Constructing Polymorphic Nanodomains in BaTiO<sub>3</sub> Films via Epitaxial Symmetry Engineering
Wei Peng, Jacob A. Zorn, Junsik Mun, Muhammad Sheeraz, Chang Jae Roh, Jun Pan, Bo Wang, Kun Guo, Chang Won Ahn, Yaping Zhang, Kui Yao, Jong Seok Lee, Jin‐Seok Chung, Tae Heon Kim, Long‐Qing Chen, Miyoung Kim, Lingfei Wang, Tae Won Noh
Abstract
Abstract Ferroelectric materials owning a polymorphic nanodomain structure usually exhibit colossal susceptibilities to external mechanical, electrical, and thermal stimuli, thus holding huge potential for relevant applications. Despite the success of traditional strategies by means of complex composition design, alternative simple methods such as strain engineering have been intensively sought to achieve a polymorphic nanodomain state in lead‐free, simple‐composition ferroelectric oxides in recent years. Here, a nanodomain configuration with morphed structural phases is realized in an epitaxial BaTiO 3 film grown on a (111)‐oriented SrTiO 3 substrate. Using a combination of experimental and theoretical approaches, it is revealed that a threefold rotational symmetry element enforced by the epitaxial constraint along the [111] direction of BaTiO 3 introduces considerable instability among intrinsic tetragonal, orthorhombic, and rhombohedral phases. Such phase degeneracy induces ultrafine ferroelectric nanodomains (1–10 nm) with low‐angle domain walls, which exhibit significantly enhanced dielectric and piezoelectric responses compared to the (001)‐oriented BaTiO 3 film with uniaxial ferroelectricity. Therefore, the finding highlights the important role of epitaxial symmetry in domain engineering of oxide ferroelectrics and facilitates the development of dielectric capacitors and piezoelectric devices.