Nonhydrostatic compression of elastically anisotropic polycrystals. I. Hydrostatic limits of 4:1 methanol-ethanol and paraffin oil

The compression of a foil of ${\mathrm{Cu}}_3\mathrm{Au}$ in 4:1 methanol-ethanol and paraffin oil pressure-transmitting media has been studied by energy-dispersive x-ray diffraction in a diamond-anvil cell. Line shifts and line profiles are used to analyze elastic and plastic strains. The increasing viscosity of 4:1 methanol-ethanol causes departures from hydrostatic conditions starting around 7 GPa even while the medium is in a liquid state. The glass transitions in the range 5–7 GPa for paraffin oil and 12–13 GPa for 4:1 methanol-ethanol cause a volume incompressibility and discontinuity followed by isotropic compression behavior. The hydrostatic limit of a liquid with respect to a polycrystalline sample may lie at pressures considerably below the pressure of solidification. For nonideal powders, even small departures from nonhydrostatic conditions of the pressure transmitting medium, often termed quasihydrostatic, can have a strong influence on the compression behavior.