Lattice vibrations of Bi2Te3

The dispersion curves for phonons propagating along the trigonal axis of the layer-structure emiconductor Bi2Te3 at 77 K have been determined by coherent inelastic neutron scattering techniques. Analysis of these results in terms of a simple interplanar force model shows a) that the forces between adjacent planes of Te atoms are comparable to those between nearest neighbour planes of Bi and Te and b) that foreces between next-nearest-neighbour planes have to be considered. In addition, a limited number of phonons were measured at 300 K and some low-frequency modes propagating along the bisectrix within the planes were determind. The results are compared, where possible, with previous Raman scattering, infrared reflection, and elastic constant measurements.