Defects in motion

Abstract

Crystalline defects appear when the perfect order of the lattice or ideal arrangements of atoms, molecules, or ionic groups is destroyed, which is inevitable during crystal growth, thereby impacting material functionalities, either in a reinforcing or unwanted way. For functional ferroic materials, natural interfaces called domain walls form, which separate regions of different orientations of a specific order (such as magnetic, ferroelastic, or ferroelectric) in the material. These, including phase boundary, grain boundary, and/or domain boundary, can be reckon as two-dimensional defects. During functioning of ferroic materials, phase transformation and/or dynamic motion of domain walls occur with external stimuli like electric fields or stress. Therefore, domain engineering, phase boundary construction, and grain engineering has long been the most considered effective strategies to enhance the performance of ferroic materials. Meanwhile, lower-dimensional defects, including point defects, defect dipole, and line defects, are another crucial dimension to be considered to tune functionality, since their motion greatly interact with the domain wall dynamics under external stimuli. In all, defect engineering (here we refer to one- and two-dimensional defects) and its coupled motion with order parameters is an interesting topic that has attracted significant attention for functional oxides.