Lattice Vibrations of Thallium at 77 and 296 K

Lattice vibration frequencies of Tl at 77 and 296 K have been measured along the lines Δ and Σ by neutron inelastic scattering. Modified axially symmetric force-constant models were fitted to the neutron data and were used to calculate phonon-dispersion curves along other symmetry directions in the crystal. Frequency distributions calculated from the 77-K models are compared with the results of superconducting tunneling experiments of Clark and Dynes.