Structural transformation of compressed solid Ar: An x-ray diffraction study to114GPa

Room temperature angle-dispersive x-ray diffraction measurements on solid Ar up to $114\mathrm{GPa}$ reveal evidence of a structural phase transformation after stress relaxation by laser heating. Beyond $49.6\mathrm{GPa}$, Ar exhibits the coexistence of fcc and hcp phases with an increasing hcp/fcc ratio, similar to the observation made recently on krypton and xenon. From the present results, we estimate the fcc-to-hcp transition to be completed at $300\mathrm{GPa}$.