Polarization-Dependent Rayleigh Scattering in a Coarse-Grained Ferroelectric Ceramic

Publisher Website
Google Scholar
Abstract
Visible light intensity transmitted by a polarized ferroelectric crystallite of diameter ≥2 μ has been observed to decrease markedly when the direction of polarization Ps is shifted from parallel to perpendicular to the direction of incidence. This is explained by regarding the 180° domain structure as constituting a displacement field, in which ions are shifted relative to a cubic reference phase. The Fourier wavevectors of this field shift with Ps, causing an increase in backscattering when Ps is normal to the light. This property is demonstrated for tetragonal, orthorhombic, and rhombohedral phases of a perovskite, and in all cases scattered intensity is proportional to Ps4. Selection rules affecting depolarization of the light are derived from the polarizability theory of Raman processes. This theory supposes that the incident radiation polarizes the atoms, which then emit dipole radiation whose amplitude is proportional to the polarizability α. The latter depends on the displacement field whose symmetry, combined with the cubic symmetry of the reference phase, requires certain tensor components of α to vanish. This imposes no important limits on backscattering, but it predicts that α should be isotropic in the rhombohedral phase, thus preventing the domain structure from providing a significant source of forward depolarization. Grain‐boundary scattering and reflections must be invoked to explain the latter.