Ferroelectric domain structure evolution in Ba(Zr0.1Ti0.9)O3/(Ba0.75Ca0.25)TiO3 heterostructures

Highly oriented multilayerd Ba(Zr0.1Ti0.9)O3/(Ba0.75Ca0.25)TiO3 thin films were fabricated on Nb doped (001) SrTiO3 (Nb:STO) substrates by pulsed laser deposition. Microstructural characterization by X-ray diffraction indicates that the as-deposited multilayered thin films are highly c-axis oriented. Transmission electron microscopy shows that the films present epitaxial correspondence with the substrate at the first layer and multi-oriented twin domain structures near the surface, especially with increasing periodic number (N). Piezoresponse force microscopy (PFM) studies reveal an intense polarization component in the out-of-plane direction, which increases greatly with increasing periodic number (N), whereas the in-plane shows inferior phase contrast. The optimized combination was found to be the annealed 16 layer structure (N = 8, layer thickness = 712 nm) which displays the best polarization domain structures and the saturated piezo response loop. The annealing process benefits the 180° domains with the same angle in the growth direction, which brings more piezo response in the in-plane signal. Our results suggest that the increasing of piezo response is greatly associated with the interface effect and the twining structure.