Domain-impurities interaction in KNbO3 single crystals

Abstract

Impurity segregations and their interactions with domains and dislocations in KNbO3 single crystals have been studied. In the technique used, impurity structures in the bulk are first brought to the surface by removing layers of crystal without stress by methyl alcohol. The domain structure in the crystal remains completely undisturbed in this process. The dislocation pattern is then revealed by etch pits produced with an etchant such as a mixture of a concentrated solution of ammonium acetate in water and hydrogen peroxide (30% wt/vol) in the volume ratio 1 : 2. It has been found that impurity segregations interfere quite appreciably with domain formation. Segregations around arrays of edge dislocations form surprisingly straight lines parallel to pseudocubic 〈100〉 directions, appearing very similar to 60° domain lines under reflected light. Under these conditions, they prevent the formation of a 60° domain. Domain walls terminate at such lines, and may also be bent as a result of segregation-dislocation interactions, occupying crystallographically irregular positions. These and other observations are discussed, providing the necessary microscopic and interferometric evidence.