Genesis of the (111) Twin in Barium Titanate

On the basis of the topotaxy between BaTiO 3 and Ba 6 Ti 17 O 40 found recently, a model of a nonconservative (111) twin in TiO 2 ‐rich BaTiO 3 was constructed. The model consists of several (001) layers of Ba 6 Ti 17 O 40 intergrown between (111) layers of BaTiO 3 , the core of the twin being a slightly modified double layer of Ba 6 Ti 17 O 40 containing face‐sharing octahedra. Using this model, anomalous grain growth below the eutectic temperature and preferential growth of (111) twins in a reducing atmosphere were explained, as well a nucleation of butterfly twins.