Origin of (111) Twin Lamellae in BaTiO₃ Thin Films on Platinum Substrates

The formation mechanisms of (111) twin lamellae in BaTiO₃ thin films were examined using transmission electron microscopy. The voids in thin films were connected with (111) twin lamellae. These voids were formed due to the incomplete coalescence of islands, and it was found that (111) twin lamellae were produced in order to accommodate the small misfit between the growing islands during contact. With respect to planar defects, the cause of the formation of (111) twin lamellae could be explained by the maintenance of a TiO₆ octahedron and the relationship with a hexagonal BaTiO₃ structure. It could be understood that the very narrow width of the twin lamellae is due to the contact process of two growing islands as well as the very small grain size of thin films.