Phase transition in ferroelectric Pb(Zr0.52Ti0.48)O3 epitaxial thin films

• We report on the thickness dependency of phase transition in epitaxial Pb(Zr0.52Ti0.48)O3 films.
• The films were analyzed by X-ray diffraction and spectroscopic ellipsometry.
• This phase transition was found to be related to a Zr/Ti composition gradient.

PbZr1 −xTixO3 (PZT) has been intensively studied for various ferroelectric applications. Its promising application for micro-electro-mechanical system has reignited the interests due to its outstanding ferroelectric and piezoelectric properties. Most PZT ceramics employed in devices are synthesized with a Zr/Ti ratio close to the tetragonal–rhombohedral morphotropic phase boundary (x = 0.48) due to its high electro-mechanical coupling at this composition. Morphotropic phase boundary is particularly interesting to study for the investigation of phase transition. In this work, we report the epitaxial growth and electrical characterization of epitaxial PZT (Zr/Ti = 52/48) thin films on Nb-doped SrTiO3. PZT films, with thickness from 30 nm to 65 nm, were deposited by sol–gel method and eventually crystallized at 700 °C by rapid thermal annealing in oxygen. Film ferroelectricity was confirmed by Sawyer–Tower circuit measurement. X-ray diffraction analysis indicates a thickness-dependent structural phase, i.e., a phase transition from tetragonal phase for the thinner film to a biphasic (tetragonal + pseudo-cubic) structure for the thicker film, which is characterized by ellipsometry as a phase separation from the bottom surface of the film to the top one. This phase transition is related to a composition gradient within the film thickness.