Behavior of Grüneisen's parameter of some metals at high pressures

Ramakrishnan, J.; Boehler, R.; Higgins, George E.; Kennedy, George C.

doi:10.1029/jb083ib07p03535

Cited by 103 publications

(24 citation statements)

References 10 publications

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“…(e)) k = 7.31A-' as the wave vector of the This value represents an average for the inves-14.413 keV quanta. From the first moment of tigated pressure range (20 to 42 GPa) and is the DOS, we obtained a mean phonon energy slightly lower than the measured value for a-Fe E,, and, according to the Debye approxima-at ambient conditions y(a-Fe) = 1.66 (26). tion.…”

Section: Energy (Mev)mentioning

confidence: 68%

Density of Phonon States in Iron at High Pressure

Lübbers

Grünsteudel

Chumakov

et al. 2000

Science

123

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The lattice dynamics of the hexagonal close-packed (hcp) phase of iron was studied with nuclear inelastic absorption of synchrotron radiation at pressures from 20 to 42 gigapascals. A variety of thermodynamic parameters were derived from the measured density of phonon states for hcp iron, such as Debye temperatures, Gruneisen parameter, mean sound velocities, and the lattice contribution to entropy and specific heat. The results are of geophysical interest, because hcp iron is considered to be a major component of Earth's inner core.

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Section: Energy (Mev)mentioning

confidence: 68%

Density of Phonon States in Iron at High Pressure

Lübbers

Grünsteudel

Chumakov

et al. 2000

Science

123

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“…Ramakrishnan et al [1978] measured 7 for • iron (body-centered cubic) to 3.3 GPa at room temperature. Using the parameterization where subscript 0 implies values under ambient conditions, they found n = 0.6.…”

Section: Introductionmentioning

confidence: 99%

Phase transitions, Grüneisen parameter, and elasticity for shocked iron between 77 GPa and 400 GPa

Brown¹,

McQueen²

1986

J. Geophys. Res.

701

538

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Sound velocities determined in iron, shock compressed to pressures between 77 GPa and 400 GPa, indicate that two phase transitions exist on the Hugoniot. A discontinuity in sound velocities at 200 +_ 2 GPa may mark the transition of e iron to 7 iron. A second discontinuity at 243 _+ 2 GPa is believed to indicate the onset of melting. The calculated temperature at melting lies between 5000 K and 5700 K. When extrapolated from the Hugoniot melting point, the Lindemann criterion yields an estimate of 5800 +_ 500 K for the melting of pure iron at the inner core boundary pressure of 330 GPa. The product of density times the thermodynamic Grfineisen parameter in liquid iron, calculated from the present data, is 19.6 +_ 0.8 Mg m-3. A temperature profile ranging from 3800 K at the core-mantle boundary to 5000 K at the earth's center is calculated using the present data. Sound velocities for e iron provide a better match to seismic velocities for the earth's inner core than do those of 7 iron. A comparison between liquid iron velocities and the velocity profile through the outer core provides further evidence for alloying of iron with "lighter elements" in the core.

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“…However, the value of n is well determined and it appears to be significantly different from 1. Although this conclusion may vary depending on the nature of the fit and the data used,Ramakrishnan et al [1978] obtained similar results from measurements of '• at lower pressures. This would imply that the assumption often used of o'• = const [e.g., McQueen et al, 1970] is not correct for Fe at high pressures and that this assumption ,results in a smaller dependence of '• on volume than is indicated by the data.…”

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confidence: 99%

Properties of iron at high pressures and the state of the core

Jeanloz¹

1979

J. Geophys. Res.

164

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Shock-wave (Hugoniot) data for initially porous and nonporous samples of iron are inverted to yield values of the Griineisen parameter (3'), adiabatic bulk modulus (Ks), and coefficient of thermal expansion (a) along the Hugoniot to pressures of about 150 GPa (1.5 Mbar). This represents the first reliable estimate of thermal properties (e.g., a) to such high pressures based directly on experimental data. The values of 3' fit the conventional function 3' = 3,o(V/VoP but with n significantly larger than 1, while extrapolation formulas suggested to date for a appear not to provide the best fit to the data. The present analysis yields values of 3' between about 1.4 and 1.0 (essentially temperature independent)and a between about 1.0 and 0.4 X 10 -5 K -• throughout the earth's core, therefore implying that simple dynamical models of the core are quite viable. These results provide experimental confirmation of the Vaschenko-Zubarev/Irvine-Stacey (or 'free-volume') formulation for 3' of iron at high pressures, as well as support for Stacey's recent model of the thermal state of the core. The data on density, sound speed, and bulk modulus of iron are extrapolated and corrected to pressures and temperatures existing throughout the earth's core, and compared with current seismological information. This leads to the following conclusions: (1) both densities and bulk moduli in the outer core are less than those of Fe under equivalent conditions (by about 10 and 12%, respectively) but (2) their gradients through the outer core are consistent with gross chemical homogeneity (i.e., uniform intermixing of Fe and a lighter, more compressible element or compound); (3) both densities and bulk moduli for the inner core are compatible with those of iron, suggesting that (4) the inner core-outer core boundary is likely to be a compositional as well as a phase boundary. Assuming that the outer core consists of Fe and a lighter element or compound, X, the constraints on density, bulk modulus and mass fration of X which must be simultaneously satisfied are given.surements of the high-temperature, high-pressure Gri•neisen particle-velocity, u•, dependency) defining a reference Hugoparameter (3'), adiabatic bulk modulus (Ks), and coefficient of niot. Each Hugoniot state for an initially porous sample was thermal expansion (a) along the Hugoniot of iron. These can then compared for its offset (thermal pressure) at that volume then be compared with (1) the seismological properties ob-with this reference equation-of-state. The appropriate equa-

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Behavior of Grüneisen's parameter of some metals at high pressures

Cited by 103 publications

References 10 publications

Density of Phonon States in Iron at High Pressure

Density of Phonon States in Iron at High Pressure

Phase transitions, Grüneisen parameter, and elasticity for shocked iron between 77 GPa and 400 GPa

Properties of iron at high pressures and the state of the core

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