Epitaxial growth map for Bi₄Ti₃O₁₂ films: A determining factor for crystal orientation

Bi₄Ti₃O₁₂ films were epitaxially grown at 600-750°C on various types of single-crystal oxide substrate by metal-organic chemical vapor deposition. In terms of the oxygen interatomic distances of the substrates used, the crystal orientations of the deposited epitaxial films were classified into three groups: (118), in-plane c-axis, and (001) orientations. The films on substrates with an oblong in-plane oxygen unit, had a (100)/(010) and/or (118) orientation, wheras those on substrates with a square in-plane oxygen unit had (001) or (hk0)/(kh0) orientation. There was an intermediate region between the (100)/(010) and (118) orientations at the present deposition temperature, where both orientations coexisted. As a result, the relationship between in-plane oxygen interatomic distances of the substrates and film orientation was summarized into an epitaxial growth map. This map is applicable to the epitaxial growth of other bismuth-layer-structured ferroelectric thin films.