Lattice dynamics of argon at 4 degrees K

Neutron scattering techniques have been used to measure the phonon dispersion relations in a single crystal of 36Ar at 4 degrees K. Data have been taken along the (110) and the (111) crystallographic directions. The analysis is expressed in terms of a two-neighbour force-constant model with five disposable parameters; one linear combination of three of these parameters is not determined well by the data. It is shown that the measurements are not inconsistent with a Mie-Lennard-Jones potential where the parameters are determined entirely from other macroscopic measurements on argon. However, there is a discrepancy with recent measurements of the elastic constants.