Epitaxial growth and piezoelectric characterization of the (1―x)BiScO3―(x)PbTiO3 ultrathin film

We studied ferroelectric properties of morphotropic phase boundary (1−x)BiScO3−(x)PbTiO3 (BSPT, x = 0.64) epitaxial thin films on SrTiO3 (001) and Nb:SrTiO3 (001). BSPT thin films with various thicknesses were deposited using off-axis radio frequency magnetron sputtering. By analyzing x-ray data of BSPT thin films with various thicknesses, we confirmed that films thinner than ∼22 nm were in a strained state. Films thicker than ∼22 nm were in a relaxed state because of the strain relaxation mechanism caused by misfit dislocation formation. Clear piezoresponses and polarization reversal phenomena can be observed in the ultrathin limit down to 8 nm through Piezo Force Microscope experiments. The piezoresponse data as a function of thickness correlates with the structural modification of thin films.