SEARCH Articles Figures Tables 22 BaTiOs. Phonon dispersion relation determined by neutron scattering along the direction in the cubic phase, v is the phonon frequency. LA, longitudinal acoustic branch TA, transverse acoustic branch TO, transverse optical branch. The frequency of the TO branch is lower at 230 C than at 430 C, indicating mode softening [Publishers Imprint] See Also: 22 BaTiOs. Phonon dispersion relation determined by neutron scattering along the direction in the cubic phase, v is the phonon frequency. LA, longitudinal acoustic branch TA, transverse acoustic branch TO, transverse optical branch. The frequency of the TO branch is lower at 230 C than at 430 C, indicating mode softening