Amorphization and a Polymorphic Transformation of Boron Stimulated by High Dynamic Pressures

Phase transformation in boron under shock compression

“…As an example, in the diamond-anvil cell and x-ray diffraction experiments by Sanz et al [14], β-boron was the stable structure up to ∼100 GPa, at which point an amorphization structure was observed. Similarly, explosive shock and diffraction experiments by Molodets and co-authors [22,21] did not detect the occurrence of γ-B 28 boron over the pressure range of 20-90 GPa. Instead, the β-B 106 phase was found to be stabilized until amorphization occured at 90-115 GPa.…”

“…The observed amorphization in megabar-pressure experiments [14,21,22] is likely a product of competition between the thermodynamic barrier that slows down the process of phase transformation and the decreased dynamic stability of β boron at megabar pressures.…”

“…More recently, additional data have been obtained from experiments at large laser facilities, including liquid structure-factor measurements using x-ray radiography to 100-400 GPa [20] and warm dense matter EOS measurements of the Hugoniot at pressures as high as 5608 GPa [1]. Explosive shock experiments have also been performed to measure the electrical conductivity [21] and structural transformation using x-ray diffraction [22] and found amorphization of β boron when shock-compressed to 115 GPa. These recent laser-shock results [1,20] have been compared with highly accurate first-principles electronic structure methods, in particular density functional theory molecular dynamics (DFT-MD).…”