A CHANGE IN DOMAIN MORPHOLOGY IN OPTICAL SUPERLATTICE LINBO3 INDUCED BY THERMAL ANNEALING

Optical superlattice LiNbO3 crystals were grown by the Czochralski met hod. The effect of thermal annealing below the Curie temperature on do main structures of a sample with good periodicity was studied. II was found that the periodic domain structure remained unchanged at anneali ng temperature lower that 1000 degrees C and began to deteriorate when annealed at above 1000 degrees C. A sample at 1100 degrees C for an h our almost changed to a single-domain structure except that a 60 mu m single-domain layer with reversed spontaneous polarization was formed at the edge of the sample. These results are useful for revealing the mechanism of formation of the periodic domain structure and designing a more favourable temperature field to improve the crystals' quality. A space-charge-field model was proposed to explain the phenomena.