Polariton Results in Ferroelectrics with the Tungsten Bronze Crystal Structure

Abstract

Measurements are presented as a function of temperature, in several ferroelectric crystals with the tungsten bronze crystal structure, using forward Raman scattering (polaritons). These results determine the frequencies of TO and LO modes. Thus, the strengths of the optic modes and the frequency dependence of the dielectric constant ε(ω) can be determined. From these results, the low‐frequency clamped dielectric constant ε(0) surprisingly is found to be approximately independent of temperature to T_c. We believe that the results indicate that these ferroelectrics do not have ``soft'' optic modes in the usual sense but are relaxers.