Lattice defects in single-crystal lithium niobate II. Electric fields of dislocations and small-angle grain boundaries

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Abstract
The elastic stresses of small-angle grain boundaries (SAGBs) in non-centrosymmetrical crystals produce electric fields due to the piezoelectric effect. Calculations of these fields for YZ-LiNbO3 suggest that they are responsible for the pinning of ferroelectric 180° domains to SAGBs lying in planes close to (0001). As poling fields (Ep≈.103 Vm−1) are generally two orders of magnitude smaller than the electric field of the SAGB, no polarization reversal takes place and ferroelectric domains remain in the crystal. Attention is paid to the fact that dislocations parallel to some crystallographic directions of high symmetry have no electric fields. These dislocations would show a different interaction with 180° domains. So far this has not yet been observed in lithium niobate but should be taken into account when ferroelectrics belonging to other point groups are investigated.