Interferometric studies of domain structures in potassium niobate single crystals

Interferometric studies of domain structures in KNbO 3 single crystals, grown by using excess of K 2 CO 3 as a flux are reported. The surface deformations produced on the pseudocubic (001) planes by the stable patterns of 90°, 60° and 180° domains have been studied and discussed. If the observed plane is not the plane of the shear, the 90° domains are inclined at 30prime. The angle between the 60° domains is 57prime for the domain line, parallel to a pseudocubic edge. The head to tail coupling of dipoles across the 60° domain walls gives a step ladder structure on the surface. The nature of dipole coupling in a step ladder due to 90° domains cannot, however, be distinguished. The wedges are all 60° wedges, with the wedge angle 57prime. The theoretical formulae have been derived, and the values found to agree closely with the experimental values. The angles between the planes and the other surface angles are all temperature dependent as they are functions of the lattice parameters. In the tetragonal phase, the domain behaviour is found to be quite similar to that of BaTiO 3 . The domain patterns are seen at times to have a memory indicating the presence of traps in the crystals for these domain walls.