LATTICE-DEFECTS IN SINGLE-CRYSTAL LITHIUM-NIOBATE .2. ELECTRIC-FIELDS OF DISLOCATIONS AND SMALL-ANGLE GRAIN-BOUNDARIES

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-LiNbO//3 suggest that they are responsible for the pinning of ferroelectric 180 degree domains of SAGBs lying in planes close to (0001). As poling fields (E//p approximately equals 10**3 V m** minus **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 the dislocations parallel to some crystallographic directions of high symmetry have no electric fields.