Properties of diamond under hydrostatic pressures up to 140 GPa

Abstract

Diamond is the archetypal covalent material. Each atom in an sp(3) configuration is bonded to four nearest neighbours. Because of its remarkable properties, diamond has been extensively studied. And yet our knowledge of the properties of diamond under very high pressure is still incomplete. Although diamond is known to be the preferred allotrope of carbon at high pressure, the possibility of producing under pressure high-density polymorphs of diamond, including metallic forms, has been discussed. Structural changes have already been reported in diamond under non-hydrostatic pressures around 150 GPa and large deformation. However, measurements of the properties of diamond under hydrostatic pressure have been limited to below 40 GPa. Here, we report accurate measurements of the volume and of the optical phonon frequency of diamond under hydrostatic pressure up to 140 GPa. We show that diamond is more compressible than currently expected. By combining the volume and the frequency pressure shifts, we deduce that diamond remains very stable under pressure: it is a Gruneisen solid up to at least 140 GPa, and the covalent bond is even slightly strengthened under pressure. Finally, the optical phonon frequency versus pressure is calibrated here to be used as a pressure gauge for diamond anvil cell studies in the multi-megabar range.

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

“…The band structure and density of states are calculated using the hybrid functionals (HSE06). 30 The calculated band gap for diamond is about 5.43 eV, which is closed to the experimental data of 5.47 eV, 35 suggesting the validity of HSE06 method in predicting band gaps for diamond and related sp 3 bonded carbon structures. For BC12 carbon, as shown in Fig.…”

“…I: Calculated equilibrium structural parameters (space group, lattice parameter a, volume per atom V0, density ρ, bond lengths dC−C , bond angles ∠C-C-C), total energy per atom Etot, electronic band gap Eg, and bulk modulus B0 for diamond, BC8, BC12, and SC24 carbon at zero pressure, compared to available experimental data. 20,35 Structure Space group Method a (Å) …”

“…34 The calculated equilibrium structural parameters and bulk modulus for diamond, BC8, BC12, and SC24 carbon at zero pressure are summarized in Table I, compared to available experimental data. 20,35 As listed in Table I, our calculated lattice parameter is 5.116 Å from LDA and 5.172 Å from GGA. Considering LDA tends to underestimate and GGA tends to overestimate the lattice parameter, the actual value should be somewhere in between, which very well matches the experimental value of 5.14 Å found in the shock-compressed tetracyanoethylene (TCE) powder.…”

Experimental method for in situ determination of material textures at simultaneous high pressure and high temperature by means of radial diffraction in the diamond anvil cell

“…Spectroscopic methods have been used to determine the accurate pressure using fluorescence shifts in ruby, SrB 4 O 7 :Sm 2+ or yttrium aluminum garnet crystals. [18][19][20] More recently shifts in the first order Raman peaks of diamond 34 and cubic boron nitride 20 at high temperature have also been used. Alternatively, one may determine pressure using a P-V-T thermal equation of state ͑EoS͒ of an internal standard such as Au or Pt.…”

“…44 Textures obtained in hcp iron seem different from those reported before. 5, 16,34 Further study and modeling will be re- quired for full interpretation, which goes beyond the scope of this paper.…”