TEMPERATURE-DEPENDENCE OF E-SYMMETRY PHONON-POLARITONS IN PBTIO3

We have studied in the temporal domain E-symmetry phonon-polaritons of PbTiO3 perovskite. Their dependence as a function of temperature is i nvestigated up to the ferroelectric phase transition to cubic symmetry . Knowledge of the behaviour of the two lowest polariton branches allo ws us to estimate accurately their oscillator strength evolution. The values deduced for the static dielectric constant are in agreement wit h spectral domain values obtained using the Lyddane-Sachs-Teller relat ion but not with those from capacitance measurements performed at 1 KH z and I MHz.