Domain structure in ferroelectric PbNb2O6

Single crystals of ferroelectric PbNb₂O₆ were grown employing a modification of the technique of Goodman. The results obtained on the domain structure were analysed and compared with those reported on BaTiO₃ and KNbO₃. The domain structure observed here corresponds to the twinning on (110) plane of the unit cell reported by Francombe and Lewis or the subcell reported by Labbe and others. The (001) planes were observed, as the crystal habit is such as to produce (001) planes, and the cleavage plane is also (001). Also the analysis of the observations can be done easily under these conditions. The domains observed are 90° domains with polar axis in (001) plane. Wedge shaped domains and spikes are present as in BaTiO₃ and KNbO₃. The twinning can occur also on plane producing a domain line at 90° with that due to twinning on (110). This gives patterns of perpendicular lines similar to those in KNbO₃ and BaTiO₃. Crystal structure considerations show that the domain structures with polarization in and out of the observed (001) plane are not possible, and also were not observed. In this sense, it is a two dimensional ferroelectric. The studies showed a peculiar grain structure in the crystals, and it can be explained on the basis of the growth habit of the crystal. The polarizing microscope is particularly useful in analysing the domain structure along with the grain structure.