First-principles study of charged steps on 180° domain walls in ferroelectric PbTiO3

Y L Zhu,D Chen,X L Ma,Y X Jiang,Y J Wang

doi:10.1063/1.4997461

Abstract

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.

Highlights

It is known that the switching mechanism of the ferroelectric polarization, which essentially determines the performance of ferroelectric devices, is based on the movement of ferroelectric domain walls (DWs)
From the distributions of Pxij and Pzij for j 1⁄4 2 in the X Â 1 Â 4 supercells with the PbO (0 0 1) step model [Fig. 2(a)], we find that the magnitude of Pzij converges to 83 lC/cm2, the value in the bulk, as the distance from the DWs increases to about 2 unit cells
Using first-principles calculations, we systematically studied the structures and polarization distributions of the head-to-head and tail-to-tail charged steps on the (100)-oriented 180 DWs in PTO and calculated the barriers for the motion of the steps

Summary

Introduction

Ferroelectric perovskites including BaTiO3, PbTiO3, and Pb(Zrx,Ti1-x)O3, have been widely studied in recent years because of their fascinating potential application in many ferroelectric devices, such as ferroelectric random access memories. It is known that the switching mechanism of the ferroelectric polarization, which essentially determines the performance of ferroelectric devices, is based on the movement of ferroelectric domain walls (DWs). Steps on the DWs play an important role in the mechanism underlying the DW motion with several switching models being proposed. Miller and Weinreich suggested that the motion of 180 DWs in BaTiO3 results from the repeated nucleation along existing parent DWs of triangular steps of one lattice-constant thickness. It is known that the switching mechanism of the ferroelectric polarization, which essentially determines the performance of ferroelectric devices, is based on the movement of ferroelectric domain walls (DWs).. Steps on the DWs play an important role in the mechanism underlying the DW motion with several switching models being proposed.. Miller and Weinreich suggested that the motion of 180 DWs in BaTiO3 results from the repeated nucleation along existing parent DWs of triangular steps of one lattice-constant thickness. With no consideration of the atomic-scale structure of the steps, the sharp steps of this model result in nucleation energies much higher than the experimental results.. Shin et al. demonstrated that a model with diffused steps does effectively decrease the nucleation energy yielding better agreement with experimental results than sharp steps. With no consideration of the atomic-scale structure of the steps, the sharp steps of this model result in nucleation energies much higher than the experimental results. Recently, Shin et al. demonstrated that a model with diffused steps does effectively decrease the nucleation energy yielding better agreement with experimental results than sharp steps.

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Results

Conclusion