Metastability of diamond ramp-compressed to 2 terapascals

Abstract

Carbon is the fourth most prevalent element in the universe and essential for all known life. In the elemental form it is found in multiple allotropes including graphite, diamond, and fullerenes, and it has long been predicted that even more structures can exist at greater than Earth-core pressures. [1][2][3] . Several new phases have been predicted in the multi-terapascal (TPa) regime, important for accurately modeling interiors of carbon-rich exoplanets 4,5 . By compressing solid carbon to 2 TPa (20 million atmospheres; over 5 times the pressure at the Earth's core) using ramp-shaped laser pulses, and simultaneously measuring nanosecond-duration time resolved x-ray diffraction, we found that solid carbon retains the diamond structure far beyond its regime of predicted stability.The results confirm predictions that the strength of the tetrahedral molecular orbital bonds in diamond persists under enormous pressure, resulting in large energy barriers that hinder conversion to the more stable high-pressure allotropes 1,2 , just as graphite formation from metastable diamond is kinetically hindered at atmospheric pressure. This work nearly doubles the record high pressure at which x-ray diffraction has been recorded on any material.

Phase diagram of solid hints new fundamental constant and sees atomic orbital

“…8) under pressure up to 5 TPa (pink stars), that is superimposed upon the orbital image. The tomography confirms that even such enormous pressure cannot distort the orbitals and so the strength of their covalent bonds is enough to keep the diamond structure 23 .…”

“…Expession (2) multiplied by the four covalent bonds with this h and R=rp/4 gives the diamond melting point 4157 o C in excellent agreement with the real 4000 o C (Supplementary Table S1). To further affirm our theory, proceeding from the warrantable assumption that the diamond phase persists under enormous pressure 23 , we calculated the baric dependence of the melting-point in diamond, Ttr(P), through its (P) taken from Extended Data Table 24 1. The baric dependence of the covalent radius ] is the pressure-induced contribution resembling the energy of ideal gas U = PdV, where U = kBTtr(P) and dV=12mu[1/(0)-1/(P)] is the striction of the unit cell per a carbon, and analogous to the magnetostatic addition of Exp.…”

Development of slurry targets for high repetition-rate XFEL experiments

“…In slurry samples, lateral expansion of grains into the compressible epoxy is possible which may reduce the levels of work heating. We note that diamond-slurry samples were recently used in X-ray diffraction experiments on the National Ignition Facility for laser ramp-compression to 2 TPa, with the goal at reducing sample temperatures at these extreme levels of compression (33).…”

“…• The powder is then fully baked in a vacuum oven to remove all moisture (otherwise, in the case of diamond powder (33), the final mixture is visibly heterogeneous).…”

Molecular dynamics simulations of inelastic x-ray scattering from shocked copper

“…However, with controlled laser pulses, shaped in time, or by compressing materials via multiple shocks (which can in principle be induced by appropriate target design 69 ), the application of high pressure can be achieved in a ramped manner 57,[70][71][72][73][74] , without the compression wave steepening into a shock. This so-called 'quasi-isentropic' (QI) compression has been shown to keep material solid well into the TPa regime [75][76][77][78][79][80] .…”