Lattice Dynamics of Tantalum

The frequency-wave-vector dispersion relation (ν(q)) for lattice waves traveling in the [00ζ], [ζζ0], and [ζζζ] symmetric directions of tantalum has been measured at 296^∘{}K, using methods of neutron inelastic scattering. The results show strong similarities with the previously measured ν(q) for niobium. The results can be fitted by a Born-von K\'arm\'an force model only if very long-range forces are invoked. Because of the peculiar nature of ν(q), the Debye approximation appears to be better for tantalum than for most other materials.