Shock-Wave Exploration of the High-Pressure Phases of Carbon

Abstract

it is furthermore crucial to note that a distinct part of the nucleation driving force given by the change in Gibbs energy is already released by stable cluster formation (SOM section 2.6, fig. S14, and Fig. 2).Prenucleation-stage cluster formation on the basis of equilibrium thermodynamics can be qualitatively shown also for the biominerals calcium phosphate and calcium oxalate (SOM section 2.7 and fig. S15) and suggests a similar nucleation mechanism for these minerals. The clusterformation mechanism on the basis of equilibrium thermodynamics can be speculatively explained by entropic solvent effects. The probable release of water molecules from the hydration layer of ions caused by cluster formation may result in an increased number of degrees of freedom of the system. In classical nucleation theories, only enthalpic effects (interaction potentials) are taken into account, and entropic solvent effects are neglected. In the end, a pH-dependent change of ionic hydration layers may explain the pH dependency of cluster-formation thermodynamics. The high-energy density behavior of carbon, particularly in the vicinity of the melt boundary, is of broad scientific interest and of particular interest to those studying planetary astrophysics and inertial confinement fusion. Previous experimental data in the several hundred gigapascal pressure range, particularly near the melt boundary, have only been able to provide data with accuracy capable of qualitative comparison with theory. Here we present shock-wave experiments on carbon (using a magnetically driven flyer-plate technique with an order of magnitude improvement in accuracy) that enable quantitative comparison with theory. This work provides evidence for the existence of a diamond-bc8-liquid triple point on the melt boundary.

Multiphase equation of state for carbon addressing high pressures and temperatures

“…14). Also shown on this figure are data from static compression measurements of the room-temperature isotherm [82] (green circles at the lowest P ), magnetically driven flyer plate studies [8] (dense set of magenta + symbols with ρ ∼ 6-7 g/cc), and multiple sets of laser-shock data on the principal Hugoniot of diamond (symbols with error bars) [1][2][3][4][5]. Note that much of the highest-P Hugoniot data [1] seems to straddle the 300 K isotherm, even well above P = 1000 GPa; indeed, the data of Brygoo et al [4] even fall below our prediction of the room-T isotherm.…”

“…Recent laser-shock and ramp-compression studies [1][2][3][4][5][6][7], together with shock measurements performed with magnetically driven flyer plates [8], have produced data in the range from P = 0-50 Mbar. In addition, theoretical work on the EOS and phase diagram in this same range has yielded predictions which are largely (though not completely) in accord with these experimental data [8,9]. These studies were conducted with density functional theory (DFT) molecular dynamics (MD).…”

Computational prediction of body-centered cubic carbon in an all-sp3six-member ring configuration

“…22 Moreover, a body-centered cubic carbon denoted BC8 is suggested to be the highpressure modification of carbon derived from cubic diamond under pressure of ∼ 1100 GPa. [23][24][25] Among all these carbon structures, only BC8 carbon comprises entirely a diamond-like six-membered-ring bonding structure, while other reported sp 3 hybridized carbon structures contain mixed bonding configurations, such as the (5+6+7)-membered-ring in M carbon, 10 (4+6+8)-membered-ring in Z carbon, 13 or (3+6+7)-memberedring in SC24 carbon. 22 In this paper, we report by ab initio calculations a body-centered cubic carbon phase with a 24-atom unit cell in Ia3d symmetry with all-sp 3 six-membered rings, which is the same bonding type as cubic diamond (8-atom unit cell in F d3m symmetry) and BC8 carbon (16-atom unit cell in Ia3 symmetry).…”

Controlled incorporation of mid-to-high Z transition metals in CVD diamond

“…We also grew single crystalline metal-doped diamond films by using single crystalline natural diamond substrates with (111), (110), and (100) orientations, and their single crystalline character was verified by electron backscatter diffraction (EBSD). The metal precursors (Mo(CO) 6 and W(CO) 6 ) were delivered from a thermally stabilized source using H 2 as a carrier gas, and the precursor mole fraction in the plasma chamber was controlled by regulating the flow rate of the carrier gas (0-150 sccm) as well as the source temperature (298-318 K). The saturation vapor pressure of Mo(CO) 6 [25; 26] (W(CO) 6 [27]) in the source increases from 0.2 (0.03) mbar at 298 K to 1.4 (0.2) mbar at 318 K. For sample characterization, freestanding diamond wafers were prepared by removing the Si substrate using a hot KOH etch solution.…”

“…Recently, diamond and its defect centers have received much interest in the fields of solid-state quantum computing [1][2][3], nanoscale magnetic sensor applications [4], and inertial confinement fusion where diamond is emerging as a promising ablator material [5][6][7]. In the latter application, the controlled incorporation of transition metals in diamond offers an opportunity to tailor diamond's x-ray adsorption properties to reduce preheating of the deuterium-tritium fuel and limit the growth of hydrodynamic instabilities [8].…”