Tailoring the orientations of complex niobate films on perovskite substrates

Ferroelectric complex niobates with tetragonal tungsten bronze (TTB) structure are of significant interest for a variety of device applications. For many of these applications thin films are required whose properties, due to the particular structure, are sensitively dependent on the film structure and orientation. Based on the system of the relaxor Ca_XBa_1-XNb₂O₆ (CBN) and the perovskite substrate SrTiO₃ (STO) the crystal orientation relationships between film and substrate are determined as (0 0 1)_CBN//{0 0 1}_STO, [1 0 0]_CBN//〈1 3 0〉_STO, and [ 0 1 0 ]_CBN / / 〈 over(1, ̄) 3 0 〉_STO. Employing an advanced imaging technique in an aberration-corrected transmission electron microscope we reveal the atomic configuration of both the cation and oxygen columns at the heterointerface. The interface structure as well as the orientation relations can be understood in terms of lowest-energy considerations based on a near-coincidence site lattice model. These results reveal a pathway for tailoring the film orientation of TTB niobates on perovskites for optimizing the film properties for device applications.