Thermodynamic properties of liquid gallium from picosecond acoustic velocity measurements.

Due to discrepancies in the literature data the thermodynamic properties of liquid gallium are still in debate. Accurate measurements of adiabatic sound velocities as a function of pressure and temperature have been obtained by the combination of laser picosecond acoustics and surface imaging on sample loaded in diamond anvil cell. From these results the thermodynamic parameters of gallium have been extracted by a numerical procedure up to 10 GPa and 570 K. It is demonstrated that a Murnaghan equation of state accounts well for the whole data set since the isothermal bulk modulus BT has been shown to vary linearly with pressure in the whole temperature range. No evidence for a previously reported liquid-liquid transition has been found in the whole pressure and temperature range explored.

Picosecond acoustics method for measuring the thermodynamical properties of solids and liquids at high pressure and high temperature.

Based on the original combination of picosecond acoustics and diamond anvils cell, recent improvements to accurately measure hypersonic sound velocities of liquids and solids under extreme conditions are described. To illustrate the capability of this technique, results are given on the pressure and temperature dependence of acoustic properties for three prototypical cases: polycrystal (iron), single-crystal (silicon) and liquid (mercury) samples. It is shown that such technique also enables the determination of the density as a function of pressure for liquids, of the complete set of elastic constants for single crystals, and of the melting curve for any kind of material. High pressure ultrafast acoustic spectroscopy technique clearly opens opportunities to measure thermodynamical properties under previously unattainable extreme conditions. Beyond physics, this state-of-the-art experiment would thus be useful in many other fields such as nonlinear acoustics, oceanography, petrology, in of view. A brief description of new developments and future directions of works conclude the article.

Equation of state of liquid mercury to 520 K and 7 GPa from acoustic velocity measurements.

Ultrafast acoustics measurements on liquid mercury have been performed at high pressure and temperature in a diamond anvil cell using picosecond acoustic interferometry. We extract the density of mercury from adiabatic sound velocities using a numerical iterative procedure. We also report the pressure and temperature dependence of the thermal expansion, isothermal and adiabatic compressibility, bulk modulus, and pressure derivative of the latter up to 7 GPa and 520 K. We finally show that the sound velocity follows a scaling law as a function of density in the overall measured metallic state.

Diffusionless γ⇄α phase transition in polycrystalline and single-crystal cerium.

The cerium γ⇄α transition was investigated using high-pressure, high-temperature angle-dispersive x-ray diffraction measurements on both poly- and single-crystalline samples, explicitly addressing symmetry change and transformation paths. The isomorphic hypothesis of the transition is confirmed, with a transition line ending at a solid-solid critical point. The critical exponent is determined, showing a universal behavior that can be pictured as a liquid-gas transition. We further report an isomorphic transition between two single crystals (with more than 14% of volume difference), an unparalleled observation in solid-state matter interpreted in terms of dislocation-induced diffusionless first-order phase transformation.

Liquid mercury sound velocity measurements under high pressure and high temperature by picosecond acoustics in a diamond anvils cell.

Recent improvements to measure ultrasonic sound velocities of liquids under extreme conditions are described. Principle and feasibility of picosecond acoustics in liquids embedded in a diamond anvils cell are given. To illustrate the capability of these advances in the sound velocity measurement technique, original high pressure and high temperature results on the sound velocity of liquid mercury up to 5 GPa and 575 K are given. This high pressure technique will certainly be useful in several fundamental and applied problems in physics and many other fields such as geophysics, nonlinear acoustics, underwater sound, petrology or physical acoustics.

Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in a diamond anvil cell: application to the stability study of AlPdMn.

We report an innovative high pressure method combining the diamond anvil cell device with the technique of picosecond ultrasonics. Such an approach allows us to measure sound velocity and attenuation of solids and liquids under pressure of tens of GPa, overcoming all the drawbacks of traditional techniques. The power of this experimental technique is demonstrated in studies of lattice dynamics and relaxation processes in a metallic single grain of AlPdMn quasicrystal, and in rare gas solids neon and argon.

Study of the invar effect through ultrasonic measurements of the elastic properties of Fe(64)Ni(36) under pressure.

The elastic properties of a polycrystalline sample of invar Fe(64)Ni(36) have been investigated at ambient temperature by ultrasonic experiments up to 7 GPa. The pressure dependence of the bulk modulus is extracted without using any model and discussed in terms of invar anomaly models.

Accurate equation of state of AlPdMn up to 35 GPa and pressure effect on the frozen-in phason strain.

Angle-dispersive monochromatic x-ray diffraction spectra from a perfect single-grain AlPdMn quasicrystal have been obtained under hydrostatic pressure in a diamond anvil cell up to 35 GPa. More than 50 Bragg peaks with sharpness comparable to that at ambient conditions were observed up to the maximum pressure, indexed and used to measure the hypercubic 6D lattice parameter, providing the most accurate determination of the equation of state in this pressure range to date. Within the instrumental resolution, the absence of broadening of the diffraction peaks indicates the absence of structural transition and/or unusual configurational entropy change expected from previous studies through pressure-induced amorphization or phason defects.

Ultrasonics and X-ray diffraction under pressure in the Paris-Edinburgh cell

Our objective consists in validating a new set-up which will permit us to carry out simultaneously ultrasonic and X-ray diffraction measurements under pressure. To validate the results obtained by this new set-up, the elastic properties of a single crystal of germanium were studied. Our results are in good agreement with those of Goncharova et al. and McSkimin and Andreatch. The results of the present study are compared with those of Menoni et al. and obtained by X-ray diffraction in a diamond anvil cell.