Melting curve and fluid equation of state of carbon dioxide at high pressure and high temperature

Accepted by Journal of Chemical Physics; in pressThe melting curve and fluid equation of state of carbon dioxide have been determined under high pressure in a resistively-heated diamond anvil cell. The melting line was determined from room temperature up to $11.1\pm0.1$~GPa and $800\pm5$~K by visual observation of the solid-fluid equilibrium and in-situ measurements of pressure and temperature. Raman spectroscopy was used to identify the solid phase in equilibrium with the melt, showing that solid I is the stable phase along the melting curve in the probed range. Interferometric and Brillouin scattering experiments were conducted to determine the refractive index and sound velocity of the fluid phase. A dispersion of the sound velocity between ultrasonic and Brillouin frequencies is evidenced and could be reproduced by postulating the presence of a thermal relaxation process. The Brillouin sound velocities were then transformed to thermodynamic values in order to calculate the equation of state of fluid CO$_2$. An analytic formulation of the density with respect to pressure and temperature is proposed, suitable in the $P-T$ range 0.1-8~GPa and 300-700~K and accurate within 2\%. Our results show that the fluid above 500 K is less compressible than predicted from various phenomenological models

Equations of State of Simple Solids (Including Pb, NaCl and LiF) Compressed in Helium or Neon in the Mbar Range

The equations of state measured under ambient temperature in the Mbar range are reviewed, focusing on experiments using diamond anvils cells with a quasi-hydrostatic pressure transmitting medium (helium or neon) and coupled with X-ray diffraction. Equations of state (EoS) parameters are listed with an unified pressure metrology for all data. This metrology is based on the efforts made in the 2000s to update the ruby luminescence pressure scale, after the collection of original data. To complete this database, unpublished P-V data for lead (Pb), sodium chloride (NaCl) and lithium fluoride (LiF) are also provided with the same metrology. Systematic effects of the pressure metrology on the EoS parameters are discussed

Phase transitions and equation of state of zirconium under high pressure

X-ray diffraction measurements performed in a diamond anvil cell under quasihydrostatic conditions up to 142 GPa at 300 K evidence an α-Zr → (17 GPa) ω-Zr → (35 GPa) β-Zr phase transitions sequence. Ab initio molecular dynamics calculations performed on the body-centered cubic β-Zr at 300 and 1000 K and between 0 and 100 GPa produced an equation of state in excellent agreement with the experiments. The stability of β-Zr under pressure has been verified by numerical heating-quenching experiments, and the anharmonicity of the thermal vibrations has been evaluated. No dynamical instability due to a soft mode is evidenced between 25 and 100 GPa, in line with the experimental finding of a wide stability range for β-Zr

P-V-T equation of state of periclase from synchrotron radiation measurements

International audienceThe volume of periclase (MgO) has been measured by monochromatic X-ray diffraction in a laser-heated diamond anvil cell up to a pressure of 53 GPa and a temperature of 2500 K. The X-ray source was synchrotron radiation at the European Synchrotron Radiation Facility (Grenoble, France). In addition to laser heating, the use of argon as a pressure transmitting medium provided quasi-hydrostatic conditions in the cell assembly. In order to take thermal pressure effect into account, pressure was measured using an internal pressure calibrant (platinum). By analysis of the experimental P-V-T data set the following parameters were obtained: at ambient temperature, K'0 = 3.94 ± 0.2 when K0 is fixed to 161 GPa (with a Birch-Murnaghan equation of state); under high temperature, α(P = 0,T) = (3.0 + 0.0012T) × 10-5 K-1; (∂KT/∂T)P = -0.022(3) GPa K-1. The quasi-harmonic Debye model appears to describe correctly the temperature dependence of the volume at high pressure within experimental errors, with the following parameters: θD0 = 800 K, γ0 = 1.45 (Grüneisen parameter under ambient conditions), and q = 0.8 ± 0.5

Toroidal diamond anvil cell for detailed measurements under extreme static pressures

Extreme static pressures exceeding a million atmospheres exist in a variety of natural environments, but obtaining such pressures in a laboratory is still a challenge. Here, the authors develop a toroidal diamond anvil design that allows for the generation of 600 GPa (6 million atmospheres) in routinely used diamond anvil cells

Xenon and Argon: A contrasting behavior in olivine at depth

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Following the phase transitions of iron in 3D with X-ray tomography and diffraction under extreme conditions

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