• B M Bangre

      Articles written in Pramana – Journal of Physics

    • Domain structure in ferroelectric PbNb2O6

      S G Ingle B M Bangre

      More Details Abstract Fulltext PDF

      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$$\left( {\bar 110} \right)$$ 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.

    • Domain formation inside thick crystals of ferroelectric PbNb2O6

      S G Ingle B M Bangre

      More Details Abstract Fulltext PDF

      Stress dependence of domains in thick crystals of PbNb2O6 is reported. Successive etching shows numerous domains in the bulk not extending to the surface. These domains have correlation with the dislocation substructure in the bulk. The dislocations are in the form of small loops, and domain walls are found terminating along with these loops. The general problem of volume nucleation is discussed, and it is suggested that these dislocation loops play a significant role in domain formation.

    • Optical, etching, and interferometric studies on ferroelectric PbNb2O6

      S G Ingle B M Bangre

      More Details Abstract Fulltext PDF

      Optical, interferometric and etching studies of (001) surfaces of ferroelectric PbNb2O6 are presented. It is found that crystal growth takes place mainly by layer formation. The layer boundaries can be distinguished from the domain lines by interferometric studies. Thermal etch pits are found near 90° domain walls and the layer boundaries. The etching studies show that these pits are at the sites of dislocations, and it is deduced that no extensive motion of dislocation takes place at the Curie-temperature in the process of domain formation.

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