High pressure equation of state studies using methanol-ethanol-water and argon as pressure media

We have measured the equation of state of the intermetallic compound AuIn₂ up to 20 GPa and Cd_0.8Hg_0.2 up to 50 GPa using methanol-ethanol-water solution or argon as pressure media. In the experiments performed with argon as pressure medium, we minimized non-hydrostatic conditions by thermally annealing the sample. We present data revealing compressibility anomalies in AuIn₂ at 2.7 GPa and in Cd_0.8Hg_0.2 near 8, 18 and 34 GPa with methanol-ethanol-water and argon. At pressures above 5 GPa the P-V data for AuIn₂ and Cd_0.8Hg_0.2 from experiments preformed with argon as a pressure medium start deviating from those using methanol-ethanol-water, and the equation of state based on experiments in argon is stiffer compared with that in methanol-ethanol-water. This behavior is consistent with the relative merits of the two pressure transmitting media as documented in the literature. We also provide a brief summary of the results of electronic structure calculations that associate these anomalies with electronic topological transitions.     

Test of a high pressure equation of state

An equation of state for shock compressed matter is used to correlate P.V.T. data for Ag, Cu, Mo, Pd and K in the range from 0.05 to 0.95 M bar. Isotherms at 293K are obtained and the results are compared with static experimental data. Very good agreement between calculated and experimental values is generally obtained for all the materials considered. A critical analysis of the data is presented.     

Properties of solid argon under pressure

By using an improved nonsymmetric approximation of a self-consistent field for strongly anharmonic crystals and taking account of the anharmony to the sixth order, thermodynamic properties of solid argon were calculated in broad limits of the external parameters. Both the multiparametric pairwise potential of Barker and co-workers, and the 126 model potential of Lennard-Jones were used. The three-particle Axelrod-Teller-Muto forces were taken into account. A simple temperature dependence is obtained for the pressure and the isothermal elastic modulus. The results of the computations are compared with experimental data. The best agreement is assured by the Barker-Bobetic potential, while the Barker-Fisher-Watts potential leads to close results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 3, pp. 62–67, March, 1979.     

The Lindemann melting parameter for argon at high pressure

Elastic constant measurements in solidified argon near the melting temperature have been made for reduced volumes corresponding to melting temperatures from 123 to 206 K. Derived values of the Debye temperature in the limit T → T_m, allowed the Lindemann parameter to be determined, showing that within experimental error, the parameter is constant along that portion of the melting line.     

A molecular dynamical study of the equation of state of solids at high temperature and pressure

The molecular dynamics method of computer simulation was used to study the pressure and energy as a function of volume and temperature for f.c.c. neon with 6–12 Lennard-Jones interatomic forces and for b.c.c. iron with Morse interatomic forces. A self-consistent cell model was used to derive analytical formulae which describe the results of the computer experiments. A method for correcting the inherently classical results of the molecular dynamics calculations for the effect of quantum statistics is proposed. The results of the calculations are compared with experimental data and with various approximate methods for calculating the Grüneisen constant.     

Prototype of an LJ solid equation of state applied to argon,krypton and methane

A prototype of an equation of state for Lennard-Jones solids is developed on the basis of modified Weeks-Chandler-Andersen perturbation theory. This prototype is found to represent the melting pressures and molar volumes of solid argon, krypton and methane.     

Supernovae and the nuclear equation of state at high densities

An extensive study of the shock-explosive mechanism for generating type II supernovae is made. The nuclear high-density equation of state plays an important role, moderate softening of the equation of state leading to a considerable increase in shock strength. A definition of shock energy which can be used throughout the life of the shock is introduced.     

A stationary filamentary microwave discharge at a high pressure of argon

A stationary discharge in the form of a filament about 1 mm in diameter is produced in a quartz tube 16 mm in diameter passed through the wider wall of a standard waveguide and field with argon at a pressure of 300 mm Hg at a microwave power of 50 W on a frequency of 7 GHz. The number of filaments increases gradually from one to seven as the power and pressure are increased. The filaments are parallel and oriented along the electric field of the wave. They are arranged symmetrically relative to the equatorial plane of the tube. The distance between the filaments decreases as their number increases. The stationary filaments arising due to ionization-overheating instability may be explained qualitatively using the interference-equilibrium model and assuming that a discharge is organized such as to provide for the maximal power absorption.     

Simulated equation of state of CaF2 with fluorite-type structure at high temperature and high pressure

The pressure-volume-temperature (P-V-T) equation of state (EOS), isothermal bulk modulus, and thermal expansivity of CaF₂ with cubic fluorite-type structure are investigated using the constant temperature and pressure shell model molecular dynamics (MD) method with effective pair potentials which consist of the Coulomb, dispersion, and repulsion interaction. It was shown that MD simulation is very successful in accurately reproducing the measured volumes of the CaF₂ over a wide range of pressures. The simulated P-V data matched X-ray diffraction experimental results up to 9.5 GPa at 300 K. In addition, volume thermal-expansion coefficient and isothermal bulk modulus were also calculated and compared with available experimental data and the latest theoretical results at ambient condition. At extended temperature and pressure ranges, The P-V EOS under different isotherms at selected temperatures, T-V EOS under different isobars at selected pressures, thermal expansivity, and isothermal bulk modulus were predicted up to 1500 K and 10 GPa. The detailed knowledge of thermodynamic behavior and EOS at extreme conditions are of fundamental importance to the understanding of the physical properties of CaF₂.     

Potentialities for solid state maser excitation by dynamic high pressure

During rapid transitions of solid state quantum systems between different high pressure equilibrium states, deviations from thermodynamical equilibrium, like in an excited maser system, are presumed.     

The first-principle study on the equation of state of HMX under high pressure

The equation of states (EOS) of high energy explosive HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) has been studied by using the first principle method. Our results include the lattice constants, elastic constants, and the dependence of total energy and pressure on volume for βand δ-HMX. The calculated elastic constants and the pressure-volume relationship of β-HMX are also compared with the experimental values. The theoretical tensile experiments are implemented on the β-HMX. The atomic-scale ana...     

First-principles calculations for structure and equation of state of MgB2 at high pressure

We investigate the structure and the equation of state of compound MgB₂ at high pressure using the full-potential linearized muffin-tin orbital scheme within the generalized gradient approximation correction in the frame of density functional theory. Through the quasi-harmonic Debye model, in which the phononic effects are considered, we have obtained successfully the bulk modulus and the thermal expansion of MgB₂.     

Strength, anisotropy, and preferred orientation of solid argon at high pressures

The elasticity and plasticity of materials at high pressure are of great importance for the fundamental insight they provide on bonding properties in dense matter and for applications ranging from geophysics to materials technology. We studied pressure-solidified argon with a boron-epoxy-beryllium composite gasket in a diamond anvil cell (DAC). Employing monochromatic synchrotron x-radiation and imaging plates in a radial diffraction geometry (Singh et al 1998 Phys.?Rev.?Lett.?80 2157; Mao et al 1998 Nature 396 741), we observed low strength in solid argon below 20?GPa, but the strength increases drastically with applied pressure, such that at 55?GPa, the shear strength exceeded 2.7?GPa. The elastic anisotropy at 55?GPa was four times higher than the extrapolated value from 30?GPa. Extensive (111) slip develops under uniaxial compression, as manifested by the preferred crystallographic orientation of (220) in the compression direction. These macroscopic properties reflect basic changes in van der Waals bondings under ultrahigh pressures.     

Diamond and cubic boron nitride under high pressure: Raman scattering,equation of state and high pressure scale

Abstract

The development of the diamond-anvil cell has stimulated Raman-scattering investigation of vibrational modes in covalent crystals. The linear pressure coefficient reported for diamond by Hanfland et at' (2.90 ± 0.05 cm-¹/GPa) agrees to within mutual experimental error with the result of Boppard et aL² (2.87±0.01 cm-¹/GPa). As to cubic boron nitride, the only work by Sanjurjo ef aL3 reports 3.45 ± 0.07 cm-¹/GPa for LO- and 3.39 ± 0.08 cm-¹/GPa for TO- modes. Since no compressibility data are availablel^1?3, the mode Griineisen parameter γ = ‐ δ In γ/δ is defined as y = K/Y·dv/aP and depends on the bulk modulus K and the calibration of the ruby scale. The above papers report y= 0.96 and y=0.95±O.O3fordiamondand γ_Lo=1.21,γTo=1.51 forBN.