Raman Scattering in Small Crystals

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Abstract
The Raman scattering of a powder composed of small crystals of a noncentrosymmetric ionic material is considered using the Nyquist-theorem approach of Barker and Loudon. For modes that are both Raman and infrared active, the splitting of the transverse- and longitudinal-phonon frequencies is determined by the local electric field. This local field depends on the shape of the particles and on the power density. The relative contribution to the Raman scattering from macroscopic electric field fluctuations and from atomic displacement fluctuations is also dependent on the powder density. This effect yields an antiresonance in the Raman intensity scattered by longitudinal phonons.