Elastic Constants of Argon at 4.2 °K from Phonon Measurements

Phonon measurements with inelastic neutron scattering have been analysed carefully, by use of the resolution ellipsoids of the three‐axis spectrometer. The slopes of the dispersion curves at the low frequency phonons are taken to be the sound velocities. From these sound velocities the elastic constants are calculated: C 11 = (3.67 ± 0.14).10 10 dyn cm −2 , C 12 = (1.74 ± 0.17).10 10 dyn cm −2 , C 44 = (2.34 ± 0.11).10 10 dyn cm −2 . Theoretical calculations with an accurate pair potential in the self‐consistent phonon approximation give the best agreement for a model without anharmonicity and without three‐body forces.