Choong-Shik Yoo

Washington State University, Pullman, Washington, United States

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Publications (105)339.07 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present the discovery of a novel nitrogen phase synthesized using laser-heated diamond anvil cells at pressures between 120-180 GPa well above the stability field of cubic gauche (cg)-N. This new phase is characterized by its singly bonded, layered polymeric (LP) structure similar to the predicted Pba2 and two colossal Raman bands (at ∼1000 and 1300 cm^{-1} at 150 GPa), arising from two groups of highly polarized nitrogen atoms in the bulk and surface of the layer, respectively. The present result also provides a new constraint for the nitrogen phase diagram, highlighting an unusual symmetry-lowering 3D cg-N to 2D LP-N transition and thereby the enhanced electrostatic contribution to the stabilization of this densely packed LP-N (ρ=4.85 g/cm^{3} at 120 GPa).
    Physical Review Letters 11/2014; 113(20):205502. · 7.73 Impact Factor
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    ABSTRACT: Dense nitrogen exhibits fascinating molecular and extended polymorphs as well as an anomalous melt maximum at high temperatures. However, the exact solid-liquid phase boundary is still the subject of debate, as both creating and probing hot dense nitrogen, solid and fluid alike, poses unique experimental challenges. Raman studies of nitrogen were performed to investigate the melting curve and solid-solid phase transitions in the pressure-temperature range of 25 to 103 GPa and 300 to 2000 K. The solid-liquid phase boundary has been probed with time-resolved Raman spectroscopy on ramp heated nitrogen in diamond anvil cell (DAC), showing a melting maximum at 73 GPa and 1690 K. The solid-solid phase boundaries have been measured with spatially resolved micro-confocal Raman spectroscopy on resistively heated DAC, probing the δ-ɛ phase line to 47 GPa and 914 K. At higher pressures the θ-phase was produced upon a repeated thermal heating of the ζ-phase, yet no evidence was found for the ι-phase. Hence, the present results signify the path dependence of dense nitrogen phases and provide new constraints for the phase diagram.
    The Journal of Chemical Physics 06/2014; 140(24):244510. · 3.12 Impact Factor
  • Gilbert Collins, David S Moore, Choong-Shik Yoo
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    ABSTRACT: This second joint conference between the APS Topical Group on Shock Compression of Condensed Matter and the International Association for the Advancement of High Pressure Science and Technology (AIRAPT) demonstrates that static and dynamic compression of condensed matter continues to be a vibrant field of science and engineering. It is also by its nature an interdisciplinary field, incorporating chemistry, materials science, solid mechanics, plasma physics, and condensed matter physics, and utilizes theoretical, computational, and experimental tools. Recent years have brought about many advances in loading platforms, diagnostics, and computations that are leading to the emergence of many new avenues of research. These advances are also breathing new life into traditional topics such as equations of state, phase transformations, and chemistry at extreme conditions. The plenary lectures by Gennady Kanel, Karl Syassen, David Ceperley, Jon Eggert, Duck Young Kim, and Richard Kraus spanned the disciplines of static and dynamic high pressure physics and illustrated the breadth of the field. They also showed that interesting and important problems remain for researchers of the future to solve.
    Journal of Physics Conference Series 05/2014; 500(00):001001.
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    ABSTRACT: The 18th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter in conjunction with the 24th Biennial International Conference of the International Association for the Advancement of High Pressure Science & Technology (AIRAPT) was held at the Westin Hotel in Seattle, Washington from 7–12 July, 2013. This is only the second time that these two organizations have held a Joint Conference — the first was 20 years previous (1993) in Colorado Springs, Colorado. Seattle was chosen for this joint conference because of its central location for the world-wide attendees as well as its metropolitan vibrancy. The scientific program consisted of 858 scheduled presentations organized into 23 topical areas and included contributed (537), invited (95), and plenary (6) lectures, as well as two poster sessions with 110 posters each. The scientific focus of the Joint Conference was on fundamental and applied research topics related to the static or dynamic compression of condensed matter. This multidisciplinary field of research encompasses areas of physics, chemistry, materials science, mechanics, geophysics and planetary physics, and applied mathematics. Experimental, computational and theoretical studies all play important roles. The organizers endeavored to intertwine static and dynamic experimental alongside computational and theoretical studies of similar materials in the organization of the sessions. This goal was aided by the addition of three special focus sessions on deep carbon budget, high energy density materials, and dynamic response of materials.
    Journal of Physics Conference Series 05/2014; 500(00):001002.
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    ABSTRACT: We present recent time-resolved x-ray diffraction data obtained across the solidification of water to ice-VI and -VII at different compression rates. The structural evolution of ice-VI to ice-VII, however, is not a sharp transition, but occurs rather coarsely. The diffraction data shows an anisotropic compression behavior for ice VI; that is, the c-axis is more compressible than the a-axis at the same compression rate. Nevertheless, the present equations of state of both ice-VI and ice-VII obtained under dynamic loadings agree well with those previously obtained under static conditions. Hence, the present study demonstrates that time-resolved x-ray diffraction coupled with the dynamic-DAC is an effective method for investigating details of the structural response of materials over a wide range of well-controlled compression rates. Finally, we found the evidence for an X-ray induced chemical reaction of water and ice-VI. The impurities, produced by the x-ray induced chemical reaction, inhibit the formation of amorphous ice.
    Journal of Physics Conference Series 05/2014; 500(14):142006.
  • Gustav M. Borstad, Choong-Shik Yoo
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    ABSTRACT: We have investigated high-pressure behaviors of simple binary mixtures of NH3 and D2 to 50 GPa and CH4 and D2 to 30 GPa using confocal micro-Raman spectroscopy. The spectral data indicate strong proton exchange reactions occur in dense D2-NH3 mixture, producing different isotopes of ammonia such as NH3, NH2D, NHD2, and ND3. In contrast, the proton exchange process in dense D2-CH4 mixture is highly limited, and no vibration feature is apparent for deuterated methane. The vibrational modes of H2 isotopes in D2-NH3 are blue shifted from those of pure H2 isotopes, whereas the modes of D2-CH4 show overall agreement with those in pure D2 and CH4. In turn, this result advocates the presence of strong repulsion and thereby internal pressure in D2-NH3 mixture, which are absent in D2-CH4. In fact, the bond length of hydrogen molecules in D2-NH3, calculated from the present spectral data, is shorter than that observed in pure hydrogen - supporting the enhanced intermolecular interaction in the mixture. Comparing the present spectral results with those previously observed in D2-H2O mixtures further suggests that the strength of repulsive interaction or the magnitude of internal pressure in the mixtures is proportional to the strength of hydrogen bonding in H2O, NH3, and CH4 in decreasing order. Hence, we suggest that the proton exchange is assisted by hydrogen bonding in these molecules.
    The Journal of Chemical Physics 12/2013; 140(4). · 3.12 Impact Factor
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    Mihindra Dunuwille, Choong-Shik Yoo
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    ABSTRACT: Ammonium Nitrate (AN) is a fertilizer, yet becomes an explosive upon a small addition of chemical impurities. The origin of enhanced chemical sensitivity in impure AN (or AN mixtures) is not well understood, posing significant safety issues in using AN even today. To remedy the situation, we have carried out an extensive study to investigate the phase stability of AN and its mixtures with hexane (ANFO-AN mixed with fuel oil) and Aluminum (Ammonal) at high pressures and temperatures, using diamond anvil cells (DAC) and micro-Raman spectroscopy. The results indicate that pure AN decomposes to N2, N2O, and H2O at the onset of the melt, whereas the mixtures, ANFO and Ammonal, decompose at substantially lower temperatures. The present results also confirm the recently proposed phase IV-IV(') transition above 17 GPa and provide new constraints for the melting and phase diagram of AN to 40 GPa and 400°C.
    The Journal of Chemical Physics 12/2013; 139(21):214503. · 3.12 Impact Factor
  • Dane Tomasino, Choong-Shik Yoo
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    ABSTRACT: Solidification of hydrogen and deuterium has been studied under dynamic compression using dynamic-diamond anvil cell, time-resolved Raman spectroscopy, and fast micro-photography. Liquid H2 or D2 solidifies into a grain boundary free crystal grown from the outer edge of the sample chamber in 1–30 ms depending on the compression rate. The time scale of solidification agrees well with that of the discontinuous Raman shift across the liquid/solid phase boundary, underscoring a compression rate dependence of the solidification process. The crystal growth rates were measured to be 0.12–0.80 cm/s for H2 and 0.13–1.27 cm/s for D2, varying linearly with the compression rate.
    Applied Physics Letters 08/2013; 103(6). · 3.52 Impact Factor
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    ABSTRACT: High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ∼6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity.
    Proceedings of the National Academy of Sciences 07/2013; · 9.81 Impact Factor
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    ABSTRACT: We report the evidence of two different polymorphs for polymeric CO2-V in tridymitelike (VTD in P212121) and β-cristobalitelike (VCR in I-42d) structures. The VTD phase is produced by laser-heating phase III (Cmca) above 40 GPa, whereas the VCR phase by laser-heating highly compressed phase II (P42/mnm—iso-space group to stishovite) and IV (P41212—iso-space group to α-cristobalite) above 35 GPa. The density of the VCR (3.988 g/cm3) is ∼12% larger than that of the VTD (3.559 g/cm3) at 50 GPa, while the density difference reduces to ∼4% at ambient pressure. This results in a substantially smaller bulk modulus (Bo = 127 GPa, B′ = 5.6) for the VCR phase than that of the VTD (Bo = 270 GPa, B′ = 1.9). The smaller density of the VTD is due to the open structure of corner shared CO4 tetrahedra and a great level of distortion in C-O-C angles resulting in a highly buckled layer structure; yet, the structural relationship gives rise to the specific transition to occur depending on the initial phase, either displacively from phase IV to phase VCR or diffusively from phase III to phase VTD. The results also provide new constraints for the phase/chemical transformation diagram of carbon dioxide.
    Physical review. B, Condensed matter 06/2013; 87(21). · 3.66 Impact Factor
  • Choong-Shik Yoo
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    ABSTRACT: Carbon dioxide exhibits a richness of high-pressure polymorphs with a great diversity in intermolecular interaction, chemical bonding, and crystal structures. It ranges from typical molecular solids to fully extended covalent solids with crystal structures similar to those of SiO2. These extended solids of carbon dioxide are fundamentally new materials exhibiting interesting optical nonlinearity, low compressibility and high energy density. Furthermore, the large disparity in chemical bonding between the extended network and molecular structures results in a broad metastability domain for these phases to room temperature and almost to ambient pressure and thereby offers enhanced opportunities for novel materials developments. Broadly speaking, these molecular-to-non-molecular transitions occur due to electron delocalization manifested as a rapid increase in electron kinetic energy at high density. The detailed mechanisms, however, are more complex with phase metastabilities, path-dependent phases and phase boundaries, and large lattice strains and structural distortions - all of which are controlled by well beyond thermodynamic constraints to chemical kinetics associated with the governing phases and transitions. As a result, the equilibrium phase boundary is difficult to locate precisely (experimentally or theoretically) and is often obscured by the presence of metastable phases (ordered or disordered). This paper will review the pressure-induced transformations observed in highly compressed carbon dioxide and present chemistry perspectives on those molecular-to-non-molecular transformations that can be applied to other low-Z molecular solids at Mbar pressures where the compression energy rivals the chemical bond energies.
    Physical Chemistry Chemical Physics 04/2013; · 4.20 Impact Factor
  • Haoyan Wei, Choong-Shik Yoo
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    ABSTRACT: We have studied dynamic thermo-mechano-chemical responses of reactive metallic systems, both in clouds of small oxygen-free particles (∼1–10 μm in diameter) produced by fracturing Zr-rich bulk metallic glass and in pure Zr metal foils (∼25 μm thin), under thermal (laser ablation or pulse electrical heating) and mechanical loadings. The mechanical fracture/fragmentation and fragments reactions were time resolved using an integrated set of fast six-channel optical pyrometer, high-speed microphotographic camera, and time- and angle-resolved synchrotron x-ray diffraction. These small-scale tabletop real-time experiments performed on or near surfaces of reactive metals provide fundamental data, in atomistic scales or of particle clouds, regarding fragmentation mechanics, combustion mechanisms and kinetics, and dynamics of energy release under thermal and mechanical loadings. We present the results of pure Zr and Zr-rich amorphous metals, not only signifying diversified combustion mechanisms depending on microstructures, particle sizes, oxygen pressure, and ignition conditions but also providing fundamental data that can be used to develop and validate thermochemical and mechanochemical models for reactive materials.
    Journal of Materials Research 03/2013; 27(21). · 1.82 Impact Factor
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    ABSTRACT: We have studied the pressure-induced physical and chemical transformations of tetracyanoethylene (TCNE or C6N4) in diamond anvil cells using micro-Raman spectroscopy, laser-heating, emission spectroscopy, and synchrotron x-ray diffraction. The results indicate that TCNE in a quasi-hydrostatic condition undergoes a shear-induced phase transition at 10 GPa and then a chemical change to two-dimensional (2D) C=N polymers above 14 GPa. These phase and chemical transformations depend strongly on the state of stress in the sample and occur sluggishly in non-hydrostatic conditions over a large pressure range between 7 and 14 GPa. The x-ray diffraction data indicate that the phase transition occurs isostructurally within the monoclinic structure (P21∕c) without any apparent volume discontinuity and the C=N polymer is highly disordered but remains stable to 60 GPa-the maximum pressure studied. On the other hand, laser-heating of the C=N polymer above 25 GPa further converts to a theoretically predicted 3D C-N network structure, evident from an emergence of new Raman νs(C-N) at 1404 cm(-1) at 25 GPa and the visual appearance of translucent solid. The C-N product is, however, unstable upon pressure unloading below 10 GPa, resulting in a grayish powder that can be considered as nano-diamonds with high-nitrogen content at ambient pressure. The C-N product shows a strong emission line centered at 640 nm at 30 GPa, which linearly shifts toward shorter wavelength at the rate of -1.38 nm∕GPa. We conjecture that the observed red shift upon unloading pressure is due to increase of defects in the C-N product and thereby weakening of C-N bonds.
    The Journal of Chemical Physics 03/2013; 138(9):094506. · 3.12 Impact Factor
  • Ranga Dias, Choong-Shik Yoo
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    ABSTRACT: We have studied the pressure-induced structural and electronic phase transitions of crystalline GeS2 (P21/c) to 50 GPa, using micro-Raman spectroscopy and electrical resistivity measurements in diamond anvil cells. The result shows a steady decrease in resistivity to that a metal at around 40GPa. The visual appearance of GeS2 supports the insulator-metal transition: initially transparent GeS2 becomes opaque and eventually reflective with increasing pressure. The Raman and X-ray diffraction result indicates that the metallization is preceded by a structural phase transition.
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    ABSTRACT: We present time-resolved synchrotron x-ray diffraction to probe the {epsilon}-{delta} phase transition of iron during pulse-laser heating in a diamond anvil cell. The system utilizes a monochromatic synchrotron x-ray beam, a two-dimensional pixel array x-ray detector and a dual beam, double side laser-heating system. Multiple frames of the diffraction images are obtained in real-time every 22 ms over 500 ms of the entire pulse heating period. The results show the structural evolution of iron phases at 17 GPa, resulting in thermal expansion coefficient 1/V({Delta}V/{Delta}T){sub p} = 7.1 x 10{sup -6}/K for {epsilon}-Fe and 2.4 x 10{sup -5}/K for {gamma}-Fe, as well as the evidence for metastability of {gamma}-Fe at low temperatures below the {epsilon}-{gamma} phase boundary.
    Journal of Physics Conference Series 08/2012; 377(1).
  • Amartya Sengupta, Young-Jay Ryu, Choong-Shik Yoo
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    ABSTRACT: It has been shown that high-pressure polymorphs of simple materials often display novel thermal/mechanical/optical properties and can be recovered at ambient conditions with significant stability (or metastability). Therefore, high-pressure synthesis of such materials offers an avenue toward novel materials applications. However, the present high-pressure method of diamond-anvil cell (DAC) or large volume press (LVP) has a fairly limited use in this regard because of a small amount of sample or the lack of in-situ optical diagnostic, respectively. Hybridizing the merits of DAC and LVP, we have recently developed a simple yet unique device, called a Transparent Large Anvil Press (TLAP), which consists of an opposed diamond anvil cell and a Paris-Edinburgh press. Coupling with a wide range of optical diagnostics such as Raman spectroscopy and laser heating, the TLAP is capable of in-situ investigation and synthesis of a milligram quantity of cryogenic samples at high pressures and temperatures.
    Journal of Physics Conference Series 07/2012; 377(1).
  • Jing-Yin Chen, Choong-Shik Yoo
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    ABSTRACT: The phase diagram of water is both unusual and complex, exhibiting a wide range of polymorphs including proton-ordered or disordered forms. In addition, a variety of stable and metastable forms are observed. The richness of H2O phases attests the versatility of hydrogen bonded network structures that include kinetically stable amorphous ices. In addition, natural gas hydrates are observed upon cooling and/or pressurization. The structures of gas hydrates are quite different from ices, yet guest molecules are enclathrated inside hydrogen bonded water cages. Hence, the presence of small impurity molecules can affect strongly the behaviours of hydrogen bonding and alter the phase diagram and phase boundaries of H2O. In this paper, we report the effect of methane impurity on solidification and melting of H2O under dynamic loading conditions. The presence of impurity mainly affects the growth rate of metastable ice VII, slowing down from 1.4 m/s in pure H2O to 0.26 m/s in impure H2O, neither the occurrence of metastable ice VII nor the melting of ice VI.
    Journal of Physics Conference Series 07/2012; 377(1).
  • Jing-Yin Chen, Choong-Shik Yoo
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    ABSTRACT: We describe high-pressure kinetic studies of the formation and phase transitions of methane hydrates (MH) under dynamic loading conditions, using a dynamic-diamond anvil cell (d-DAC) coupled with time-resolved confocal micro-Raman spectroscopy and high-speed microphotography. The time-resolved spectra and dynamic pressure responses exhibit profound compression-rate dependences associated with both the formation and the solid-solid phase transitions of MH-I to II and MH-II to III. Under dynamic loading conditions, MH forms only from super-compressed water and liquid methane in a narrow pressure range between 0.9 and 1.6 GPa at the one-dimensional (1D) growth rate of 42 μm/s. MH-I to II phase transition occurs at the onset of water solidification 0.9 GPa, following a diffusion controlled mechanism. We estimated the activation volume to be -109±29 Å(3), primarily associated with relatively slow methane diffusion which follows the rapid interfacial reconstruction, or martensitic displacements of atomic positions and hydrogen bonds, of 5(12)6(2) water cages in MH-I to 4(3)5(12)6(3) cages in MH-II. MH-II to III transition, on the other hand, occurs over a broad pressure range between 1.5 and 2.2 GPa, following a reconstructive mechanism from super-compressed MH-II clathrates to a broken ice-filled viscoelastic solid of MH-III. It is found that the profound dynamic effects observed in the MH formation and phase transitions are primarily governed by the stability of water and ice phases at the relevant pressures.
    The Journal of Chemical Physics 03/2012; 136(11):114513. · 3.12 Impact Factor
  • Ranga Dias, Choong-Shik Yoo
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    ABSTRACT: We have studied the pressure-induced structural and electronic phase transitions of layered GeS (Pnma) to 30 GPa, using micro-Raman spectroscopy and electrical resistivity measurements in diamond anvil cells. The result shows a steady decrease in resistivity to that of metal at around 18 GPa. The visual appearance of GeS supports the insulator-metal transition: initially black GeS becomes opaque and eventually reflective with increasing pressure. The Raman result indicates that the metallization is preceded by a structural phase transition, presumably to the previously predicted Cmcm structure.
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    ABSTRACT: Under high pressure, simple molecular solids transform into nonmolecular (extended) solids as compression energies approach the energies of strong covalent bonds in constituent chemical species. Unlike molecular and extended phase transitions, these exhibit path dependent phases, phase boundaries, phase metastabilities, and structural distortions that lead to large uncertainties in both experimental and theoretical phase diagrams. Here we present experimental and theoretical evidence that carbon dioxide polymerizes to extended phase V at 20 GPa, indicating a substantially lower equilibrium phase boundary than previously suggested. Clearly, these results indicate extended structures are inherently more stable above 20 GPa and the presence of a strong activation barrier hindering the polymerization in the intermediate pressure region between 20 and 40 GPa. Further, the present results advocate a chemistry view of molecular to nonmolecular phase transitions governed by constraints to kinetics and local energy minima that go beyond thermodynamics and are analogous to the graphite-diamond transition.
    The Journal of Physical Chemistry C 01/2012; 116:2061-2067. · 4.84 Impact Factor

Publication Stats

729 Citations
339.07 Total Impact Points


  • 2006–2014
    • Washington State University
      • • Department of Chemistry
      • • Institute for Shock Physics (ISP)
      Pullman, Washington, United States
    • University of Nevada, Las Vegas
      Las Vegas, Nevada, United States
  • 2008
    • Seoul National University
      • Department of Earth and Environmental Sciences
      Seoul, Seoul, South Korea
  • 2007
    • Carnegie Institution for Science
      • Geophysical Laboratory
      Washington, WV, United States
  • 1998–2007
    • Lawrence Livermore National Laboratory
      • • Condensed Matter and Materials Division
      • • National Ignition Facility & Photon Science Directorate
      Livermore, California, United States