Abstract
The relationship between birefringence and crystal structure in NaNbO3 is explained. In the antiferroelectric phases it is shown that the birefringence is a function of lattice strain and sublattice polarization, with the latter term providing the dominant contribution. The first term primarily arises out of the tilting of the anion octahedra and the second out of distortions of the octahedra induced by the off-centering of the B cations. In the paraelectric phases, in which only the tilts of oxygen octahedra are involved, the birefringence is shown to be a function of the lattice strains alone. The birefringence of PbZrO3 is also discussed briefly and compared with the results for NaNbO3.
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