Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F38: Materials in Extremes: Phase Transitions IFocus
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Sponsoring Units: DCOMP GSCCM DMP Chair: Jon Belof, Lawrence Livermore National Laboratory Room: LACC 501A |
Tuesday, March 6, 2018 11:15AM - 11:27AM |
F38.00001: Shock induced phase transformation of single crystal Silicon – Molecular dynamic investigations Nilanjan Mitra, Dipak Prasad At ambient temperature and pressure conditions, single crystal Si exists in a diamond cubic structure. Experimental investigation reports that Si can exist in many different phases (beta-tin, orthorhombic, HCP, FCC) under different pressure conditions. Molecular dynamic simulations have been carried out in this study upto 80 Gpa pressure to observe and characterize different phases of Si under shock compression. The characterization of different phases has been done using various mechanistic perspectives such as radial distribution function, neighbor based structural identification, x-ray diffraction etc. Two different interatomic potential -- Tersoff and Stillinger-Weber has been utilized to explore capability, accuracy and applicability of these potentials for typical dynamic shock study in three different directions <100>, <110> and <111>. |
Tuesday, March 6, 2018 11:27AM - 11:39AM |
F38.00002: High-Pressure High-Temperature Synthesis: a Path Towards New Hexagonal Polytypes of Silicon Silvia Pandolfi, Carlos Renero-Lecuna, Yann Le Godec, Michele Lazzeri, Benoit Baptiste, Nicolas Menguy, Christel Gervais, Kristina Spektor, Wilson Crichton, Oleksandr Kurakevych Technology is a ubiquitous component of modern life. Silicon is one of the main protagonists of this field, but its indirect bandgap imposes strict limitations on future performance improving. The most intriguing perspective for the future is bandgap engineering, accomplished by both nanostructuring or by modifying the crystal structure. Indeed, many metastable phases with properties suitable for applications have been predicted by ab-initio calculations; high-pressure could be an efficient technique and lead to the synthesis of new functional allotropes. |
Tuesday, March 6, 2018 11:39AM - 11:51AM |
F38.00003: Phase transition as a relaxation from shear stress in uniaxial compression Kento Katagiri, Norimasa Ozaki, Ryo Hazama, Takahiro Matsuoka, Takeshi Matsuoka, Kenjiro Takahashi, Kohei Miyanishi, Yusuke Seto, Yuichi Inubushi, Toshinori Yabuuchi, Tadashi Togashi, Makina Yabashi, Ryosuke Kodama In well-known phase transition mechanism under laser shocked material, highly and elastically strained lattice would be relaxed by plasticity as pressure inside of material exceeds Hugoniot Elastic Limit (HEL). Then phase transition to higher pressure state would come after the plastic deformation if enough pressure is given. In different phase transition mechanism we will present, highly strained lattice would be relaxed by transition itself, and requires lower laser energy and shorter transition time to synthesize higher pressure state. We would like to introduce this mechanism through the X-ray Free Electron Laser (XFEL) observation of phase transition in carbon materials. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F38.00004: Mysteries surrounding the carbon equation of state Lorin Benedict, Philip Sterne, Sebastien Hamel, Marius Millot For the past several years, various groups have performed shock and release measurements on carbon, starting from diamond initial states, which access fairly low-density, high-temperature regimes. Recent equation of state models for carbon constructed from ab initio electronic structure calculations seem to be in notable disagreement with these measurements. We will briefly review the current situation, after which we will discuss a few ways in which we have tried to better understand this conundrum. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F38.00005: Liquid Structure of Carbon and Hydrocarbons around 100 GPa and 5000 K Dominik Kraus Structural properties of liquid carbon and hydrocarbons at extreme pressures and temperatures are highly relevant for modelling the interiors of carbon-bearing planets as well as modern inertial confinement fusion concepts where plastic or carbon are used as ablator materials. Here we present dynamic compression experiments performed at the Linac Coherent Light Source that allow for experimentally determining the high-pressure liquid structure of these materials with high precision. We show that liquid carbon is dominated by a diamond-like structure close to the melting line. These strong carbon-carbon interactions lead to partial demixing in hydrocarbon samples at similar conditions. |
Tuesday, March 6, 2018 12:15PM - 12:51PM |
F38.00006: Phase transitions, including melting, during static and shock compression conditions Invited Speaker: Richard Briggs Extreme conditions of high pressure and high temperature can be achieved through static compression and the diamond anvil cell, or through dynamic shock/ramp techniques using high power lasers to reach P > 1 TPa. Studies of phase transitions under static compression have traditionally been carried out using a combination of DAC and synchrotron X-ray diffraction techniques. With the high energy and high flux of X-rays that a synchrotron can deliver, one can determine even complex crystal structures such as incommensurate host-guest structures through observations of diffraction peaks with very low relative intensities. Until recently, this has not been viable for shock compression studies even at moderate pressures. Powder XRD with image plates have been performed during ramp compression into the TPa pressure range, but only a few peaks are observed above the background noise. Now, with the advent of 4th generation light sources (X-ray FELs) ultrafast XRD experiments can be carried out with fs exposure times and sufficient flux to identify complex crystal structures and even diffuse liquid scattering during shock compression; these new results will be presented and discussed. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F38.00007: Observation of Compression-Induced Phase Transformations in Zirconium using Ultrafast X-Ray Diffraction Harry Radousky, Michael Armstrong, Jonathan Belof, Ryan Austin, Elissaios Stavrou, Shaughnessy Brown, Jonathan Crowhurst, Arianna Gleason, Eduardo Granados, Paulius Grivickas, Nicholas Holtgrewe, Haeja Lee, Tian Li, Sergey Lobanov, Joseph McKeown, Robert Nagler, Inhyuk Nam, Art Nelson, Vitali Prakapenka, Clemens Prescher, John Roehling, Nick Teslich, Peter Walter, Joseph Zaug, Alexander Goncharov The mechanisms of phase transitions in bulk materials are analogous to the transition state in the study of chemical reactions. Detailed knowledge of these mechanisms (and the ability to control them) has the potential to revolutionize material synthesis. Studying such phenomena is difficult, however, since the fundamental mechanisms of phase transitions occur on near-atomic (nm) length scales at the speed of sound (1-10 nm/ps for condensed phases), implying picosecond time scales. Using 130 fs x-rays at the LCLS-MEC beamline, we interrogated phase transformation pathways of Zr at the spatial and temporal scales of these fundamental mechanisms. Zr was dynamically compressed to pressures up to 130 GPa, driven by ~120 picosecond duration laser pulses with energies in the range of 2.5-250 mJ. We observed an intermediate body-centered cubic (bcc) β-Zr phase on the transformation path from the hexagonal close-packed (hcp) α-Zr phase towards the P6/mmm ω-Zr phase under rapid compression. At 33 GPa compression, we observed the initial α-Zr phase transform into the β-Zr phase, bypassing the lower-pressure ω-Zr phase. At 130 GPa, we observed direct melting of Zr from the α phase, followed by recrystallization on a longer ns timescale. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F38.00008: Simulation of phase transitions during shock waves in zirconium. Hongxiang Zong, Graeme Ackland Under ambient conditions, zirconium adopts the hcp structure, but under high pressure or temperature it can transform to bcc or a more complex omega phase. These transformations are martensitic, so can be expected to occur on the timescale of a shock wave. Simulation of this process has been hindered by the lack of a reliable interatomic potential which correctly describes the phase stability. All three phases are metallic, so a short-ranged model such as the embedded atom method describes the bonding, but the phase stability has proved more challenging to predict. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F38.00009: Laser induced ramp compression of Zr on nano-second scales Paulius Grivickas, Michael Armstrong, Jonathan Crowhurst, Harry Radousky, Joseph Zaug, Ryan Austin, Jonathan Belof Quasi-isentropic ramp waves are advantageous in resolving wave structures due to phase-transitions and other dissipative phenomena. An open question is how this behavior changes with strain rate and kinetics of material transformation. To address this question, we study how phase transitions in Zr are affected when ramp waves are induced by short laser pulses extending over 1-10 ns time scales. Measurements are performed in thin 0.2 – 10 um Zr films using several different experimental platforms. Velocimetry data is collected using the line VISAR interferometry and analyzed using the Lagrangian and forward simulation methods. The results obtained are being compared to the corresponding Hugoniot and isentrope curves reported in the literature at longer time scales. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F38.00010: High-Pressure X-ray Diffraction Structural Study of Zr: Reinvestigation of the Isostructural BCC→BCC Phase Transition and EOS Determination up to 210 GPa Elissaios Stavrou, Daniel Aberg, Per Soderlind, David Young, Harry Radousky, Michael Armstrong, Jonathan Belof, Martin Kunz, Vitali Prakapenka, Eran Greenberg Interplay between structural transitions and electronic and lattice dynamics properties under pressure is of one the fundamental issues in condensed matter physics. The structural evolution of Zr under pressure had attracted substantial interest due to the possibility of an isostructural BCC→BCC phase transition at 57 GPa. Akahama et al. suggested that this transition is triggered by a s-d electronic transition. Follow up theoretical studies ruled out the electronic transition and questioned the existence of the structural transition. In this study we have performed a detailed structural study of Zr up to 210 GPa. We confirm the isostructural transition and we don't observe any subsequent phase transition up to the highest pressure of this study. We have used density functional theory to investigate zirconium in the isostructural transition region. The pressure-volume curve is smooth, without any indication of a band crossing. DFT phonons have been calculated, and show no indication of anomalies that could drive a phase transition. A more comprehensive theoretical approach seems to be needed. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F38.00011: Radiance and Velocity Measurements on Shock-Ramp Loaded Tin Jeffrey Nguyen, Minta Akin, Paul Asimow, Neil Holmes We report here an updated analysis of a series of experiments on shock-ramp loaded tin. An accurate material temperature is not only an essential component of an equation of state, but also a good measure of a phase transition, its kinetics, and associated thermal transport properties. In a series of experiments, we measured particle velocity and thermal emission at the tin-LiF interfaces on shock and ramp loading experiments. Using a graded density impactor, we drive the tin sample through melting with the initial shock and then further ramp-compress it back into the solid phase. Various configurations of experimental set-up were used to simultaneously measure particle velocity and thermal emission from which we deduce pressure, density, sound velocity and temperature. A gray body radiation is assumed in these calculations. The measured particle velocity shows a traditional signature for phase transition, while thermal radiance exhibits a change consistent with the heat of solidification. We will discuss here the mechanical and thermal aspects of this phase transition, its kinetics, and thermal transport issues in this experiment. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F38.00012: Investigation of Electronic and Structural Properties of Tin Compounds under Extreme Pressure Daniel Sneed, Ashkan Salamat Many heavy metal oxides have been predicted to have unique electronic properties. One such material is SnO2, which is a wide band-gap semiconductor. SnO2 has been shown to have the unique property of its band gap opening with pressure. Utilizing a combination of X-ray diffraction, X-ray absorption, Raman, and UV absorption, we have attempted to probe this unique phenomenon. By combining these techniques with ground state structure predictions, along with Reverse Monte Carlo fitting to determine local order from EXAFS, we have begun to understand the structural and electronic configurations of SnO2. One difficulty with these measurements and analysis is that SnO2 is known to have kinetically hindered phase transitions. By utilizing in situ CO2 laser annealing at each pressure point, we have been able to access the true ground state structures that have been predicted from theoretical structure searching. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F38.00013: Dimerization in the III-V semiconductor gallium phosphide Barbara Lavina, Eunja Kim, Hyunchae Cynn, Philippe Weck We explored the high-pressure polymorphism of GaP using microdiffraction and first principles techniques. After laser heating at ~40 GPa and 1300 K we found that GaP assumes the super-Cmcm structure featuring the formation of short P-P dimers. A comparison of total energy and enthalpy suggests that the phase here proposed is more stable than earlier considered arrangements at 0K, it is therefore the best candidate high-pressure polymorph of GaP in the range ~ 20-40 GPa. The symmetry lowering is explained by the mixed nature of the bonding in the new phase. |
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