Electron backscatter diffraction of BaAl₂B₂O₇ crystals grown from the surface of a BaO·Al₂O₃·B₂O₃ glass

A glass with the composition BaO·Al₂O₂·B₂O₃ was annealed at 780 °C for 8 h. The samples were investigated by electron backscatter diffraction (EBSD). At the surface of the samples a first layer composed of BaAl₂B₂O₇ crystals oriented with their crystallographic c-axes perpendicular to the surface was formed. This layer was highly oriented and up to 20 µm thick. In a subsequent layer, the crystals were oriented with their crystallographic c-axes parallel to the surface. While the first layer was caused by oriented nucleation at the surface, the orientation of the secondary layer was caused by kinetic selection of spherulitically grown crystals.