Elastic constants of argon single crystals determined by Brillouin scattering

Single crystals of argon were grown and investigated at 82.3 K, near the triple point. X-ray diffraction photographs taken in transmission were used to verify that the crystals were single and to determine their orientation. Brillouin spectra were obtained for several different orientations of three crystals. The observed spectra contained the longitudinal component and at least one, and sometimes both transverse components. Their frequency shifts were used to determine the adiabatic elastic constants at 82.3 K: C₁₁=2.38±0.04, C₁₂=1.56±0.03, C₄₄=1.12±0.03, in units 10¹⁰ dyn/cm², and the elastic anisotropy A=2.73±0.10. These values differ significantly from earlier results derived from neutron scattering and ultrasonic experiments. However, there is good agreement with recent Monte Carlo calculations which use multiparameter pair potentials and the triple-dipole interaction.