High-pressure Equation Of State Research Articles

High-Pressure Equation of State for Solids and Solution of the Riemann Problem

Equation for the state surface for solids in terms of the specific internal energy, entropy and specific volume has been discussed in detail starting from the Gruneisen assumption. It has been revealed that the Gruneisen assumption leads us to the specific heat at constant volume to be the function of entropy only. Riemann integral written in the generalized form independent of the assumption on the Gruneisen γ has been obtained, and the strategy to reach the solution of the Riemann problem has been shown.

Equations of state and optical properties of the high pressure phase of zinc sulfide

The static compression of the high pressure (B1) phase of zinc sulfide has been measured at room temperature using X-ray diffraction through a diamond anvil cell between 11 and 45 GPa. The volume, the bulk modulus, and its derivative of the B1 phase, extrapolated to zero pressure, are V 02 V 01 = 0.851 (±0.021), K 02 = 85.0 (±3.8) GPa , and K' 02  4 based on a third order Birch-Murnaghan finite strain analysis. Alternatively, a universal equation of state fit yields V 02 V 01 = 0.895 , K 02 = 47.5 (±8.2) GPa, and K 02 = 6.2 (±1.1). The large discrepancy between these two sets of zero pressure parameters highlights the difficulty in extrapolating properties from a high pressure equation of state. Thin samples of the high pressure phase of zinc sulfide were discovered to transmit light in the visible region. Optical absorption spectra were recorded from 15.9 to 36.2 GPa. With the increase of a few GPa in pressure past the phase transition at 15 GPa, the direct band gap narrows to approximately 2.1 eV. Further compression induces a slight, but poorly resolved, increase of direct gap energy with compression ( ≈ 10 meV GPa ).

Iow-teperature lattice properties of transtticn metals : pseudopotential model coupled with band structure calculation

Recently we have shown that pseudcpotential (PP) model is applicable in the study of lattice statics, dynamics, and thermodynamics of transition metals. Here this model is smnarized and new results are given obtained e.g.for metastable FCC phases of Co and Fe, for high pressure equation of state (DOS) of Cu. For the first time our model is used in the study of disordered alloys.

High-pressure equation of state for solid krypton from interatomic potentials

The pressure-volume isotherm for krypton at 300 K is evaluated by the Monte Carlo method using pair and three-body potentials. The pair potentials used are that of Aziz and Slaman and a slightly modified version of their potential which gives better agreement with high-energy scattering data. The three-body potentials considered are the Axilrod-Teller interaction and the first-order three-body exchange interaction as parametrized by Loubeyre. The results are compared with recent measurements at pressures up to 300 kbar and the implications of the comparison are discussed. The best agreement with experiment is found using the Axilrod-Teller interaction as the only many-body interaction, indicating that the three-body exchange interaction is to a large extent canceled by higher many-body interactions, at least in the highly symmetrical environment of the crystal.

High pressure equation of state for solid xenon from interatomic potentials

The interatomic pair potential for xenon recently derived by Aziz and Slaman (AS) is used to calculate pressure as function of volume for solid xenon, and the results are compared with experimental data and with those calculated using the earlier potential of Barker, Klein and Bobetic (BKB). If the Axilrod-Teller (AT) interaction is included agreement with experiment is good up to 50 kbar for either potential but there are deviations at higher pressures, larger for the earlier potential. A pair potential which gives better agreement with high pressure solid state data at the expense of worse agreement with gas viscosities is described, and the respective roles of many-body interactions and uncertainties in the pair potential in explaining the discrepancies with experimental solid-state pressures are discussed. Published electronic calculations are shown to give remarkably good agreement with the high-pressure experimental data.

High pressure equation of state for solid argon from interatomic potentials

The pressure–volume isotherm for solid argon at 298 K is calculated by the Monte Carlo method using the pair potential of Barker, Fisher, and Watts (BFW) together with the Axilrod–Teller (AT) three-body interaction. Comparison is made with recent experimental data of Ross and co-workers extending up to 800 kbar. Agreement with experiment is good though not perfect. Comparison is made with the pair potentials of Aziz and Chen and Koide, Meath, and Allnatt and with the exp-6 ‘‘effective’’ pair potential of Ross.

Helium at high density

We show that all available high pressure equation of state and melting data for helium can be fitted with an exponential-six potential. This potential is slightly softer than the best theoretical pair potentials and thus implies the existence of attractive many- body forces. The theory also predicts a zero Kelvin fcc to bcc phase transition at 10.6 Mbar, and a maximum temperature of 690 K for the fcc phase.

Structural Phase Transformamtion and the Equation of State of CsCI, CsBr, and CsI Crystals

AbstractThe structural phase transformation of CsCl crystals under the effect of high temperature is investigated using an interionic potential model which takes account of repulsive interactions up to second neighbours and of van der Waals (vdW) interactions between dipole‐dipole and dipole‐ quadrupole. It is found that the transition temperature at which the CsCl crystal transforms from B2 (CsCI) to B1 (NaCl) structure can be predicted correctly only if larger values of vdW potentials are used in calculations. The same potential parameters are used to predict the high pressure equation of state for CsCl, CsBr, and CsI crystals. The use of overlap integrals in the Born‐Mayer potential form yields good agreement between theory and experiment for the high pressure compression data.

Total energy and pressure in the Gaussian-orbitals technique. I. Methodology with application to the high-pressure equation of state of neon

Callaway, Zou, and Bagayoko [Phys. Rev. B 27, 631 (1983)] (CZB) have presented algorithms for extracting crystalline total energies from Fourier-transform, linear combinations of Gaussian-type orbitals (LCGTO's), local-density-functional electronic-structure calculations. To obtain stable total energies as well as direct (i.e., virial theorem) pressures for a wide variety of systems, the CZB algorithms must be modified to remove unphysical numerical instabilities, achieve crucial cancellations, etc. Excellent results are obtained for bcc Li with these techniques and an appropriately enriched basis. Equation-of-state studies on a prototype molecular crystal, fcc Ne, reveal difficulties related to the Fourier-transform techniques. The most important is the approximate treatment (the linear term in a density shift expansion) of the iterative improvement of the exchange-correlation-potential Fourier coefficients. These difficulties are completely controlled and the density expansion is rendered rapidly convergent by use of an improved version of the augmented-plane-wave to LCGTO conversion technique previously reported. That procedure is used to predict the fcc Ne equation of state to 2.8 Mbar as an extension of the 0-150-kbar experimental data. The calculated high-pressure electronic structure also yields a secondary prediction: There is no metallization in the fcc phase through 2.8 Mbar.

The high-pressure equation of state of solid molecular tritium

We have calculated the equation of state for solid molecular tritium using a semiempirical approach, closely guided by experimental results for H2 and D2. TheT=0 K isotherm is calculated from a self-consistent phonon model of the free energy. Temperature effects are treated by the Mie-Gruneisen model. A tabulation of pressure, bulk modulus, and thermal expansion is given for a dense set of molar volumes, as a function of temperature up toP=22 kbar.

High pressure equation of state of rubidium

The pressure-volume relation of rubidium metal is studied by high-pressure x-ray diffraction up to 110 kbar at room temperature. In addition, pressure scans of the near-infrared reflectivity are recorded up to 250 kbar. Rubidium undergoes a bcc to fcc structural transition (Rb I → Rb II) at 70 ± 2 kbar. Other phase transitions occur at 128 ± 3, 160 ± 5 and 190 ± 5 kbar on the ruby pressure scale. The pressure-volume relation and the near-infrared reflectivity provide evidence for a pressure-induced 5s → 4d electronic transition similar to the well-known 6s → 5d transition in cesium metal.

Test of a high pressure equation of state

Spectroscopic measurements of the spectral lines in MnF2 and RbMnF3 have been carried out in the temperature range 10–300 K. Observations of exciton–magnon sidebands in the fine structures of the 6A1g → 4T2g (4D) state of Mn2+ ions are reported at low temperatures. The temperature dependence of peak positions, oscillator strength and half line widths have been investigated for selected bands. The analysis of the temperature dependence of these parameters confirms that the fine structure of the D band is mainly attributed to spin–orbit interaction combined with spin multiplicity in the ordered state. The ratios for the separation energies between these lines are fitted with the ratios expected from Landé interval rule.

A new high pressure equation of state for seawater

(1982). A new high pressure equation of state for seawater. Marine Geodesy: Vol. 5, No. 4, pp. 367-370.

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.

A new high pressure equation of state for seawater

A new high pressure equation of state for water and seawater has been derived from the experimental results of Millero and coworkers in Miami and Bradshaw and Schleicher in Woods Hole. The form of the equation of state is a second degree secant bulk modulus K = Pv 0 (v 0−v p =K 0+AP+BP 2 K = K w 0+aS+bS 3 2 A = A w+cS+dS 3 2 B = B w+eS where ν 0 and ν P are the specific volume at 0 and P applied pressure and S is the salinity (ℵ). The coefficients K W O , A W , and B W for the pure water part of the equation are polynomial functions of temperature. The standard error of the pure water equation of state is 4.3 × 10 −6 cm 3 g −1 in ν W P . The temperature dependent parameters a, b, c, d, and e have been determined from the high pressure measurements on seawater. The overall standard error of the seawater equation of state is 9.0 × 10 −6 cm 3 g −1 in ν P . Over the oceanic ranges of temperature, pressure, and salinity the standard error is 5.0 × 10 −6 cm 3 g −1 in ν P . This new high pressure equation of state has recently (1979) been recommended by the UNESCO Joint Panel on Oceanographic Tables and Standards for use by the oceanographic community.

High pressure equation of state and sound velocities to fourth order elastic constants. Application to sodium chloride to 270 kbars

Using the theory of small deformation superposed on a finite strain, we expand the strain energy to fourth order in terms of the strain invariants, and derive an athernal expression for the equation of state and the longitudinal and shear velocities of sound of a homogeneous Isotropic material to fourth order elastic constants. We evaluate reported velocity data in sodium chloride by Voronov and Grigorev to 80 kbar in terms of our formulation, to predict the equation of state to 270 kbar. Experiments performed in our laboratory (Frankel, Rich, and Homan) to 270 kbar which use ultrasonic interferometry to obtain resonance frequency intervals in the specimen were also evaluated. Both results are in good agreement with Decker's equation of state.