Exploring the polarization reorientation in polycrystalline ferroelectric thin films from the macroscopic and nanoscopic perspectives

Abstract

In this work, combining macroscopic and nanoscopic analyses, we explored the role of domain structure and relative domain-electric field orientations in the polarization reorientation process in polycrystalline ferroelectric thin films. Results of macroscopic ferroelectric and dielectric measurements were interpreted considering a detailed characterization of the domain structure, performed by piezoresponse force microscopy (PFM). A phenomenological model was utilized to obtain macroscopic parameters related to the polarization reorientation, domain structure, and domain wall mobility. We investigated tetragonal Pb(Zr, Ti)O3 (PZT) thin films with preferential in-plane polarization ([100] direction) and mixed in-plane and out of plane polarization ([100] and 〈110〉 directions). Results revealed similar domain structures for the films, consisting of a high density of stripe domains, with a width of 10 – 15 nm, separated by 90∘ walls. With the application of an electric field, such a structure is rearranged but maintained a high density of 90∘ walls after removing the field. Combining the macroscopic and nanoscopic analyses, we found that the relative polarization orientation of the domains significantly impacts the reorientation process. For the [100] oriented film, the reorientation occurs mainly by the rotation of a-domains. For these films, the c-domain configuration is very unstable, resulting in a high backswitching of the polarization after removing the field. On the other side, the increase of the 〈110〉 film orientation represents an increase of domains with the out-of-plane component of polarization that can reorient by 180∘ or 90∘ switching and stabilize. This results in a more abrupt reorientation process and a reduction of the backswitching effect. The parameters obtained with the phenomenological model are in good agreement with the response observed by PFM and better explain the macroscopic measurements.