Crystallization of calcium hexaluminate on basal alumina

Abstract

The epitactic growth of calcium hexaluminate (CA 6 ) on the basal plane of alumina was observed during an investigation of the interaction between silicate glass ® lms deposited on single-crystal alumina (a -Al 2 O 3 ). Two distinctly di erent orientation relationships occurred. The ® rst can be described as perfect hexagonon-hexagon epitaxy with (1120) CA6 i ( 1010) Al2O3 and (0001) Al2O3 i ( 0001) CA6 . This relationship has 1.1% lattice mis® t in the substrate plane; the mis® t is accommodated at the interface by a hexagonal network of mis® t dislocations. In the second relationship the CA 6 grains are rotated about the substrate normal and can be explained by the coincident-site lattice model for phase boundaries. Both orientation relationships emphasize the in¯uence of substrate crystallography on the crystallization process. §