Pseudo‐Ferroelectric Domain‐Wall in Perovskite Ferroelectric Thin Films

Abstract

Perovskite ferroelectric thin films exhibit unique dielectric and piezoelectric properties owing to their internal polarized domains that accommodate the out‐of‐plane (ferroelectric) and in‐plane (ferroelastic) polarization‐induced electrostatic and elastic energy. These domains are generally treated as 2D defects with distinctive differences in domain morphology and domain‐wall characteristics, although they are indeed 3D volumetric defects. Here, by using atomistic simulation and microscopy characterization, a “pseudo‐ferroelectric domain” that has the morphology similar to a ferroelectric domain but holds the same defect character of ferroelastic domain‐wall, i.e., semi‐coherent (100)matrix||(100)domain interface is identified. Such pseudo‐ferroelectric domain walls will play a critical role in the migration kinetics of ferroelastic domains and in the piezoelectric responses of ferroelectric thin films during cyclic mechanical/electrical loading. The study throws light on a novel aspect of domains, namely, the 3D configuration and mobility of domain walls, and their role in the overall domain engineering.

Atomistic Insights into Nucleation of Ferroelastic Domains in PbTiO3

“…7−10 Domains in perovskite ferroelectric materials are categorized as ferroelectric (FC) and ferroelastic (FS) domains with different rotation of polarization directions (P d ) with respect to matrix (P m ). 11 Nucleation of FC domains does not alter the crystal lattice (see Supplementary Note 1 and Figure S1a), which simply reacts to electric fields. 12−17 In contrast, nucleation of FS domains changes the crystal orientation (see Supplementary Note 1 and Figure S1b) and manifests distinction in polarization directions, which reacts to both electric 18−20 and elastic fields.…”

“…Domains in perovskite ferroelectric materials are categorized as ferroelectric (FC) and ferroelastic (FS) domains with different rotation of polarization directions (P d ) with respect to matrix (P m ) . Nucleation of FC domains does not alter the crystal lattice (see Supplementary Note 1 and Figure S1a), which simply reacts to electric fields. − In contrast, nucleation of FS domains changes the crystal orientation (see Supplementary Note 1 and Figure S1b) and manifests distinction in polarization directions, which reacts to both electric − and elastic fields. , However, the nucleation process of FS domains cannot be captured experimentally because of the technical challenges , in manipulating and isolating the ultrafast (might be supersonic) thermodynamic process. , Nucleation sites of FS domains were thus speculated based on characterization of microscale domain patterns. − The domain switching is treated as a one-step process.…”

“…A FS domain can be crystallographically treated as a deformation twin with the twinning plane (110). , The (110) m ∥(110) d and (001) m ∥(001) d DWs are identified as primary twin boundaries (TBs) on normal and lateral sides of a (110) twin (for simplicity, the crystallographic directions and planes in the matrix and twin (domain) will be identified by subscripts m and d ). Nucleation of FS domains should share similarities with the nucleation mechanism of deformation twins.…”

“…The formation of misfit dislocations on (001) m ∥(001) d DWs has been confirmed by both atomistic simulation and microscopy characterization. 11,66 The formation process of misfit dislocations is schematically depicted in Figure 4a 1 −a 3 . According to the Frank−Bilby theory, 67 with coherency stress relaxation, the angle between (100) m and (100) d planes gradually decreases from 90.0°to 87.6°(Supplementary Note 8 and Figure S9).…”