Domain wall architecture in tetragonal ferroelectric thin films

TL;DR

This study investigates the complex domain wall structures in tetragonal ferroelectric thin films, using advanced microscopy and optical techniques to understand and control their properties for improved technological performance.

Contribution

It combines STEM and SHG methods to analyze and manipulate domain wall structures in PZT films, revealing the nature of voltage-induced 180° domain walls and their polarization behavior.

Findings

Voltage can induce tilted 180° domain walls.

Domain walls exhibit mixed Ising-Néel polarization rotation.

Distribution of a-domains affects domain wall properties.

Abstract

Domain walls in ferroelectrics exhibit a plethora of phases and functionalities not found in the bulk. The interplay of electrostatic, chemical, topological, and distortive inhomogeneities at the walls can be so complex, however, that this obstructs their technological performance. In tetragonal ferroelectrics like PbZrxTi1-xO3, for example, the desired functional 180{\deg} domain walls within out-of-plane-polarized c-domains are interspersed by in-plane-polarized a-domains and the associated network of domain walls remains challenging to analyze. Here we use a combination of STEM and optical second harmonic generation (SHG) to determine the relation between strain, film thickness, local electric fields and the resulting domain and domain-wall structures across the entire thickness of a set of PZT films. We quantify the distribution of a-domains in the c-domain matrix of the films. Using locally applied electric fields we control the a/c distribution and induce the technologically preferable 180{\deg} domain walls. We find that these voltage induced walls are tilted and exhibit a mixed Ising-N\'eel type transverse rotation of polarization across the wall with a specific nonlinear optical response.