Atomic-scale insight into the epitaxial growth mechanism and interfacial coupling of BNT film prepared by hydrothermal synthesis

Revealing the epitaxial growth mechanism and the interfacial coupling effect between oxide films will help to build a “structure-property” bridge for the design of microelectronic devices. Here, the epitaxial growth mechanism and the interfacial coupling in Bi_0.5Na_0.5TiO₃/SrTiO₃ (BNT/STO) heterointerfaces are investigated by the aberration-corrected scanning transmission electron microscopy, which is synthesized by a hydrothermal method. The results illustrate that 4 mol/L NaOH leads to not only the epitaxial growth of the BNT film but also the mutual diffusion of elements. The uneven distribution of local elements in BNT films is observed and confirmed to impact the cation displacements of B-site and lattice distortion. However, the overall trend of B-site cation displacement at the BNT/STO heterointerfaces is dominated by the interfacial strain. Additionally, the oxygen octahedral tilt exhibits continuous tilt patterns of a⁰a⁰a⁰ - a⁻b⁰c⁻ - a⁰a⁰c⁻ - a⁰b⁻c⁻ - a⁻b⁻c⁻ from the substrate to BNT film due to the constraint of the substrate and presents a strong correlation with cation displacement. These results are helpful to understand the underlying atomic structures and physical properties of BNT epitaxial thin films.