Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session F7: Phase Transitons II |
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Chair: Jow-Lian Ding, Washington State University Room: Regency Ballroom F |
Monday, July 10, 2017 5:00PM - 5:30PM |
F7.00001: Shock-induced phase transformations in silicon: continuum and x-ray diffraction measurements Invited Speaker: Stefan Turneaure Silicon under static compression undergoes a sequence of structural transformations with increasing pressure [Mujica et al., Rev. Mod. Phys. 75, 863 (2003)]. Previous dynamic compression experiments on silicon using different drivers and various diagnostics have not provided observations of any high-pressure silicon crystal structures but have raised many questions. For example, impact loading of millimeter scale thickness Si(100) samples from 16-22 GPa results in the formation of 3 shock waves transmitted through the material [Turneaure and Gupta, Appl. Phys. Lett. 91, 201913 (2007)]. The first wave compresses the silicon elastically and at the HEL (9 GPa) the stress deviators are large. Inelastic deformation occurs in the second wave, but the mechanisms responsible for relaxation of the stress deviators are not understood. Continuum and x-ray diffraction (XRD) measurements demonstrate that the stress deviators remain nonzero between the HEL and the phase transformation stress [Turneaure and Gupta, J. Appl. Phys. 111, 026101 (2012)]; the role of the stress deviators on the structural changes in silicon is an open question. A large volume collapse occurs in the third (phase transformation) wave with the peak state stress-density being consistent with one of the high-pressure structures observed for statically compressed silicon, but the structure in the peak state could not be determined from earlier experiments. Using multi-frame powder XRD measurements at the Dynamic Compression Sector the crystal structure of polycrystalline and single crystal silicon shock compressed to 26 GPa (and then partially released to 19 GPa) was directly examined [Turneaure and Gupta, Phys. Rev. Lett. 117, 045502 (2016)]. Both polycrystalline and single crystal silicon were found to transform to the simple hexagonal structure under shock compression. An important finding was that shock compression of single crystal silicon resulted in a highly textured simple hexagonal phase. Comparison of diffraction simulations for textured simple hexagonal silicon with the measured diffraction patterns revealed the orientation relations between the ambient cubic diamond and simple hexagonal silicon structures. The experimental approach and analysis procedures are general, and are being used at the Dynamic Compression Sector to examine orientation relations between low and high-pressure structures in other shocked single crystal and textured materials. [Preview Abstract] |
Monday, July 10, 2017 5:30PM - 5:45PM |
F7.00002: Crystal structure and atomic vibrations of laser ramp-compressed Pb to 600 GPa A. Lazicki, J. R. Rygg, F. Coppari, R. G. Kraus, C. E. Wehrenberg, R. F. Smith, D. E. Fratanduono, D. G. Braun, D. C. Swift, G. W. Collins, J. H. Eggert Laser ramp-compression is an increasingly popular means for accessing high pressure states in a solid far out of the range of traditional static-compression experiments, for the purpose of probing the phase diagram and testing first-principles predictions. However, the effects of nanosecond compression rates on the kinetics of high pressure phase transformations and on the temperature are poorly constrained. Using x-ray diffraction at the NIF and Omega laser facilities, we have explored these effects for the Pb system, which has two well-known high pressure phase transitions and a melting curve established by previous static experiments [1,2]. We will present the results of diffraction measurements exploring the effect of dynamic compression on the phase boundaries by measuring in-situ crystal structure and constraining the mean squared atomic displacement, which has a direct correlation with temperature, using the Debye-Waller attenuation of diffraction peak intensities at high angle. [1] Vohra et al., PRB 42, 8651 (1990). [2] Dewaele et al., PRB 76, 144106 (2007). [Preview Abstract] |
Monday, July 10, 2017 5:45PM - 6:00PM |
F7.00003: Shear-induced Lowering of Phase Transitions in Dynamically Compressed Silicon E. E. McBride, A. Krygier, A. Ehnes, E. Galtier, M. Harman, Z. Konopkova, H.-J. Lee, H.-P. Liermann, B. Nagler, A. Pelka, M. Roedel, A. Schropp, R. F. Smith, C. Spindloe, D. Swift, F. Tavella, S. Toleikis, T. Tschentscher, J. Wark, A. Higginbotham Despite being the subject of numerous shock compression studies, the behavior of silicon under dynamic loading is vigorously debated [1-4]. The few studies that combine shock compression and X-ray diffraction have exclusively focused on ``normal'' X-ray geometry whereby X-rays are collected along the shock propagation direction, consequently sampling numerous strain states at once, greatly complicating both phase identification and studies of phase transition kinetics. Here, we present a novel setup performing in situ X-ray diffraction studies perpendicular to the shock propagation direction at the Matter at Extreme Conditions end station at LCLS. Combining the extremely bright microfocussed X-ray beam with a nanosecond drive laser, we unambiguously determine the character of each wave for the first time.$\backslash $pard[1] Graham et al., JPCS, 27, 9 (1966), [2] Turneaure {\&} Gupta, APL, 90, 051905 (2007) [3] Colburn et al., JAP, 43, 5007 (1972) [4] Gust {\&} Royce, JAP, 42, 1897 (1971) [Preview Abstract] |
Monday, July 10, 2017 6:00PM - 6:15PM |
F7.00004: Strength of Iron Under Dynamic Compression Arianna Gleason, Cindy Bolme, Sebastien Merkel, Kyle Ramos, Bob Nagler, Eric Galtier, Hae Ja Lee, Eduardo Granados, Akel Hashim, Dylan Rittman, Wendy Mao Strength, defined as the maximum shear stress that can be sustained before plastic (ductile) flow, is a fundamental materials property that is difficult to measure directly or predict using theoretical calculations. Similarly, textures in polycrystals provide important information regarding the plastic behavior and identification of dominant twinning or slip mechanisms. Here we present experiments performed at the Matter in Extreme Conditions end-station at the Linac Coherent Light Source, SLAC combining a laser-driven dynamic compression pump and X-ray free electron laser (XFEL) probe to measure the strength of iron up to 220 GPa under dynamic compression. Adopting an experimental geometry similar to that of radial diffraction, we measured diffraction at ~65$^{\circ}$ to the shock propagation direction and cover 180$^{\circ}$ azimuth range in an X-ray transmission geometry. From the time-resolved X-ray diffraction (XRD) we measure line-shifts in hcp-Fe and see the development of marked preferred orientation on compression following the principal Hugoniot. An assessment of our resolution for measuring the magnitude of deviatoric strain (Q) finds it to be ~0.001. This enables the ability to resolve bulk strengths in iron as low as ~1 GPa. [Preview Abstract] |
Monday, July 10, 2017 6:15PM - 6:30PM |
F7.00005: Dynamic X-ray Diffraction to study the shock-induced $\alpha -\varepsilon $ Phase Transition in Iron. Brittany Branch, Brian Jensen Iron undergoes a well-known polymorphic phase transformation from a ferromagnetic body-centered cubic ($\alpha $-phase) ground state to a non-magnetic hexagonal-closed pack ($\varepsilon $-phase) crystal structure at pressures exceeding 13 GPa. With the coupling of dynamic loading platforms and advanced light sources we were able to study the $\alpha $- $\varepsilon $ phase transition of iron using dynamic X-ray diffraction (XRD) now available at the Advanced Photon Source (APS). ~Specifically, front-surface plate impact experiments were performed using single and two-stage gun systems coupled to the X-ray beam line at the new Dynamic Compression Sector (DCS) at the APS.~ X-ray diffraction data obtained from multiple 80 picosecond width x-ray bunches were obtained for impact stresses that spanned the a-e region of the phase diagram.~ The experimental methods, results, and preliminary analysis will be presented.~ LA-UR - 17-21401 [Preview Abstract] |
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