Acoustic Phonons In Transition-Metal Dichalcogenide Layer Compound Tise-2

The frequencies of acoustic phonons have been measured in the layer-type substance TiSe 2 by neutron inelastic scattering techniques. As expected from the two-dimensional nature of such substances the in-plane longitudinal sound velocity is much larger than that perpendicular to the layer, while the transverse mode propagating in the layer but polarised perpendicular to the layer exhibits an upwards curvature.