Abstract
We have reexamined the Raman spectra of lithium tantalate from 294 to 1059 K with special emphasis upon the quasielastic scattering from 0–200 . We show that the complete -symmetry spectrum at each temperature, including both the lowest-energy optical phonon and the quasielastic scattering, can be fitted to the response function for a system with a relaxing self-energy (ω,T)=(T)-ω -iωγ(T)-(T)/[1-iωτ(T)] and that the fitting parameters vary monotonically with temperature. In agreement with recent analysis of [Okamoto, Wang, and Scott, Phys. Rev. B 32, 6787 (1985)] we find that the linewidth γ for the lowest energy phonon increases rapidly with temperature, from 27 at 294 K to 382 very near ; τ exhibits a critical slowing down from 0.50 ps far from to 2.6 ps at and continues to increase above (5.3 ps at 1059 K); the lowest-energy optical phonon ‘‘softens’’ only slightly, from of 202 at 294 K to 178 at =881 K (determined from the dielectric constant), and that the coupling constant (T) increases supralinearly with temperature, as in .
- Received 18 February 1986
DOI:https://doi.org/10.1103/PhysRevB.34.1880
©1986 American Physical Society