Carbon equation of state at high pressure: the role of the radiative transport in the impedance mismatch diagnostics

The EOS of carbon at high pressure is a subject of interest for several branches of physics, including astrophysics (a correct description of high-pressure phases is essential for realistic models of planets and stars [13, 22], in particular for the explanation of large magnetic fields of giant planets such as Uranus and Neptune [19, 20]), material science (carbon is a unique element due to its polymorphism and complexity, and a large variety of different phase states), and applied engineering (for example the inertial confinement fusion research). The important phenomenon of carbon metallization at high pressure had been predicted theoretically, but a convincing experimental demonstration of this effect is still lacking. According to first theoretical estimates [24] the triple point for the transition among diamond, liquid metal, and solid metal should occur at 1.7 Mbar and 3100 K, but this prediction was contradicted by the experiments [11, 23]. More recent works predict a much higher pressure for the metallic transition. At higher temperatures, the presence of liquid phases was predicted, going from non-metallic at low pressure to semi-metallic and metallic at high pressure. The first experimental evidence of a liquid metallic phase was presented in [6, 7]. Nowadays, the most accepted phase diagram of carbon by Grumbach and Martin [12] sets the structural changes in liquid carbon from approximately fourfold to approximately sixfold coordination (metallic liquid) in the pressure range of 4–10 Mbar. This liquid metallic phase may be generated in laboratory conditions using laser-driven shocks. Indeed, the laser-induced ablation and plasma expansion into vacuum result in a material being pushed in the opposite direction, thus generating a shock wave. The Carbon equation of state at high pressure: the role of the radiative transport in the impedance mismatch diagnostics Abutrab A. Aliverdiev, Dimitri Batani, Riccardo Dezulian, Tomasso Vinci