Abstract
A glass with the composition 2BaO·TiO2·2.75SiO2 was annealed at 810 °C for 20 h. This led to surface crystallization. Immediately at the surface of the sample, a layer of Ba2TiSi2O8-type fresnoite crystals (layer I), with a thickness of approximately 7 μm, oriented with the crystallographic [101]-direction perpendicular to the surface, was formed. The pole of the (001)-plane rotates randomly around the [101]-direction. It is assumed that nucleation kinetics is decisive to the direction of growth. In the next layer (layer II), the crystals are oriented with the crystallographic [001]-direction (c-axis) perpendicular to the surface of the sample. This layer occurs at a distance of 7−60 μm from the surface. Here, crystals that are not oriented in that way hinder each other during crystal growth. At a distance > 60 μm, the orientation of the fresnoite crystals is random and is the result of volume crystallization. The main characterization method is electron backscatter diffraction/orientation imaging microscopy.
Published Version
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