Evidence of a fcc-hcp Transition in Aluminum at Multimegabar Pressure

Akahama, Yuichi; Nishimura, M.; Kinoshita, Keisuke; Kawamura, Haruki; Ohishi, Yasuo

doi:10.1103/physrevlett.96.045505

Cited by 139 publications

(96 citation statements)

References 16 publications

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“…Comparison with experiment at 292 GPa finds agreement in the c/a ratio to within 0.1% and well within experimental uncertainty. 17 At 222 GPa the predicted value of the c/a ratio differs from experiment by 1%. Since experiments observe a region between 217 and 260 GPa in which the fcc and hcp phases coexist, this discrepancy is made more reasonable considering that the system might be out of equilibrium.…”

mentioning

confidence: 92%

“…Experiments have shown that the fcc phase may exist at pressures above the transition pressure either as a super-pressurized phase 16 or as a two phase region. 17 Therefore the mechanical properties of fcc aluminum at pressures beyond the equilibrium transition pressure, and any mechanical instabilities that may lead to mechanical failure are relevant to high pressure experiments.…”

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confidence: 99%

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Bulk aluminum at high pressure: A first-principles study

2008

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The behavior of metals at high pressure is of great importance to the fields of shock physics, geophysics, astrophysics, and nuclear materials. We study here bulk crystalline aluminum from firstprinciples at pressures up to 2500 GPa -soon within reach of laser-based experimental facilities. Our simulations use density-functional theory and density-functional perturbation theory in the localdensity and generalized-gradient approximations. Notably, the two different exchange-correlation functionals predict very similar results for the f cc → hcp, f cc → bcc, and hcp → bcc transition pressures, around 175 GPa, 275 GPa, and 380 GPa respectively. In addition, our results indicate that core overlaps become noticeable only beyond pressures of 1200 GPa. From the phonon dispersions of the fcc phase at increasing pressure, we predict a softening of the lowest transverse acoustic vibrational mode along the [110] direction, which corresponds to a Born instability of the fcc phase around 725 GPa.First-principles calculations have proved useful to the fields of geophysics, 1 astrophysics, 2 and nuclear materials. 3 Aluminum, being cubic close-packed and having no d-shell electrons, is a prototype for theoretical predictions and understanding the high-pressure behavior of simple metals. 4 Currently the National Ignition Facility 5 at LLNL is expected to achieve shockless compression 6 of metals up to 2000 GPa. This new facility may provide rapid advancements to high-pressure physics and could partner very successfully with theoretical studies.The equation of state (EOS) and phase stability of aluminum were first studied from first-principles in the early 1980s. 7,8,9 In all cases the predicted phase sequence was f cc → hcp → bcc, but predictions differed greatly in the transition pressures. Several other calculations within the local-density approximation (LDA) 10 or the generalized-gradient approximation (GGA) 11,12 have since then been performed, with a predicted static (i.e. without the phonon contribution) f cc → hcp transition pressure of 205 ± 20 GPa 10 in LDA and 170 GPa 11 and 192 GPa 12 in GGA. These discrepancies are more notable for the hcp → bcc transition pressure: 565 ± 60 GPa 10 in LDA versus 360 GPa 11 in GGA, leaving significant uncertainties open. Theoretical work on the vibrational properties of aluminum also suggests for the f cc → hcp transition a transition pressure higher than the static one. 11,12 Elastic properties 13,14 and the absolute strength under tension 15 have also been calculated; the latter results are of particular interest as they demonstrate the important role vibrational modes play in determining mechanical stability and suggest that shear failure modes are inherent in aluminum.Experimentally, the equation of state of aluminum at high pressures was studied by shock-compression 16 at pressures above the predicted maximum for the f cc → hcp phase boundary, 10 but a transition was not observed. However recent diamond anvil cell experiments observed a f cc → hcp transition at 217 ± 10 GPa 17 ...

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confidence: 99%

Bulk aluminum at high pressure: A first-principles study

2008

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“…2(b). Akahama et al 24) recently studied the high pressure structure of Al up to 333 GPa by powder Xray diffraction at 297 K. They confirmed that there was no phase transition below 100 GPa, i.e., the fcc structure is stable up to this pressure. References from Hänström et al, 5) Dewaele et al, 6) Boehler et al, 25) and Syassen et al 26) are also included in this assessment.…”

Section: Aluminummentioning

confidence: 73%

Assessment of Temperature and Pressure Dependence of Molar Volume and Phase Diagrams of Binary Al–Si Systems

Liu

Oikawa

2014

Mater. Trans.

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This article reports the thermodynamic assessment of the temperature and pressure dependence of the molar volume of AlSi binary systems, as well as PT unary and high pressure binary phase diagrams based on the CALPHAD methodology. The molar volumes of stable fcc Al, diamondSi, and liquid phases as a function of temperature were directly assessed from the data reported in the literature whereas that of metastable fccSi was determined by extrapolating composition dependent volume data for AlSi and CuSi fcc solid solutions through extrapolation to pure Si at atmospheric pressure. The Brosh equation of state, which incorporates the quasi-harmonic model, was implemented to avoid spurious estimations of negative heat capacity and thermal expansion at high pressure; it was subsequently used to predict the corresponding values for these properties. Additionally, the temperature and composition dependence of the molar volume as well as phase diagrams for the binary system at high pressure were calculated. Good agreement was reached between calculated results and experimentally estimated thermodynamic values.

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“…The shaded region corresponds to the P-T space for Al in the solid state. [Asay, 1997] The fcc-to-hcp and hcp-to-bcc transitions are based on the predictions and observations described in [Akahama, 2006;Boettger, 1996;Moriarty, 1995]. This 300 µm wide vacuum gap allows the reservoir material to expand as it propagates across to the sample, resulting in a soft and continuous pressure rise in the sample.…”

Section: Figure Captionsmentioning

confidence: 99%

“…1 for aluminum. [Asay, 1997;Akahama, 2006;Moriarty, 1995;Boettger, 1996] We show in Fig. 1 an illustrative P-T phase diagram for Al, [Young, 1991; along the principle Hugoniot.…”

Section: Introductionmentioning

confidence: 99%

High pressure, quasi-isentropic compression experiments on the Omega laser

Lorenz

Edwards

Jankowski

et al. 2006

High Energy Density Physics

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Abstract:The high energy density of pulsed lasers can be used to generate shockless loading in solids to high pressures and compressions but low temperatures. [Edwards, 2004] We have used the Omega laser to extend the capabilities of this technique to multiMbar pressures and compressions approaching a factor of 2 in aluminum foils. The energy from a 3.7 ns laser pulse is used to drive a strong shock through a 200 µm polystyrene disc. The disc material unloads from a high-pressure state and expands across a 300 µm vacuum gap where it stagnates against the sample to produce a smooth, monotonically increasing load with rise times from a few to ~20 ns. Ramped compression waves having peak pressures of 14-200 GPa (0.14-2.0 Mbar) and peak compressions ρ/ρ 0 of 1.1-2.0 were generated in the aluminum samples using laser pulse energies of 400 J to 2 kJ. Wave profiles from a series of successively thicker targets loaded to 120 GPa show the evolution of the high-pressure compression wave within the sample. The initial loading in the sample is shockless, and develops into a shock at a depth of 20-25 µm. We compare these wave profiles with hydrodynamic simulations from which we extract material temperatures and plastic strain rates behind the compression wave. Limitations and future prospects for this new shockless loading technique are discussed.2

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Evidence of a fcc-hcp Transition in Aluminum at Multimegabar Pressure

Cited by 139 publications

References 16 publications

Bulk aluminum at high pressure: A first-principles study

Bulk aluminum at high pressure: A first-principles study

Assessment of Temperature and Pressure Dependence of Molar Volume and Phase Diagrams of Binary Al–Si Systems

High pressure, quasi-isentropic compression experiments on the Omega laser

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Evidence of a fcc-hcp Transition in Aluminum at Multimegabar Pressure

Cited by 139 publications

References 16 publications

Bulk aluminum at high pressure: A first-principles study

Bulk aluminum at high pressure: A first-principles study

Assessment of Temperature and Pressure Dependence of Molar Volume and Phase Diagrams of Binary Al&ndash;Si Systems

High pressure, quasi-isentropic compression experiments on the Omega laser

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Assessment of Temperature and Pressure Dependence of Molar Volume and Phase Diagrams of Binary Al–Si Systems