F. Decremps

Trapping of cubic ZnO nanocrystallites at ambient conditions

Dense powder of nanocrystalline ZnO has been recovered at ambient conditions in the metastable cubic structure after a heat treatment at high pressure (15 GPa and 550 K). Combined x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) experiments have been performed to probe both long-range order and local crystallographic structure of the recovered sample. Within uncertainty of these techniques (about 5%), all the crystallites are found to adopt the NaCl structure. From the analysis of XRD and XAS spectra, the cell volume per chemical formula unit is found to be 19.57(1) and 19.60(3) A3, respectively, in very good agreement with the zero-pressure extrapolation of previously published high-pressure data.

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.

Equation of state, stability, anisotropy and nonlinear elasticity of diamond-cubic (ZB) silicon by phonon imaging at high pressure

Experimental phonon imaging in diamond anvils cell is demonstrated to be an adequate tool to extract the complete set of elastic constants of single-crystalline silicon up to the ZB ->beta-Sn transition (10 GPa). Contrary to what was commonly admitted, we demonstrate that the development of the strain-energy density in terms of strains cannot be stopped, for silicon, after the terms containing the third-order elastic constants. Nonlinear elasticity, degree of anisotropy and pressure-induced mechanical stability of the cubic silicon structure are thus revisited and investigated in more detail.

Sound velocity of iron up to 152 GPa by picosecond acoustics in diamond anvil cell

High-pressure method combining diamond anvil cell with picosecond ultrasonics technique is demonstrated to be a very suitable tool to measure the acoustic properties of iron up to 152 GPa. Such innovative approach allows to measure directly the longitudinal sound velocity under pressure of hundreds of GPa in laboratory, overcoming most of the drawbacks of traditional techniques. The very high accuracy, comparable to piezoacoustics technique, allows to observe the kink in elastic properties at the body-centered cubic–hexagonal close packed transition and to show with a good confidence that the Birchs law still stands up to 1.5 Mbar and ambient temperature. The linear extrapolation of the measured sound velocities versus densities of hcp iron is out of the preliminary reference Earth model, arguing for alloying effects or anharmonic high-temperature effects. A comparison between our measurements and shock wave experiments allowed us to quantify temperature corrections at constant pressure in ~−0.35 and ~−0.30 m s−1/K at 100 and 150 GPa, respectively. More in general, the here-presented technique allows detailed elastic and viscoelastic studies under extreme thermodynamic conditions on a wide variety of systems as liquids, crystalline, or polycrystalline solids, metallic or not, with very broad applications in Earth and planetary science.

High-pressure ultrasonic setup using the Paris–Edinburgh press: Elastic properties of single crystalline germanium up to 6 GPa

A setup for the measurement of ultrasonic properties of single crystals at high pressure in the 10 GPa range is presented. In order to validate this new device, based on the “Paris–Edinburgh” press, the elastic properties of germanium have been measured and compared with the published data. The transit times of the ultrasonic waves are directly measured. The three elastic moduli and their pressure derivatives are obtained up to 6 GPa through three different methods of calculation, which are presented and compared. These results are in good agreement with previous results and hence validate the device. The Paris–Edinburgh press enables in situ measurement of ultrasonic and x-ray diffraction on the studied sample.

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.

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.

Structure of crystalline and amorphous Ge probed by X-ray absorption and diffraction techniques

Results of experiments dedicated to the study of the structure under high pressure of amorphous Ge (a-Ge) and crystalline Ge (c-Ge) are reported. Energy-dispersive X-ray diffraction measurements of c-Ge have been collected at the DW11A beamline (DCI, LURE) using a heatable diamond anvil cell as pressure device up to 500 K. The a-Ge measurements have been performed at the ESRF, using the advanced set-up available at the BM29 beamline, which allows the simultaneous collection of X-ray absorption spectroscopy data and diffraction patterns used to monitor pressure and crystallization of a sample in a Paris–Edinburgh large-volume cell. The new structural data allowed us to obtain a reliable determination of the lattice parameters as a function of pressure and temperature in c-Ge and of the first-neighbor distance distribution in a-Ge.

Some scaling factors of physical properties dependent on phonons in the case of the families of the fluorite and of the matlockite

Abstract The evolution of some physical properties which are linked to the phonons, like some infrared and Raman frequencies, the elastic constants and the Debye temperatures, in the related families of the fluorite (CaF 2 ) and the matlockite (PbFCl) is made easier by the use of the scaling factors. In these two families, the arrangement of the metal (M) and the fluorine (F) ions is similar and only the interactions between M and F are taken into account. It is postulated that the order of magnitude of these interactions remains the same for both families. In this condition, the scaling factors, deduced from the shell-model formulae, depend mainly on structural considerations. So the invariability of the M-F short-range interactions through the whole families and the independence of some physical properties in consideration of the other short-range interactions, together with their evolution and their order of magnitude are analysed by means of the scaling factors. Finally, these can be used as a test of the phonon models.

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.