Phonon dispersion curves in an argon single crystal at high pressure by inelastic x-ray scattering

The phonon dispersion of fee argon under high pressure to 20 GPa has been measured along the (100) direction by inelastic x-ray scattering. First, this shows a novel possibility to investigate the single crystal dynamical properties under very high pressure in a diamond anvil cell. Second, the comparison between experiment and phonon calculations, using pair potentials (either the pure two-body potential or an effective pair potential) and a Slater-Kirkwood form for the three-body interaction, clearly demonstrates that phonon energies can be strongly influenced under high pressure by the nonadditive part of the interaction.