Polarization rotation and piezoelectricity of electric field-induced monoclinic and triclinic structures in strained PbTiO_3

摘要

Electric field-induced polarization rotation, phase changes, and piezoelectric effect of strained PbTiO_3 films have been investigated using a phenomenological approach. Low-symmetry monoclinic and triclinic structures have been induced, and the type of intermediate phases during polarization rotation is closely related to both the initial state at zero electric field and anisotropy of the in-plane strain. The monoclinic M_C and triclinic structures in general may exhibit high shear piezoelectric coefficient d_(35) and sometimes also remarkable enhancement of longitudinal piezoelectric coefficient d_(33) around the transition point. High piezoelectric activity and low critical field have been found in epitaxial PbTiO_3 with equal but opposite in-plane strain where monoclinic M_C is the only intermediate phase on the polarization path. The present results suggest that anisotropy of epitaxial strain may have significant impact on polarization rotation behavior and electromechanical coupling of ferroelectric thin films.