No description available.

Using a combination of dielectric spectroscopy and atomistic computer simulation techniques, the dynamical behaviour of loosely bound cations in the stuffed-silica minerals nepheline, yoshiokaite and ß-eucryptite has been investigated. The investigation has been extended to include the feldspar minerals albite, K-feldspar and anorthite. The low-frequency dielectric properties of all of the minerals have been investigated from room temperature to 1100 K. At each temperature, the dielectric constant, conductivity and dielectric loss were determined over a range of frequencies from 100 Hz to 10 MHz. At high temperatures distinct Debye-type relaxation processes were observed, from which activation energies were determined for each system studied. In order to rationalise these data, in the context of actual ionic mobility mechanisms, atomistic simulation.- techniques were used to elucidate the mechanisms and energetics of cation migration. Good correlation between experimentally determined and calculated energy barriers has been demonstrated. The results obtained from computer modelling confirm the nature of the processes responsible for the observed dielectric behaviour. Furthermore, they reveal the importance of framework relaxation effects in the facilitation of ion migration within a structure. This study demonstrates that short-range ionic mobility in framework silicates can be described using conventional (Debye-type) activated "hopping" models. A detailed interpretation of the mechanism of these processes has been possible by a combination of dielectric spectroscopy and computer modelling techniques. By applying the methods used here to a variety of mineral systems, it should be possible to develop a comprehensive body of transferable data relating structural aspects of framework minerals to the systematic prediction of ion migration mechanisms and energetics.

Th.--Sc. phys.--Nancy, 1967. / Bibliogr. pp. 91-95.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1901. / Leaves 3-7 missing from original text. The entire thesis text is included in file. Typescript. Illustrated by authors. Title from title screen of thesis/dissertation PDF file (viewed March 25, 2010)

Thesis (M.S.)--University of Wisconsin--Madison, 1973. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 73-76).

Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 46).

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 164-168).

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Th. univ.--Géol.--Rennes 1, 1995.

Cette thèse a pour objet l’élaboration et la caractérisation d’oxyapatite silicatées de lanthane, matériaux potentiellement utilisables comme électrolyte pour piles à combustible à oxyde solide. Des poudres et céramiques denses d’apatite de stœchiométries en oxygène et de compositions (substitutions) différentes ont été élaborées par réaction à l’état solide à haute température. Il ressort que quelque soit la composition, le paramètre principal qui gouverne les propriétés de conduction est la stœchiométrie en oxygène. La conductivité atteint 1,7 x 10-2 S.cm-1 à 700°C pour la composition La10Si5,5Mg0,5O26,5. La combinaison d’analyses spectroscopiques (Diffusion Raman, Résonance Magnétique Nucléaire) et de diffraction des neutrons a permis de définir un mécanisme de conduction des ions oxydes dans la structure. L’existence d’un site interstitiel localisé dans les canaux de la structure apatite en (-0,01, 0,04, 0,06) est confirmée. Un chemin de diffusion des ions oxyde de type « lacune sur le site 2a – atome interstitiel » est proposé le long de l’axe c. Ce mécanisme semble facilité par le déplacement des tétraèdres situés à la périphérie du canal. / This work is devoted to the elaboration and the characterisation of apatite type lanthanum silicates as new electrolyte for SOFC fuel cells. Apatite powders and dense ceramics with different oxygen stoichiometries and compositions (substitutions) were prepared by high temperature solid state reaction. Whatever the composition, we can conclude that the key parameter which governs the conduction properties is the oxygen stoichiometry. The conductivity reaches 1.7 x 10-2 S.cm-1 at 700°C for the La10Si5,5Mg0,5O26,5 composition. By combining Raman spectroscopy, NMR and neutron diffraction, an oxide ion conduction mechanism was deduced. The existence of an interstitial site located at (-0.01, 0.04, 0.06) was confirmed. This allows to proposed a realistic oxygen diffusion pathway through this interstitial site along the c axis. Moreover, this mechanism seems to be facilitated by the displacement of tetrahedral located at the periphery of the oxide channels.