Anharmonic effects in LHP- and LDP-type ferroelectrics, investigated with the Green‘s function technique

Abstract

A Green‘s function technique is used to study the anharmonic pseudo-spin-phonon and phonon-phonon interaction effects in LHP and LDP-type ferroelectrics on optical phonon mode frequency, damping and transverse dynamical structure factor below and above T_c. The coupling between the transverse soft-mode and the optical phonon mode produces a central peak in the transverse dynamical structure factor. The temperature dependence of these quantities is discussed and it is in good agreement with the experimental data. At low temperatures the contribution of the anharmonicity is very small, but at temperatures near the critical temperature T_c and above T_c it increases strongly.

Key Words:

• Anharmonic effects, central peak, H-bonded ferroelectrics, dynamical structure factor