New Insights into the Microstructure of Oriented Fresnoite Dendrites in the System Ba₂TiSi₂O₈−SiO₂ Through Electron Backscatter Diffraction (EBSD)

Abstract

A glass with the composition Ba 2 TiSi 2.75 O 9.5 was crystallized by electrochemically induced nucleation. A dc-voltage (4.8 V) was attached between a platinum crucible containing the melt and a platinum wire inserted into the melt. The platinum wire was the cathode. After 2 min, crystals were formed at the cathode, which grew toward the crucible. These crystals consisted of fresnoite Ba 2 TiSi 2 O 8 , were highly oriented, and showed dendritic growth. These structures were characterized in detail by using electron backscatter diffraction/orientation imaging microscopy. Only a few crystals deviate from the main orientation of the respective dendrite. They were located and quantified. Intermediate areas between dendrites were analyzed, and the true boundaries of areas with homogeneous orientation are presented. The orientation is not as pronounced in the first 600 μm next to the platinum wire.

Viscous Fingering and Dendritic Growth of Surface Crystallized Sr2TiSi2O8 Fresnoite

“…The black area in the map was caused by a lowered EBSD-pattern quality due to a previously performed EBSD-scan of higher detail attempting to resolve the individual dendritic structures. At a first glace it appears as though the crystal orientations within the dendrites of the IPF + IQ-map are homogeneous as expected and dendritic fragmentation1638 is not observed. However, the more detailed orientation analysis presented in the orientation + IQ-map (inset) shows a systematic orientation change of up to 20° near the tips of the dendrites.…”

“…Subsequently a slow, continuous growth selection changes the texture towards the [001]-direction being tilted by about 45° from the surface normal after 300 μm of growth into the bulk. The additional SiO 2 in the glass melt is added to allow comparability to the surface crystallization experiments of barium titanium silicate (BTS1) and STS5 and experiments concerning the electrochemically induced nucleation of fresnoite in glasses1516171819. It was initially chosen to ease glass preparation and controlled crystallization as the nucleation tendency of the glass is reduced by the added SiO 2 .…”

Oriented Nucleation of both Ge-Fresnoite and Benitoite/BaGe4O9 during the Surface Crystallisation of Glass Studied by Electron Backscatter Diffraction

“…Highly oriented glass-ceramics containing e.g. BTS and STS have also been produced using the method of electrochemically induced nucleation (EiN)2526272829. Furthermore, BTG has been crystallized in glasses by laser irradiation3031 or drawn into fibers and subsequently crystallized22.…”

Microstructure of Transparent Strontium Fresnoite Glass-Ceramics

“…Fresnoite of the composition Ba 2 TiSi 2 O 8 (BTS) may form solid solutions with the systems Sr 2 TiSi 2 O 8 (STS, recently studied by synchrotron X-ray powder diffraction56) and Ba 2 TiGe 2 O 8 where GeO 2 is used to substitute SiO 2 78910. While oriented fresnoite has been prepared in the form of thin films1112 or thin crystal lines written in a glass matrix by laser induced crystallization1314, larger bodies of oriented fresnoite glass-ceramics may be produced by electrochemically induced nucleation15 and surface crystallization. While temperature gradients have been applied during the latter in the past1617, more recent results have shown that oriented layers of crystals also occur without this experimental effort.…”