# Properties of B4C in the shocked state for pressures up to 1.5 TPa

## TL;DR

This study combines density functional theory and molecular dynamics to explore the behavior of boron carbide under extreme pressures up to 1.5 TPa, revealing phase transitions, segregation, and fluid states.

## Contribution

It provides the first comprehensive analysis of B4C's properties under ultra-high pressures, including phase transitions and fluid states, using advanced computational methods.

## Key findings

- Discontinuities in the Hugoniot at 50 GPa and 90-100 GPa indicating phase changes.
- Good agreement between theoretical predictions and experimental data up to 700 GPa.
- Identification of amorphous and atomistic fluid states in B4C at high pressures.

## Abstract

Density Functional Theory calculations using the quasi-harmonic approximation have been used to calculate the solid Hugoniot of two polytypes of boron carbide up to 100 GPa. Under the assumption that segregation into the elemental phases occurs around the pressure that the B11Cp(CBC) polytype becomes thermodynamically unstable with respect to boron and carbon, two discontinuities in the Hugoniot, one at 50 GPa and one at 90-100 GPa, are predicted. The former is a result of phase segregation, and the latter a phase transition within boron. First principles molecular dynamics (FPMD) simulations were employed to calculate the liquid Hugoniot of B4C up to 1.5 TPa, and the results are compared to recent experiments carried out at the Omega Laser Facility up to 700 GPa [Phys. Rev. B 94, 184107 (2016)]. A generally good agreement between theory and experiment was observed. Analysis of the FPMD simulations provides evidence for an amorphous, but covalently bound, fluid below 438 GPa, and an atomistic fluid at higher pressures and temperatures.