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We explore the structural evolution of highly oriented pyrolytic graphite (HOPG) under detonation-induced shock conditions using in − situ synchrotron X-ray diffraction in the ns time scale. We observe the formation of hexagonal diamond (lonsdaleite) at pressures above 50 GPa, in qualitative agreement with recent gas gun experiments. First-principles density functional calculations reveal that under uniaxial compression the energy barrier for the transition towards hexagonal diamond is lower than cubic diamond. Finally, no indication of cubic diamond formation was observed up to >70 GPa.

We present laser-driven shock Hugoniot measurements of single-crystal (SC) 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) between 15 and 83 GPa, spanning pressures below and well above the Chapman–Jouguet pressure of ∼28 GPa for TATB formulations (TATB grains mixed with plastic binders at 5–10 wt. %). The new SC data are generally ∼3% more compressible than previously published data on neat and formulated TATB measured in gas-gun and explosive-driven experiments. An exception is at compressions in the density of ∼1.5 (∼30–40 GPa), where our new SC data exhibit significantly lower pressures than previous results on overdriven TATB formulations, suggesting that our SC samples remain largely unreacted below 35 GPa over the short nanosecond-time scales inherent to our laser-driven experiments. These novel equation-of-state measurements are a critical step toward understanding TATB in its most fundamental form and improving predictive modeling of TATB-based explosives.

We present measurements of diamond formation in doubly shocked Stycast 1266 epoxy (comprising C, H, Cl, N, and O) using in situ x-ray diffraction. Epoxy samples were reshocked against a LiF window to pressures between 80 and 148 GPa in experiments at the Omega Laser Facility. The pressure and temperature conditions were diagnosed in situ using velocimetry and optical pyrometry, respectively. X-ray diffraction patterns of the compressed epoxy are consistent with cubic diamond (Fd[Formula: see text]m), indicating that diamond can precipitate not only from twice-shocked CH polystyrene [Kraus et al. Nat. Astron. 1, 606 (2017)] at these conditions but also from twice-shocked CH polymers with the addition of oxygen, nitrogen, and chlorine. These results, in combination with previous works on CH, [Formula: see text], [Formula: see text], and methane hydrate, support that diamond often, but not always, forms from CH-based compounds at extreme pressures and temperatures, indicating that the chemical composition, thermodynamic compression path, and kinetics play an important role.

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