The atomic-scale mechanism of domain wall motion in ferroelectrics is commonly accepted to be nucleation and the movement of steps on the domain walls. Although very important in understanding the mechanism of domain wall motion and domain switching, the detailed atomic structures of steps have nevertheless been scarcely explored. In this work, the charged steps of these structures on 180° domain walls in PbTiO3 were investigated using first-principles computations. Contrary to the previous understanding that there is a sudden jump at a step from one atomic plane to an adjacent plane, our computation results suggest that it is actually a gradual transition and the actual steps lie at atomic planes with the approximate Miller indices (3 0 1¯). A large polarization rotation was found around the steps, making the polarization distribution Ising–Néel-like. The barriers for the motion of steps along domain walls were found to be much lower than those for which the domain wall is moving as a whole. These findings provide valuable information for further investigations of the domain switching mechanism at the atomic scale.
Journal Article The Interactions of Ferroelectric Domain Walls and Crystallographic Defects in the PbTiO3 Films Get access Y Liu, Y Liu Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, 110016 Shenyang, China Search for other works by this author on: Oxford Academic Google Scholar Y L Tang, Y L Tang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, 110016 Shenyang, China Search for other works by this author on: Oxford Academic Google Scholar Y L Zhu, Y L Zhu Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, 110016 Shenyang, China Search for other works by this author on: Oxford Academic Google Scholar W Y Wang, W Y Wang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, 110016 Shenyang, China Search for other works by this author on: Oxford Academic Google Scholar X L Ma X L Ma Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, 110016 Shenyang, ChinaSchool of Materials Science and Engineering, Lanzhou University of Technology, Langongping Road 287, 730050 Lanzhou, China Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 1664–1665, https://doi.org/10.1017/S1431927617008984 Published: 04 August 2017
The strain coupling of misfit dislocations and ferroelastic domains is revealed in [101]-oriented PbTiO 3 /(La, Sr)(Al, Ta)O 3 films and flexoelectric-induced polarization rotation is observed around the misfit dislocation cores.
Abstract A thin film of La0 8Sr0.2MnO3, prepared by computer-controlled laser molecular-beam epitaxy, on a single-crystal SrTiO3 substrate, has been characterized by transmission electron microscopy. Electron microdiffraction and high-resolution imaging reveal that the as-received thin film with a thickness of 200 nm is epitaxially grown on the SrTiO3(001) substrate. The microstructures in the whole film are clarified in terms of the oriented microdomains. The crystallographic relationships of these domains are discussed on the basis of an orthorhombic unit cell. Theoretical calculations based on a geometrical model that was recently proposed and applied to a number of epitaxial systems have been carried out to rationalize the present observations.
Domain walls (DWs) are ubiquitous in ferroelectric materials. Ferroelastic DWs refer to those who separate two domains with unparalleled polarizations (or two different ferroelastic variants). It is long believed that the structures of ferroelastic DWs can be simply explained from the perspective of mechanical and electric compatibilities in the framework of the Landau-Ginzburg-Devonshire (LGD) theory. Here we show that the converse flexoelectricity must be taken into account for fully describing the nature of ferroelastic DWs. In our work, an unexpected asymmetric structure is identified, which is beyond the prediction of the conventional LGD theory. By incorporating the converse flexoelectricity into the LGD theory and using it to analyze high-resolution images acquired by the aberration-corrected transmission electron microscope (TEM), we demonstrate that it is the converse flexoelectricity that result in the asymmetric structure. Moreover, the flexoelectric coefficient is derived by quantifying the converse flexoelectricity around the DWs. This quantification is deterministic in both the magnitude and sign of flexoelectric coefficients, by the mutual verification of atomic mapping and first-principles calculations. Our results suggest that the converse flexoelectricity cannot be neglected for understanding the ferroelastic DWs and other boundaries in ferroelectric materials.
High-index ferroelectric films as (101)-orientated ones exhibit enhanced dielectric responses, piezoelectric responses, and exotic ferroelectric switching behaviors, which are potential candidates for applications in memories and capacitors. However, possible domain patterns and domain wall structures in (101)-oriented ferroelectric thin films are still elusive, which results in difficulties in understanding the origin and further modulating their special properties. In this work, a series of PbTiO3 (PTO) thin films with 35, 50, 60, and 70 nm in thickness were grown on (101)-oriented (LaAlO3)0.29(SrTa1/2Al1/2O3)0.71 (LSAT(101)) substrates by pulsed laser deposition and investigated by both piezoresponse force microscopy (PFM) and (scanning) transmission electron microscopy ((S)TEM). PFM measurements reveal that periodic stripe domains are dominant in 50 nm thick PTO films. Besides stripe domains, a/ c domains appear in films with thickness more than 60 nm. A thickness-dependent evolution of piezoresponse amplitude indicates that the 50 nm thick PTO films demonstrate a superior piezoresponse. Electron diffraction and contrast analysis clarify that all these (101)-oriented PTO films contain periodic stripe ferroelectric 90° domains. The domain periods increase with the film thickness following Kittel's law. Aberration-corrected STEM imaging reveals that the stripe ferroelectric 90° domains have an alternate arrangement of wide and narrow c domains with polarization directions along [100] for c1 domains and [001̅] for c2 domains, forming a "head-to-tail" polarization configuration. Further strain analysis reveals that stripe domains have uniform strain distributions and distinct lattice rotations around domain walls. It is proposed that the periodic arrangement of high-density stripe 90° domains in 50 nm thick PTO films is the main contributor to the superior piezoresponse behavior. These results are expected to provide useful information to understand the domain structures in (101)-oriented PTO thin films and thus facilitate further modulation of the properties for potential applications.
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