Atomic coordinates and polarization map around a pair of 1/2a[011] dislocation cores produced by plastic deformation in relaxor ferroelectric PIN-PMN-PT

摘要

The core structures of dislocations are crucial for understanding the plastic deformation mechanisms and the functional properties of materials. Here, we use the scanning transmission electron microscopy imaging techniques of high-resolution high angle annular dark field and integrated differential phase contrast to investigate the atomic structure of a pair of climb-dissociated 1/2a[011] dislocations in a bending-deformed relaxor ferroelectric Pb(In_(1/2)Nb_(1/2))O_3-Pb(Mg_(1/3)Nb_(1/3))O_3-PbTiO_3 single crystal. Cations at one dislocation core are found to arrange in the same way as the climb-dissociated 1/2a[011] dislocation core in SrTiO_3, while the other one is different. Oxygen depletion was observed at both dislocation cores. Geometric phase analysis of the lattice rotation shows opposite signs at both sides of the dislocations, demonstrating the strain gradient, which is known to give rise to flexoelectric polarization. Using the peak finding method, the polarization (a combination of ferroelectric and flexoelectric) around dislocations was mapped at the unit-cell scale. The polarization direction obtained is consistent with that predicted based on the flexoelectric effect in a perovskite oxide with [011] geometry. Head-to-head positively charged and tail-to-tail negatively charged domain walls were revealed based on the polarization map, suggesting a new way to stabilize charged domain walls via dislocations. A distinct dislocation core configuration has been observed, and a unit-cell scale polarization map helps understand the flexoelectric effects (coupling between strain gradient and polarization) around dislocations in a relaxor ferroelectric.