First-Order Raman Effect Induced by the Static Electric Field in Cubic Perovskite-Type Ferroelectrics
The first-order Raman effect in the paraelectric state of perovskite-type ferroelectrics induced by the field applied on the crystal in the direction of one crystallographic axis is investigated. Attention is paid mainly to the Cochran ferroelectric modes. First, the angular dependence of the Raman scattering efficiency S of these modes is derived when the incident (linearly polarized) and scattered light propagate perpendicularly to each other in the plane perpendicular to the applied field. Then, using the quasiharmonic approximation, S for ferroelectric modes is related to electro-optic constants and other measurable quantities. With a field of 1 kV/cm applied on the crystal, S equals 10-6-10-7 for BaTiO3 in the temperature range 120-150°C. The temperature dependence of this effect is discussed, and it is compared with the first-order Raman effect in the tetragonal phase of perovskite crystals.