Orientation dependence on piezoresponse of lead-free piezoelectric sodium bismuth titanate epitaxial thin films

Lead-free piezoelectric sodium bismuth titanate ((Bi0.5Na0.5)TiO3, BNT) thin films were epitaxially grown onto (001)-, (110)-, and (111)-oriented Nb:SrTiO3 (STO) single crystal substrates prepared by sol-gel processing. Highly oriented growth in (001), (110), and (111) BNT thin films was obtained in this work benefiting from the lattice match between the BNT film and the STO substrate. The different growth models in thin films with various orientations result in various surface morphologies dependent on the film orientation. The piezoresponse of the BNT thin films was represented exhibiting a strong orientation dependence that (110)>(001)>(111). This is contributed by the various domain switching contribution related to the crystal symmetry and polarization distribution in the three oriented thin films.