Phase transformation in boron under shock compression

Nature of the bonded-to-atomic transition in liquid silica to TPa pressures

“…In this work, the initial states are estimated by starting from DFT calculations at the desired densities (2.20, 2.65, and 4.29 g/cm 3 for fused silica, α-quartz, and stishovite, respectively) 49 , then we consider each isotherm with temperature T and fit the pressure and energy data along the isotherm as functions of density by using cubic splines 50 , and the density ρ at which the energy term [E − E i ] equals the pressure term [(P + P i )(V i − V )/2] defines the Hugoniot, which has definitive values in T, ρ, P and E. We also calculate the shock velocity u s and particle velocity u p , relevant to shock experiments, by u 2 s = ξ/η and u 2 p = ξη, where ξ = (P −P i )/ρ i and η = 1−ρ i /ρ. This approach has been used previously for calculating the Hugoniot of several other materials [51][52][53][54][55][56][57] , and was found to produce consistent Hugoniots with other computational methods, such as progressive determination by running a large number of EOS calculations around the Hugoniot curve 58,59 In order to cross check the validity of the Hugoniot results based on the relatively sparse temperature-density grid, we have recalculated the Hugoniot of α-quartz by performing 2D interpolation of the pressure and energy data as functions of (T, ρ) and then determined the conditions at which the function H(ρ, T ) = E − E i + (P + P i )(V − V i )/2 equals zero. We have also made tests by using a partial set of our EOS data (by excluding the 6.62 g/cm 3 isochore).…”

Structural Motifs and Bonding in Two Families of Boron Structures Predicted at Megabar Pressures

“…Moreover, experimental variables such as the temperature and compression mechanism (static vs. dynamic) can affect the phases that are formed. For boron, in particular, discrepancies between the measured and calculated shock Hugoniot, as well as the computed melting temperatures suggest that new post-α-Ga phases can be formed at megabar pressures [17].…”

“…Various stable and metastable polymorphs of elemental boron have been proposed as superhard [8][9][10], superconducting [11][12][13][14], and even topological materials [15]. Furthermore, because of its higher density and tensile strength as compared to plastics, this low-Z material offers an option as an ablator in inertial confinement fusion and high energy density experiments, and its phase behavior as a function of temperature and pressure is of extreme interest [16,17]. The structural chemistry of boron, including metastable phases that could be created in experiment, must be understood in order to accurately model its behavior under such conditions.…”

Phase transformation path in Aluminum under ramp compression; simulation and experimental study

“…In a recent work by Polsin et al 11 , in situ XRD were utilized to detect the crystal structure of Aluminum (Al) under ramp compression loading. The authors found out that a solid–solid phase transition, consistent with a transformation to a hexagonal close-packed (hcp) structure, occurs at around 216 GPa, while a transformation to a structure consistent with the body-centered cubic (bcc) structure occurs at 320 GPa.…”