Phase transformation in boron under shock compression

Abstract

Boron HugoniotPressure (GPa) Density (g/cm 3 ) Marsh,1980 Le Pape,2013 α-B12 β-B106 γ-B28 α-Ga liq.(γ-B28) liq.(α-Ga) Using first-principles molecular dynamics, we calculated the equation of state and shock Hugoniot of various boron phases. We find a large mismatch between Hugoniots based on existing knowledge of the equilibrium phase diagram and those measured by shock experiments, which could be reconciled if the α-B 12 /β → γ-B 28 transition is significantly over-pressurized in boron under shock compression. Our results also indicate that there exists an anomaly and negative Clapeyron slope along the melting curve of boron at 100GPa and 1500-3000 Kelvin. These results enable in-depth understanding of matter under shock compression, in particular the significance of compressionrate dependence of phase transitions and kinetic effects in experimental measurements.