Lattice dynamics of PbTiO3

Abstract

Inelastic neutron scattering experiments were performed to investigate the phonon dispersion relations along the [1,0,0], [1,1,0] and [1,1,1] directions in cubic PbTiO3. All of the transverse optic (TO) branches soften significantly toward the zone center around Tc. The zone-center TO mode stiffens considerably at 1173 K. The energies of the [ξ, 0, 0] TO branch for PbTiO3 measured at 793 K are considerably higher than those for Pb(Zn1/3Nb2/3)O3 at 423 K in the entire zone. The [ξ, 0, 0] transverse acoustic (TA) branch is found to soften slightly at 793 K. The [ξ, ξ, ξ] TA branch exhibits two minima at the middle point (1/4,1/4,1/4) and the zone boundary (1/2,1/2,1/2). These two modes are weakly temperature dependent up to 1173 K.