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Analysis of quasielastic light scattering in LiTaO3 near TC

Analysis of quasielastic light scattering in LiTaO3 near TC,10.1103/PhysRevB.34.1880,Physical Review B,Ming-Sheng Zhang,J. F. Scott

Analysis of quasielastic light scattering in LiTaO3 near TC   (Citations: 1)
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We have reexamined the Raman spectra of lithium tantalate from 294 to 1059 K with special emphasis upon the quasielastic scattering from 0-200 cm-1. We show that the complete A1-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 chi-1(omega,T)=omega20(T)-omega 2-iomegagamma(T)-delta2(T)/[1-iomegatau(T)] and that the fitting parameters vary monotonically with temperature. In agreement with recent analysis of LiNbO3 [Okamoto, Wang, and Scott, Phys. Rev. B 32, 6787 (1985)] we find that the linewidth gamma for the lowest energy A1 phonon increases rapidly with temperature, from 27 cm-1 at 294 K to 382 cm-1 very near TC; tau exhibits a critical slowing down from 0.50 ps far from TC to 2.6 ps at TC and continues to increase above TC (5.3 ps at 1059 K); the lowest-energy optical phonon ``softens'' only slightly, from omega0 of 202 cm-1 at 294 K to 178 cm-1 at TC=881 K (determined from the dielectric constant), and that the coupling constant delta2(T) increases supralinearly with temperature, as in LiNbO3.
Journal: Physical Review B - PHYS REV B , vol. 34, no. 3, pp. 1880-1883, 1986
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