Diamond at 800 GPa (original) (raw)
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Nano-Diamond compressibility at pressures up to 85 GPa
2006
The pressure-volume relationship of nano-size diamond was studied at pressures up to 85 GPa. In-situ, monochromatic x-ray experiments, were performed in a diamond-anvil-cell, in a medium that provided pseudohydrostatic pressure conditions. Individual peaks were fitted using the Birch-Murnaghan equation-of-state, providing different compressibilities for the surface layer (expanded structure with longer interatomic distances) and the core of the nano-size diamond particles.
Equation of state and strength of diamond in high-pressure ramp loading
Physical Review B, 2022
Diamond is used extensively as a component in high energy density experiments, but existing equation of state (EOS) models do not capture its observed response to dynamic loading. In particular, in contrast with first principles theoretical EOS models, no solid-solid phase changes have been detected, and no general-purpose EOS models match the measured ambient isotherm. We have performed density functional theory (DFT) calculations of the diamond phase to ∼10 TPa, well beyond its predicted range of thermodynamic stability, and used these results as the basis of a Mie-Grüneisen EOS. We also performed DFT calculations of the elastic moduli, and calibrated an algebraic elasticity model for use in simulations. We then estimated the flow stress of diamond by comparison with the stress-density relation measured experimentally in ramp-loading experiments. The resulting constitutive model allows us to place a constraint on the Taylor-Quinney factor (the fraction of plastic work converted to heat) from the observation that diamond does not melt on ramp compression.
American Mineralogist
The volume bulk modulus, together with its temperature dependence, and the thermal expansion of 13 diamond at various pressures, were calculated from first principles in the [0, 30GPa] and [0, 3000K] 14 pressure and temperature ranges. The hybrid HF/DFT functional employed (WC1LYP) proved to be 15 particularly effective in providing a very close agreement between the calculated and the available 16 experimental data. In particular, the bulk modulus at 300K was estimated to be 444.6 GPa (K' = 3.60); 17 at the same temperature, the (volume) thermal expansion coefficient was 3.19·10 -6 K -1 . To the 18 authors' knowledge, among the theoretical papers devoted to the subject, the present one provides 19 the most accurate thermo-elastic data in high pressure and temperature ranges. Such data can 20 confidently be used in the determination of the pressure of formation using the "elastic method" for 21 minerals found as inclusions in diamonds, thus shading light upon the genesis of diamonds in the 22 Earth's upper mantle. 23 keywords: diamond, thermo-elastic properties, thermal expansion, ab initio calculations. 24 25 35 Earth's mantle) at which the inclusions were formed (Nestola et al. 2011; Izraeli et al. 1999) using the 36 so called "elastic method" (see Shirey et al. 2013 for a review). However, to this end, very accurate 37 data concerning the pressure-volume equation of state, the thermal expansion and the bulk modulus 38 temperature dependence of both diamond and its inclusions are absolutely crucial in order to obtain 39 low error in the pressure of formation. 40 As concerns diamond, previous experimental and theoretical determinations of the elastic parameters 41 and thermal expansion existed. In particular, from the experimental side, the elastic constants 42 measurements from Brillouin scattering, at room or higher temperatures, allowed the estimation of 43
Possible high-pressure phase of diamond
Physical Review B, 1998
We theoretically investigate a hypothetical sp 3 form of diamond carbon with 16 atoms per unit cell. It contains fivefold rings as a possible result of fullerene transformation under pressure and could be a stable phase of diamond at high pressure. We have calculated the ground-state structure, the cohesive energy, the bulk modulus, and the electronic density of states by means of tight-binding molecular-dynamics and densityfunctional total-energy calculations. Finally we have compared the phonon spectra at ⌫ and the Raman spectra to existing Raman data for a possible noncubic phase of diamond. ͓S0163-1829͑98͒02109-2͔
Testing diamond strength at high pressure
Diamond and Related Materials, 2011
We present two designs to measure the strength of diamond, natural or synthetic, above 30 Mbar. Both designs are based on the Rayleigh-Taylor instability carried out on a laser system providing a truncated ignition pulse. The first is an indentation technique which can be challenging to diagnose because of the low-Z value of carbon. The second is similar to that used in DAC (diamond anvil cell) experiments with a flat diamond squeezing a highly perturbed gold foil and provides the required high-Z diagnostics. Based on two-dimensional hydrocode simulations we conclude that the second technique is superior because of its sensitivity to diamond strength coupled with the benefit of diagnostics at these extremely high pressures.
Melting temperature of diamond at ultrahigh pressure
Nature Physics, 2009
Since Ross proposed that there might be 'diamonds in the sky' in 1981 (ref. 1), the idea of significant quantities of pure carbon existing in giant planets such as Uranus and Neptune has gained both experimental 2 and theoretical 3 support. It is now accepted that the high-pressure, high-temperature behaviour of carbon is essential to predicting the evolution and structure of such planets 4 . Still, one of the most defining of thermal properties for diamond, the melting temperature, has never been directly measured. This is perhaps understandable, given that diamond is thermodynamically unstable, converting to graphite before melting at ambient pressure, and tightly bonded, being the strongest bulk material known 5,6 . Shockcompression experiments on diamond reported here reveal the melting temperature of carbon at pressures of 0.6-1.1 TPa (6-11 Mbar), and show that crystalline diamond can be stable deep inside giant planets such as Uranus and Neptune 1-4,7 . The data indicate that diamond melts to a denser, metallic fluid-with the melting curve showing a negative Clapeyron slope-between 0.60 and 1.05 TPa, in good agreement with predictions of first-principles calculations 8 . Temperature data at still higher pressures suggest diamond melts to a complex fluid state, which dissociates at shock pressures between 1.1 and 2.5 TPa (11-25 Mbar) as the temperatures increase above 50,000 K.
High-pressure thermal expansion, bulk modulus, and phonon structure of diamond
Physical Review B, 1999
The thermodynamic properties of diamond at high pressures ͑up to 1000 GPa͒ have been investigated using the ab initio pseudopotential plane wave method and the density-functional perturbation theory. The P-V-T equation of states has been calculated from the Helmholtz free energy of the crystal in the quasiharmonic approximation. The pressure dependence of the equilibrium lattice constant, bulk modulus, mode Grüneisen parameters, and phonon structures has been presented. Some interesting dynamical features of diamond have been found at high pressures: ͑a͒ The thermal expansion coefficient decreases with the increase of pressure. At ultrahigh pressure (у700 GPa), diamond exhibits a negative thermal expansion coefficient at low temperatures. ͑b͒ The phonon frequency at X 4 and L 3 Ј gradually goes higher than that of X 1 and L 2 Ј , respectively. ͑c͒ The unusual overbending of the uppermost phonon dispersion curves near ⌫ 25 Ј decreases with the increase of pressure. Such overbending results in a maximum in the phonon density of states, which has been invoked in the previous study ͓Phys. Rev. B 48, 3164 ͑1993͔͒ to explain the famous sharp peak in the two-phonon Raman spectrum of diamond. Our present results predict that this sharp peak near the high-frequency cutoff will decrease with the pressure. ͓S0163-1829͑99͒03137-9͔ PHYSICAL REVIEW B 1 OCTOBER 1999-I VOLUME 60, NUMBER 13 PRB 60 0163-1829/99/60͑13͒/9444͑6͒/$15.00 9444
Computational Materials Science
It is been widely experimentally reported that Si under static compression (typically in a Diamond Anvil Setup-DAC) undergoes different phase transitions. Even though numerous interatomic potentials are used for numerical studies of Si under different loading conditions, the efficacy of different available interatomic potentials in determining the phase transition behavior in a simulation environment similar to that of DAC has not been probed in literature which this manuscript addresses. Hydrostatic compression of Silicon using seven different interatomic potentials demonstrates that Tersoff(T0) performed better as compared to other potentials with regards to demonstration of phase transition. Using this Tersoff(T0) interatomic potential, molecular dynamics simulation of cubic diamond single crystal silicon has been carried out along different directions under uniaxial stress condition to determine anisotropy of the samples, if any.-tin phase could be observed for the [0 0 1] direction loading whereas Imma along with-tin phase could be observed for [0 1 1] and [1 1 1] direction loading. Amorphization is also observed for [0 1 1] direction. The results obtained in the study are based on rigorous X-ray diffraction analysis. No strain rate effects could be observed for the uniaxial loading conditions.