Soft mode in cubic PbTiO3 by hyper-Raman scattering

Hyper-Raman scattering experiments allowed collecting the spectra of the lowest F-1u-symmetry mode of PbTiO3 crystal in the paraelectric phase up to approximate to 930 K as well as down to about 1 K above the phase transition. It is realized that this mode is fully responsible for the Curie-Weiss behavior of its dielectric permittivity above T-c. Near the phase transition, this phonon frequency softens down to 17 cm(-1) and its spectrum can be well modeled as a response of a single damped harmonic oscillator. It is concluded that PbTiO3 constitutes a clean example of a soft-mode-driven ferroelectric system. DOI: 10.1103/PhysRevB.87.064101