurations possédant un moment toroïdal seul ou accompagné d'un moment hypertoroïdal voire d'oscillations de ce dernier. / Numerical simulations performed on a ferroelectric, Barium Titanate, yield all the transition temperatures under periodic boundary conditions. However, the same simulation can be modified to model an isolated particle under short-circuit or opencircuit electrical boundary conditions. Reducing size makes these surface effects even more important with regard to volume effects.From an experimental point of view, solvothermal synthesis of hollow nanocubesand nanotori is reported and various morphogenesis mechanisms are listed.In this work, simulations were performed on nanometric particles that had experimentally obtained shapes. In hollow cubes, it was shownthat the hole size changed the numerical value of the critical screening coefficient at which the system changes its behavior from aconfiguration that is short-circuit like to another one that is open-circuit like. For nanotori at low temperatures, a modification of the ratio between torus minor and major radius gives either configurations with only toroidalmoment or configurations in which it coexists with homogeneous or oscillating hypertoroidal moment.

Concentrations of potentially toxic metals in surface soils are important to investigate before building new residential areas. Prior to development of a residential area in Sundsvall, northern Sweden, it was observed that barium (Ba) concentrations in the soil at the site exceeded the guideline value of 200 mg kg-1 outlined by the Swedish Environmental Protection Agency. In this study, I aimed at determining the reason for the high Ba concentrations in the O horizon of soils from this latter area. 49 O horizon samples were collected from two separate transects (about 36 km long). A total of 43 Scots pine (Pinus sylvestris) needles were collected from both transects to determine potential Ba accumulation in plants. The O horizon and pine needle samples were analyzed using X-ray fluorescence spectrometer (XRF) to determine Ba concentrations. The total mean concentration of Ba was 426±289 mg kg-1 without any relationship to industrial sources. Barium concentrations were negatively correlated to soil organic matter (r = -0.885). Correlations between Ba, aluminum (Al), silicon (Si) and potassium (K) was r = 0.565, r = 0.486 and 0.525, a finding that suggests a strong positive coupling to elements typically found in silicate minerals. Barium concentrations in pine needle samples were below limit of detection (<LOD) suggesting that “plant pumping” via roots to the soil surface was an unlikely explanation for high concentrations in the O horizon. I conclude that the minerals in the O horizon originate from inmixing from the underlying mineral soil, therefore, high Ba concentrations in the study area is likely due to naturally occurring minerals.

We have applied an electrophysiologic technique (Reuss L.(1985) Proc. Natl. Acad. Sci. USA 82, 6014) to measure changes in steady-state hepatocyte volume during osmotic stress. Hepatocytes in mouse liver slices were loaded with tetramethylammonium ion (TMA+) during transient exposure of cell to nystatin. Intracellular TMA+ activity (αiTMA) was measured with TMA+ -sensitive, double-barrelled microelectrodes. Loading hepatocytes with TMA+ did not change their membrane potential (Vm), and under steady-state conditions αiTMA remained constant over 4 min in a single impalement. Hyperosmotic solutions (50, 100 and 150 mM sucrose added to media) and hyposmotic solutions (sucrose in media reduced by 50 and 100 mM) increased and decreased αiTMA, respectively, which demonstrated transmembrane water movements. The slope of the plot of change in steady-state cell water volume, [(αiTMA)O/(αiTMA)4min] - 1, on the relative osmolality of media, (experimental mosmol/control mosmol) -1, was less than predicted for a perfect osmometer. Corresponding measurements of Vm showed that its magnitude increased with hyposmolality and decreased with hyperosmolality. When Ba2+ (2 mM) was present during hyposmotic stress of 0.66 × 286 mosmol (control), cell water volume increased by a factor of 1.44 ± 0.02 compared with that of hyposmotic stress alone, which increased cell water volume by a factor of only 1.12 ± 0.02, P< 0.001. Ba2+ also decreased the hyperpolarization of hyposmotic stress from a factor of 1.62 ± 0.04 to 1.24 ± 0.09, P < 0.01. We conclude that hepatocytes partially regulate their steady-state volume during hypo- and hyperosmotic stress. However, volume regulation during hyposmotic stress diminished along with hyperpolarization of Vm in the presence of the K+ -channel blocker, Ba2+. This shows that variation in Vm during osmotic stress provides an intercurrent, electromotive force for hepatocyte volume regulation.

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Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Includes bibliographical references. / M.S.