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10.1063/5.0085292 85 R. Knepper, S. Rupper, S. DeJong, M. P. Marquez, D. E. Kittell, R. L. Schmitt, and A. S. Tappan, "Investigating growth to detonation in vapor-deposited hexanitrostilbene and pentaerythritol tetranitrate films using high-throughput methods", J. Appl. Phys. Such investigations can be applied to a wide range of materials such as pure metals,[[23], [25], [27]] steels,[29] other metallic alloys[[15], [30], [32]] including additively manufactured alloys,[[34]] ceramics,[36] polymers,[37] energetic materials,[38] or nanoporous materials.[[39]] B. Equation of state and phase transitions under shock compression I In situ i x-ray diffraction (XRD) has been used to investigate the occurrence and nature of phase transitions upon shock compression at large laser facilities, synchrotron, and x-ray free electron lasers. 10.1063/5.0076869 52 P. E. Specht, W. Reinhart, and C. Scott Alexander, "Measurement of the Hugoniot and shock-induced phase transition stress in wrought 17-4 PH H1025 stainless steel", J. Appl. Phys. R. Armstrong, H. B. Radousky, R. A. Austin, O. Tschauner, S. Brown, A. E. Gleason, N. Goldman, E. Granados, P. Grivickas, N. Holtgrewe, M. P. Kroonblawd, H. J. Lee, S. Lobanov, B. Nagler, I. Nam, V. Prakapenka, C. Prescher, E. J. Reed, E. Stavrou, P. Walter, A. F. Goncharov, and J. L. Belof, "Highly ordered graphite (HOPG) to hexagonal diamond (lonsdaleite) phase transition observed on picosecond time scales using ultrafast x-ray diffraction", J. Appl. Phys. [Extracted from the article]

The phase diagram of sodium chloride (NaCl) under laser shock compression has been studied at Linac Coherent Light Source (LCLS) at the x-ray free-electron laser facility. Both solid–solid (B1 → B2) and solid–liquid (B2 → liquid) transitions have been observed along the Hugoniot over nanosecond time scales. By combining structural measurements through in situ x-ray diffraction, pressure determination through velocimetry, and a thermal equation-of-state, the shock-compressed data are used to constrain the phase diagram of NaCl. Transformation into the B2 phase is found to occur at 28(2) GPa, and B2–liquid coexistence is observed between 54(4) and 66(6) GPa, with near full melt at 66(6) GPa. Late-time pressure release from an initial shocked B2-state results in a B2 → B1 back transformation. Our results show agreement with previous static compression data, suggesting that the time scale for melting is very rapid and that equilibrium states in NaCl are being accessed over nanosecond time scales. A multiphase equation-of-state description of NaCl incorporated into a one-dimensional hydrocode is used to interpret pressure and temperature evolution over these rapid time scales. [ABSTRACT FROM AUTHOR]

Recent studies show a face-centered cubic (fcc) to body-centered cubic (bcc) transformation along the shock Hugoniot for several metals (i.e., Cu, Au, and Ag). Here, we combine laser-shock compression of Cu foils on nanosecond timescales with in situ x-ray diffraction (XRD) to examine the microstructural changes with stress. We study the fcc phase and the phase transition from fcc to bcc (pressures greater than 180 GPa). Textural analysis of the azimuthal intensities from the XRD images is consistent with transformation into the bcc phase through the Pitsch-distortion mechanism. We use embedded atom model molecular dynamics simulations to determine the stability of the bcc phase in pressure–temperature space. Our results indicate that the bcc phase is stabilized only at high temperatures and remains stable at pressures greater than 500 GPa. [ABSTRACT FROM AUTHOR]

Combining an x-ray free electron laser with a high-power laser driver enables the study of equations-of-state, high strain-rate deformation processes, structural phase transitions, and transformation pathways as a function of pressure to hundreds of GPa along different thermodynamic compression paths. Future high repetition-rate laser operation will enable data to be accumulated at >1 Hz, which poses a number of experimental challenges, including the need to rapidly replenish the target. Here, we present a combined shock compression and an x-ray diffraction study on epoxy (50% vol.)-crystalline grains (50% vol.) slurry targets, which can be fashioned into extruded ribbons for high repetition-rate operation. For shock-loaded NaCl-slurry samples, we observe pressure, density, and temperature states within the embedded NaCl grains consistent with observations from shock-compressed single-crystal NaCl. [ABSTRACT FROM AUTHOR]

Since Bridgman's discovery of five solid water (H.sub.2O) ice phases.sup.1 in 1912, studies on the extraordinary polymorphism of H.sub.2O have documented more than seventeen crystalline and several amorphous ice structures.sup.2,3, as well as rich metastability and kinetic effects.sup.4,5. This unique behaviour is due in part to the geometrical frustration of the weak intermolecular hydrogen bonds and the sizeable quantum motion of the light hydrogen ions (protons). Particularly intriguing is the prediction that H.sub.2O becomes superionic.sup.6-12--with liquid-like protons diffusing through the solid lattice of oxygen--when subjected to extreme pressures exceeding 100 gigapascals and high temperatures above 2,000 kelvin. Numerical simulations suggest that the characteristic diffusion of the protons through the empty sites of the oxygen solid lattice (1) gives rise to a surprisingly high ionic conductivity above 100 Siemens per centimetre, that is, almost as high as typical metallic (electronic) conductivity, (2) greatly increases the ice melting temperature.sup.7-13 to several thousand kelvin, and (3) favours new ice structures with a close-packed oxygen lattice.sup.13-15. Because confining such hot and dense H.sub.2O in the laboratory is extremely challenging, experimental data are scarce. Recent optical measurements along the Hugoniot curve (locus of shock states) of water ice VII showed evidence of superionic conduction and thermodynamic signatures for melting.sup.16, but did not confirm the microscopic structure of superionic ice. Here we use laser-driven shockwaves to simultaneously compress and heat liquid water samples to 100-400 gigapascals and 2,000-3,000 kelvin. In situ X-ray diffraction measurements show that under these conditions, water solidifies within a few nanoseconds into nanometre-sized ice grains that exhibit unambiguous evidence for the crystalline oxygen lattice of superionic water ice. The X-ray diffraction data also allow us to document the compressibility of ice at these extreme conditions and a temperature- and pressure-induced phase transformation from a body-centred-cubic ice phase (probably ice X) to a novel face-centred-cubic, superionic ice phase, which we name ice XVIII.sup.2,17. The atomic structure of H.sub.2O is documented at several million atmospheres of pressure and temperatures of several thousand degrees, revealing shockwave-induced ultrafast crystallization and a novel water ice phase, ice XVIII, with exotic superionic properties., Author(s): Marius Millot [sup.1] , Federica Coppari [sup.1] , J. Ryan Rygg [sup.1] [sup.2] , Antonio Correa Barrios [sup.1] , Sebastien Hamel [sup.1] , Damian C. Swift [sup.1] , Jon [...]

This work presents a structural study of shock-compressed states in Ag to 331 GPa, accessed via laser shock compression. Structures of the resulting crystalline phases and the average atomic distribution of the liquid state are determined using in situ x-ray diffraction. We employ structure factor analysis, adapted for a non-monochromatic x-ray source, to determine the density of the liquid phase from analysis of x-ray diffraction data for the first time in shock compressed Ag. We also present a detailed analysis of the crystalline phases, which shows good agreement with the phase boundaries reported in previous experimental and theoretical works. We utilize the whole powder pattern fitting approach implemented in the MAUD package to constrain stacking faults in the face centered cubic structure. We observe the ambient fcc structure up to a stress of 146 GPa before a transition to a body-centered cubic structure and liquid phase at 179 GPa, with full melting above 212 GPa. [ABSTRACT FROM AUTHOR]

Understanding giant impacts requires accurate description of how extreme pressures and temperatures affect the physical properties of the constituent materials. Here, we report shock experiments on two polymorphs of MgSiO 3: enstatite and bridgmanite (perovskite) crystals. We obtain pressure‐density shock equation of state to 14 Mbar and more than 9 g/cm 3, a 40% increase in density from previous data on MgSiO 3. Density‐functional‐theory molecular dynamics (DFT‐MD) simulations provide predictions for the shock Hugoniot curves for bridgmanite and enstatite and suggest that the Grüneisen parameter decreases with increasing density. The good agreement between the simulations and the experimental data, including for the shock temperature along the enstatite Hugoniot reveals that DFT‐MD simulations reproduce well the behavior of dense fluid MgSiO3. We also reveal a high optical reflectance indicative of a metal‐like electrical conductivity which supports the hypothesis that magma oceans may contribute to planetary magnetic field generation. Plain Language Summary: Deciphering the evolution of the early Earth requires a detailed understanding of the history of our planet formation and evolution. Much like for other planets in the solar system and beyond, giant impacts are thought to have played a key role in the Earth history including the formation of the moon and the intense climatic perturbations leading to the Cretaceous‐Paleogene extinction event. Computer simulations of giant impact are now becoming increasingly accurate thanks to ever‐growing supercomputing capabilities worldwide. Here we report new shock wave experiments on two different kinds of the Earth mantle's most abundant mineral MgSiO 3, together with simulations based on quantum theory of condensed matter. We find that under intense shockwave compression of several million atmospheres, shock‐induced heating and compression together transform the rocky minerals into dense, shiny fluid able to conduct electrical current and therefore perhaps contribute to magnetic field generation by dynamo effect in the early stages of the evolution of rocky planets and exoplanets. Key Points: Bridgmanite was shock compressed to the conditions of giant impacts that dominated the final phase of the solar system formationDFT molecular dynamics simulations reproduce well the experimental data under such extreme P‐T conditions relevant for giant impact modelsDense fluid MgSiO3 exhibits a metal‐like electrical conductivity which indicates that magma oceans may generate planetary magnetic field [ABSTRACT FROM AUTHOR]

Molybdenum (Mo) is a body-centered-cubic (bcc) transition metal that has widespread technological applications. Although the bcc transition elements are used as test cases for understanding the behavior of metals under extreme conditions, the melting curves and phase transitions of these elements have been the subject of stark disagreements in recent years. Here we use x-ray diffraction to examine the phase stability and melting behavior of Mo under shock loading to 450 GPa. The bcc phase of Mo remains stable along the Hugoniot until 380 GPa. Our results do not support previous claims of a shallow melting curve for molybdenum. [ABSTRACT FROM AUTHOR]

Molybdenum (Mo) is a transition metal with a wide range of technical applications. There has long been strong interest in its high-pressure behavior, and it is often used as standard for high-pressure experiments. Combining powder x-ray diffraction and dynamic ramp compression, structural and equation of state data were collected for solid Mo to 1 TPa (10 Mbar). Diffraction results are consistent with Mo remaining in the body-centered-cubic structure into the TPa regime. Stress-density data show that Mo under ramp loading is less compressible than the room-temperature isotherm but more compressible than the single-shock Hugoniot. [ABSTRACT FROM AUTHOR]