Equation of state of boron carbide B 4 C

We present the results of recent experiments conducted on the Sandia Z machine and a new tabular equation of state for ${\mathrm{B}}₄\mathrm{C}$. The equation of state was calibrated to a combination of density functional calculations reported here and fits to preexisting data. It was constructed partly to recover the effects of a shock-driven, polymorphic phase transition of unknown character beginning at particle velocities of just under 3 km/s (shock pressures of 95 GPa). Some of the Z experiments included sound speeds determined by the overtaking rarefaction method, from which we calculate the Gr\"uneisen parameter and compare with previous experiments conducted at the OMEGA laser [Fratanduono et al., Phys. Rev. B 94, 184107 (2016)], our own first principles calculations, and another recent tabular equation of state [Zhang et al., Phys. Rev. E 102, 053203 (2020)]. We also compare our results with previous static compression, thermophysical, and melt studies, finding mixed consistency. We predict the onset and completion of shock melting at 225 and 265 GPa, respectively, and predict a melt curve that is largely flat to pressures of several hundred GPa.