Fig. 5: Measured diffraction peak positions and densities of SiC as a function of stress.

a The observed d-spacings of ramp-compressed SiC sample and diamond ablator/window are shown as red and gray circles, respectively. The solid lines are from static 300-K equation of state fits and their extrapolation as described below. The diamond ramp equation of state⁶⁴ and its extrapolation (>800 GPa) are shown as gray dashed curves. b Measured densities of ramp compressed SiC (red circles) and a Birch-Murnaghan (BM) equation of state fit to the reduced isentrope (red curve with assumption of Y = 20 GPa and γ₀ = 1) are compared to the extrapolated EOS of diamond anvil cell experiments (blue²⁰ and black¹⁸ curves) and the range of densities obtained from first principles calculations (orange shaded region^{20,26,27,28,29,30,31,32,33}, see Supplementary Table 3). The gray band shows the pressure-density path along the principal isentrope calculated using the thermodynamic parameters that are listed in the Suppl. Table 4. Our EOS curve is consistent with the theoretical calculations of ref. ²⁶ (purple curve). Previous shock compression data (cyan¹⁷ and green circle^15,16) and static diamond anvil cell data (open circles¹⁸) are also plotted. The datum at 433 GPa (gray parentheses) was excluded from fitting to the EOS (See Suppl. Table 2 for details). The 1σ error are shown as red bar. Gray error bars represent additional +50 GPa stress uncertainty due to uncertainty in the strength of diamond.