Anomalous Increase in Spectral Intensity of Soft-Mode Raman Scattering near the Temperature of the Ferroelectric Phase Transition in Lithium Tantalate Crystals

Abstract

Reported are the results of studying the sharp increase in the spectral intensity at the lattice soft mode near the temperature of the phase transition in the lithium tantalate crystal. The Raman scattering spectra are recorded in the x(zz)y polarization geometry corresponding to manifestation of the soft mode responsible for the ferroelectric phase transition in lithium tantalate at 898 K. The recording is performed at fixed temperatures T ( $$I(\omega {\kern 1pt} ',T)$$ , T = const) and at fixed spectrometer frequencies ( $$I(\omega {\kern 1pt} ',T)$$ , $$\omega {\kern 1pt} ' = {{\omega }_{0}} - T = {\text{const}}$$ ) under slow (1 deg./min) crystal temperature variation. Strong increase (by three orders of magnitude) is observed in the peak of the reduced spectral intensity i0(Ω) of the isofrequency temperature dependence at the fixed spectrometer frequency shift relative to the exciting radiation $$\Omega = {{\omega }_{0}} - \omega {\kern 1pt} ' = 10$$ cm–1 similar to the one earlier observed in quartz crystals.