Regensburg 2007 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 11: Interfaces III

MM 11.2: Vortrag

Montag, 26. März 2007, 15:00–15:15, H6

The role of crystallography in topotaxial first-phase selection — •Andriy Lotnyk, Stephan Senz, and Dietrich Hesse — Max Planck Institute of Microstructure Physics

The role of crystallography in topotaxial first phase formation in the MgO-TiO₂ system is studied. The question which phase forms first in a thin-film solid state reaction, if the corresponding phase diagram permits the formation of several phases, is of considerable scientific and technological significance. Correspondingly, a number of models have been put forward, including kinetic, thermodynamic, and nucleation-related models. In the present work, vapor-solid reactions between MgO (vapor) and TiO₂ (rutile) single crystals with different surface orientations were performed. The crystallographic relations between the product phases and the TiO₂ substrates were studied by X-ray diffractometry and transmission electron microscopy. A topotaxial formation of MgTiO₃ on the rutile crystals was found. Previous results on vapor-solid reactions of TiO₂ (vapor) with MgO substrates showed the topotaxial formation of Mg₂TiO₄. We conclude that in the MgO-TiO₂ system, in case of a topotaxial solid state reaction, the phase forming first depends on the crystallography of the substrate serving as reactant. Thus, crystallography obviously can play an important role in the determination of the first growing phase in topotaxial solid-state reactions.