An unusual electrical response of dislocations and impurity dipoles in monocrystals was reported. The etch pits which disclosed these defects moved in the structure and carried the defects with them. This showed that the defects had associated with them structural units that were orders of magnitude larger in size. These units were also associated with stress fields and electric effects, because of the ferroelectric nature of the crystal. The nature of the stress fields could be determined by studying the movement of the etch pits under an applied electric field. It was found that impurity dipoles in the pseudo-cubic (001) surface had stress fields which were similar to those of screw dislocations, and dipoles in the front and side faces had stress fields that were similar to those of edge dislocations. An external direct-current field caused rotation of the dislocation loops, and therefore changed the domain structure. It could order or disorder the dislocations, and the effect was reversible. Similar effects were observed in the case of impurity dipoles. Several consequences of the stress fields were considered theoretically and observed experimentally. Thus, the stress fields of impurity dipoles and dislocation loops led to their mutual exclusion. At a given point in the crystal, the domain structure was nucleated either by dislocation loops or by impurity dipoles. Conjoined domain nucleation by an impurity dipole and a dislocation loop was predicted on theoretical grounds and observed experimentally. Long-range mutual interaction, bulk ordering, dependence of the bulk ordering upon the defect density, and domain nucleation, were explained in terms of the structural units which were associated with the impurity dipoles and dislocation loops.

S.G.Ingle, R.N.Kakde: Journal of Applied Physics, 1995, 78[1], 104-10