Investigating the orientation dependence on functional properties in Bi0.5Na0.5TiO3-BaTiO3 films

• Orientation dependence of functional properties is studied in epitaxial BNTBT films. • Epitaxial symmetry is used to tune polar nanodomain structure in BNTBT based system. • Threefold rotational symmetry enhances the relaxor ergodicity in BNTBT thin film. • The (001) orientation is more effective for enhancing the piezoelectric response. • The energy storage efficiency is improved in (111) oriented BNTBT films. The morphotropic phase boundary (MPB) composition in lead free (1-x) Bi 0.5 Na 0.5 TiO 3 – x BaTiO 3 (BNTBT) solid solution has attracted extensive research due to its significant potential for piezoelectric and high-power energy storage applications. Here, epitaxial (001) and (111) BNTBT films with composition around the MPB are investigated. A complex domain pattern is evidenced for both film orientation, due to the coexistence of a weak polar phase and a strong polar ferroelectric phase. An electric field induced phase switching is shown in both (001) and (111) oriented film, as well as a weakening of the polar state in the (111) BNTBT film. The enhanced ergodic relaxor state in the (111) BNTBT film gives rise to a reduced piezoelectric response and improved energy storage performances. The epitaxial symmetry engineering is shown to provide a complementary approach to the composition strategy to improve the functional properties in BNTBT films.