The microstructure and interfaces of intermediate layers in sapphire bicrystals

The structure of different intermediate layers and their interfaces was studied in sapphire bicrystals by high resolution electron microscopy (HREM), selected area electron diffraction (SAED) and energy dispersive X-ray analysis (EDX). The intermediate layer of Y3Al5O12 between two sapphire bicrystal parts, was found to be polycrystalline with three major orientations between sapphire and Y3Al5O12. The structure of the Y3Al5O12/sapphire interfaces is described. Sapphire bicrystals with a multilayer of Y-stabilized ZrO2 (YSZ) and sapphire (Al2O3) as intermediate layer, are also studied. Recrystallization of the intermediate layers occurred during the solid phase intergrowth of the sapphire bicrystals parts and only an YSZ layer was found as intermediate layer. The misorientation between the consecutive YSZ grains is less than 1.5°. Misfit dislocation and atomic height steps decorate the YSZ/sapphire interface.