Fig. 4: Phonon frequencies and relaxation times.

Frequencies and relaxation times were obtained from auto-correlation functions of a M-tilt and b R-tilt modes as a function of temperature. The shaded region indicates the overdamped regime. Note that the M-tilt mode is overdamped already about 200 K above the phase transition temperature. Here, markers are data points, and lines are interpolations to guide the eye.