Application of domain wall nucleation to purification of KNbO3 single crystals

A technique for purifying KNbO₃ crystals by driving out impurities that exist in the form of dipoles and stabilizing them by forming microdomains at the Curie temperature was developed. The crystals were subjected to DC fields of 7.5 kV-cm^-1 for 10 min. In the process, fresh favorably oriented microdomains were nucleated and the crystal contained almost complete microdomains favorably oriented to the applied DC field. The reverse DC field of about 12 kV-cm^-1 was then applied for 2 min. This evaporated most of the microdomains as they were unfavorably oriented, but the fresh microdomains were not formed as the field was applied for a short duration. The dipoles tend to relax to the ionic state and were conducted away to one of the major surfaces, from which they can be washed away. The repeated application of the procedure results in the crystal being significantly purified