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Atomic-scale mapping of dipole frustration at 90° charged domain walls in ferroelectric PbTiO3 films.

Tang YL, Zhu YL, Wang YJ, Wang WY, Xu YB, Ren WJ, Zhang ZD, Ma XL - Sci Rep (2014)

Bottom Line: Besides the well-accepted head-to-tail 90° uncharged domain-walls, we have identified not only head-to-head positively charged but also tail-to-tail negatively charged domain-walls.The widths, polarization distributions, and strains across these charged domain-walls are mapped quantitatively at atomic scale, where remarkable difference between these domain-walls is presented.This study is expected to provide fundamental information for understanding numerous novel domain-wall phenomena in ferroelectrics.

View Article: PubMed Central - PubMed

Affiliation: 1] Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, 110016 Shenyang, China [2].

ABSTRACT
The atomic-scale structural and electric parameters of the 90° domain-walls in tetragonal ferroelectrics are of technological importance for exploring the ferroelectric switching behaviors and various domain-wall-related novel functions. We have grown epitaxial PbTiO3/SrTiO3 multilayer films in which the electric dipoles at 90° domain-walls of ferroelectric PbTiO3 are characterized by means of aberration-corrected scanning transmission electron microscopy. Besides the well-accepted head-to-tail 90° uncharged domain-walls, we have identified not only head-to-head positively charged but also tail-to-tail negatively charged domain-walls. The widths, polarization distributions, and strains across these charged domain-walls are mapped quantitatively at atomic scale, where remarkable difference between these domain-walls is presented. This study is expected to provide fundamental information for understanding numerous novel domain-wall phenomena in ferroelectrics.

No MeSH data available.


2-D mappings of structural and electric behaviors showing the differences between 90° CDWs and 90° UCDWs.(a, b) Out-of-plane lattice spacing mapping for the 90° PCDW and NCDW. (c, d) Lattice gradient mappings (lattice gradient of the out-of-plane lattice mappings along in-plane direction, mapped unit-cell by unit-cell) for the two types of domains. Note the alleviated lattice gradient across the 90° CDWs, especially of the 90° PCDW, compared with sharp lattice gradient across the 90° UCDWs. (e, f) Ps angle mappings for the two types of domains. The definition of 0°, 90°, 180°, and 270° are marked with colored arrows with corresponding color-scale. In case of the 90° PCDW, the Ps angles are markedly disordered.
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f7: 2-D mappings of structural and electric behaviors showing the differences between 90° CDWs and 90° UCDWs.(a, b) Out-of-plane lattice spacing mapping for the 90° PCDW and NCDW. (c, d) Lattice gradient mappings (lattice gradient of the out-of-plane lattice mappings along in-plane direction, mapped unit-cell by unit-cell) for the two types of domains. Note the alleviated lattice gradient across the 90° CDWs, especially of the 90° PCDW, compared with sharp lattice gradient across the 90° UCDWs. (e, f) Ps angle mappings for the two types of domains. The definition of 0°, 90°, 180°, and 270° are marked with colored arrows with corresponding color-scale. In case of the 90° PCDW, the Ps angles are markedly disordered.

Mentions: To directly visualize the 2D structural parameters and Ps angles, unit-cell-wise structure and Ps angle mapping are displayed. The lattice parameter, gradient of the lattice parameter and Ps angles of the PTO unit-cells near the 90° PCDW and NCDW are mapped unit-cell by unit-cell, as shown in Figure 7. The out-of-plane lattice spacing mapping results clearly exhibit the 90° UCDWs, since there is sudden jump of the lattice spacing (blue to green, presumably corresponds to 0.39–0.42 nm, Fig. 7a, b). Although the 90° PCDW is diffused since the lattice spacing slowly changes from 0.395 to 0.42 nm (light blue to white then to green) with a width about several tens unit-cells (Fig. 7a, which is consistent with Fig. 2e), we note that the 90° NCDW is much sharper (Fig. 7b). To visually show the differences among the uncharged, positively and negatively-charged 90° DWs, in-plane lattice gradient of the out-of-plane lattice spacing are mapped. The lattice gradient is defined as /cx+1 − cx//1U.C., where cx denotes an out-of-plane lattice spacing and cx+1 denotes the out-of-plane lattice spacing of the right neighbor unit-cell of cx, and ‘unit-cell' is abbreviated as ‘U.C.', (Fig. 7c, d). The uniform dark blue means there is no in-plane lattice gradient since there is no lattice change in a single domain. The sudden change of lattice c to a (or a to c) across the 90° UCDWs makes obvious contrast in figure 7c, d. The maximum of the lattice gradient is about 0.01 to 0.015 nm/U.C. across the 90° UCDWs. It is clear that the left 90° UCDW in figure 7c terminates in the matrix, which results in the formation of the 90° PCDW. Compared with the uncharged DWs, the lattice gradient of the 90° PCDW is invisible (Fig. 7c), this means the lattice change across the 90° PCDW is much slower. Such a status is also seen in figure 2e. However, the 90° NCDW possesses visible lattice gradient (Fig. 7d). Moreover, the lattice gradient of the upper segment is comparable to the 90° UCDW (note that their color-scales are almost the same). Nevertheless, as seen in figure 7d, the color-scale of the 90° NCDW changes gradually from green to light blue as the DW tracing from top to bottom. This indicates that when the 90° NCDW reaches the PTO/STO interface, the lattice gradient is continuously relieved. In addition, the DW is broadened simultaneously with relief of the lattice gradient, as marked with the violet dotted lines (Fig. 7d). Such a status is also seen in figure 5m.


Atomic-scale mapping of dipole frustration at 90° charged domain walls in ferroelectric PbTiO3 films.

Tang YL, Zhu YL, Wang YJ, Wang WY, Xu YB, Ren WJ, Zhang ZD, Ma XL - Sci Rep (2014)

2-D mappings of structural and electric behaviors showing the differences between 90° CDWs and 90° UCDWs.(a, b) Out-of-plane lattice spacing mapping for the 90° PCDW and NCDW. (c, d) Lattice gradient mappings (lattice gradient of the out-of-plane lattice mappings along in-plane direction, mapped unit-cell by unit-cell) for the two types of domains. Note the alleviated lattice gradient across the 90° CDWs, especially of the 90° PCDW, compared with sharp lattice gradient across the 90° UCDWs. (e, f) Ps angle mappings for the two types of domains. The definition of 0°, 90°, 180°, and 270° are marked with colored arrows with corresponding color-scale. In case of the 90° PCDW, the Ps angles are markedly disordered.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3927212&req=5

f7: 2-D mappings of structural and electric behaviors showing the differences between 90° CDWs and 90° UCDWs.(a, b) Out-of-plane lattice spacing mapping for the 90° PCDW and NCDW. (c, d) Lattice gradient mappings (lattice gradient of the out-of-plane lattice mappings along in-plane direction, mapped unit-cell by unit-cell) for the two types of domains. Note the alleviated lattice gradient across the 90° CDWs, especially of the 90° PCDW, compared with sharp lattice gradient across the 90° UCDWs. (e, f) Ps angle mappings for the two types of domains. The definition of 0°, 90°, 180°, and 270° are marked with colored arrows with corresponding color-scale. In case of the 90° PCDW, the Ps angles are markedly disordered.
Mentions: To directly visualize the 2D structural parameters and Ps angles, unit-cell-wise structure and Ps angle mapping are displayed. The lattice parameter, gradient of the lattice parameter and Ps angles of the PTO unit-cells near the 90° PCDW and NCDW are mapped unit-cell by unit-cell, as shown in Figure 7. The out-of-plane lattice spacing mapping results clearly exhibit the 90° UCDWs, since there is sudden jump of the lattice spacing (blue to green, presumably corresponds to 0.39–0.42 nm, Fig. 7a, b). Although the 90° PCDW is diffused since the lattice spacing slowly changes from 0.395 to 0.42 nm (light blue to white then to green) with a width about several tens unit-cells (Fig. 7a, which is consistent with Fig. 2e), we note that the 90° NCDW is much sharper (Fig. 7b). To visually show the differences among the uncharged, positively and negatively-charged 90° DWs, in-plane lattice gradient of the out-of-plane lattice spacing are mapped. The lattice gradient is defined as /cx+1 − cx//1U.C., where cx denotes an out-of-plane lattice spacing and cx+1 denotes the out-of-plane lattice spacing of the right neighbor unit-cell of cx, and ‘unit-cell' is abbreviated as ‘U.C.', (Fig. 7c, d). The uniform dark blue means there is no in-plane lattice gradient since there is no lattice change in a single domain. The sudden change of lattice c to a (or a to c) across the 90° UCDWs makes obvious contrast in figure 7c, d. The maximum of the lattice gradient is about 0.01 to 0.015 nm/U.C. across the 90° UCDWs. It is clear that the left 90° UCDW in figure 7c terminates in the matrix, which results in the formation of the 90° PCDW. Compared with the uncharged DWs, the lattice gradient of the 90° PCDW is invisible (Fig. 7c), this means the lattice change across the 90° PCDW is much slower. Such a status is also seen in figure 2e. However, the 90° NCDW possesses visible lattice gradient (Fig. 7d). Moreover, the lattice gradient of the upper segment is comparable to the 90° UCDW (note that their color-scales are almost the same). Nevertheless, as seen in figure 7d, the color-scale of the 90° NCDW changes gradually from green to light blue as the DW tracing from top to bottom. This indicates that when the 90° NCDW reaches the PTO/STO interface, the lattice gradient is continuously relieved. In addition, the DW is broadened simultaneously with relief of the lattice gradient, as marked with the violet dotted lines (Fig. 7d). Such a status is also seen in figure 5m.

Bottom Line: Besides the well-accepted head-to-tail 90° uncharged domain-walls, we have identified not only head-to-head positively charged but also tail-to-tail negatively charged domain-walls.The widths, polarization distributions, and strains across these charged domain-walls are mapped quantitatively at atomic scale, where remarkable difference between these domain-walls is presented.This study is expected to provide fundamental information for understanding numerous novel domain-wall phenomena in ferroelectrics.

View Article: PubMed Central - PubMed

Affiliation: 1] Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, 110016 Shenyang, China [2].

ABSTRACT
The atomic-scale structural and electric parameters of the 90° domain-walls in tetragonal ferroelectrics are of technological importance for exploring the ferroelectric switching behaviors and various domain-wall-related novel functions. We have grown epitaxial PbTiO3/SrTiO3 multilayer films in which the electric dipoles at 90° domain-walls of ferroelectric PbTiO3 are characterized by means of aberration-corrected scanning transmission electron microscopy. Besides the well-accepted head-to-tail 90° uncharged domain-walls, we have identified not only head-to-head positively charged but also tail-to-tail negatively charged domain-walls. The widths, polarization distributions, and strains across these charged domain-walls are mapped quantitatively at atomic scale, where remarkable difference between these domain-walls is presented. This study is expected to provide fundamental information for understanding numerous novel domain-wall phenomena in ferroelectrics.

No MeSH data available.