Coexistence of Soft Modes and Dynamic Ti Disorder in Cubic BaTiO3 Studied by Inelastic Neutron Scattering

Abstract

The phonon dispersion relations in cubic BaTiO3 have been measured along the [100], [110], and [111] directions at T = 453 K using inelastic neutron scattering. The isotropic transverse acoustic (TA) branches indicate that the interatomic force constant between Ba and O atoms in BaTiO3 is large compared with that between Pb and O atoms in PbTiO3. The transverse optical (TO) branches along the [100] and [111] directions soften toward the Brillouin zone center. The TO branch along the [110] direction with [001] polarization is relatively low and flat, indicating the weak interatomic force constant between Ti and O atoms along the Ti–O chain. The intensity of inelastic diffuse scattering along the [100] and [110] directions increases with decreasing temperature down to 453 K. The present results suggest that the soft modes coexist with the dynamic Ti disorder in the Ti–O chain near the phase transition in the cubic phase.