Choong-Shik Yoo

Seoul National University, Seoul, Seoul, South Korea

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Publications (58)202.46 Total impact

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    ABSTRACT: Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; 3O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the Earth's lower mantle.
    Proceedings of the National Academy of Sciences 07/2008; 105(23):7925-9. · 9.74 Impact Factor
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    ABSTRACT: At high pressures and temperatures, CO2 transforms to a series of solid polymorphs with differing crystal structures, intermolecular interactions and chemical bonding. Among them are a number of covalent (extended) solid phases, with crystal structures analogous to SiO2 polymorphs. Above 40GPa and 1500K CO2 transforms to phase V, a network of corner sharing CO4 tetrahedra -- structurally similar to SiO2 tridymite. At room temperatures, CO2 forms a-carbonia, an amorphous extended-solid phase similar to silica glass. Recently, we reported another phase, with a structure resembling that of SiO2 stishovite, formed by compressing associated phase II above 50GPa. Here, we present a systematic picture of the structural and bonding diagram of carbon dioxide, focusing on the relationship between its molecular and extended phases at high pressures and temperatures.
    03/2008;
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    ABSTRACT: In this LDRD, we examined in detail the pressure-induced bonding and local coordination changes leading to the molecular {yields} associated {yields} extended-solid transitions in carbon dioxide (CO{sub 2}). We studied the progressive delocalization of electrons from the C=O molecular double bond at high pressures and temperatures, and determined the phase stability and physical properties of a new extended-solid CO{sub 2} phase (VI). We find that the new CO{sub 2} phase VI is based on a network of six-fold coordinated (octahedral) CO{sub 6} structures similar to the ultra-hard SiO{sub 2} phase stishovite.
    02/2008;
  • Choong-Shik Yoo, Brian Maddox, Valentin Iota
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    ABSTRACT: Unusual phase transitions driven by electron correlation effects occur in many f-electron metals (lanthanides and actinides alike) from localized phases to itinerant phases at high pressures. The dramatic changes in atomic volumes and crystal structures associated with some of these transitions signify equally important changes in the underlying electronic structure of these correlated f-electron metals. Yet, the relationships among the crystal structure, electronic correlation and electronic structure in f-electron metals have not been well understood. In this study, utilizing recent advances in third-generation synchrotron x-ray spectroscopies and high-pressure diamond-anvil cell technologies, we describe the pressure-induced spectral changes across the volume collapse transition in Gd at 60 GPa and well above. The spectral results suggest that the f-electrons of high-pressure Gd phases are highly correlated even at 100 GPa – consistent with the Kondo volume collapse model and the recent experimental evidence of strong electron correlation of α-Ce.
    MRS Proceedings. 12/2007; 1104.
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    ABSTRACT: Properties of the lower-mantle minerals such as ferropericlase [(Mg,Fe)O], silicate perovskite [(Mg,Fe)SiO3], and post-perovskite are affected by the electronic valence and spin states of iron, but the electronic states of iron under representative pressures and temperatures of the lower mantle have not yet been probed. Here the spin states of iron in lower-mantle ferropericlase and its crystal structure have been measured up to 95 GPa and 2000 K with x-ray emission and x-ray diffraction in a laser-heated diamond cell. Results show that an isosymmetric spin crossover of iron occurs over a wide pressure-temperature range extending from the middle part to the lower part of the lower mantle. The spin transition zone of iron in the lower-mantle phases significantly affects its implications for the geophysics, geochemistry, and geodynamics of the lower mantle. In particular, as the spin crossover of iron occurs in the lower-mantle minerals such as ferropericlase at high pressures and temperatures, their thermal compression curves, sound velocities, and transport properties will be continuously influenced by the ratio of the high-spin and low-spin states along the lower-mantle geotherm. Using recent results on the effects of the spin transitions on the density, elasticity, sound velocities, electrical conductivity, and strength of the lower-mantle phases, we will address how the electronic spin states in lower-mantle phases and their associated effects affect our understanding of the composition, geophysics, and dynamics of the lower mantle. This work was performed under the auspices of the U.S. DOE by UC\LLNL under Contract W-7405-Eng- 48.
    AGU Fall Meeting Abstracts. 12/2007;
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    ABSTRACT: One fascinating high-pressure behavior of tetrahedral glasses and melts is the local coordination change with increasing pressure, which provides a structural basis for understanding numerous anomalies in their high-pressure properties. Because the coordination change is often not retained upon decompression, studies must be conducted in situ. Previous in situ studies have revealed that the short-range order of tetrahedrally structured glasses and melts changes above a threshold pressure and gradually transforms to an octahedral form with further pressure increase. Here, we report a thermal effect associated with the coordination change at given pressures and show distinct thermal behaviors of GeO(2) glass in tetrahedral, octahedral, and their intermediate forms. An unusual thermally induced densification, as large as 16%, was observed on a GeO(2) glass at a pressure of 5.5 gigapascal (GPa), based on in situ density and x-ray diffraction measurements at simultaneously high pressures and high temperatures. The large thermal densification at high pressure was found to be associated with the 4- to 6-fold coordination increase. Experiments at other pressures show that the tetrahedral GeO(2) glass displayed small thermal densification at 3.3 GPa arising from the relaxation of intermediate range structure, whereas the octahedral glass at 12.3 GPa did not display any detectable thermal effects.
    Proceedings of the National Academy of Sciences 10/2007; 104(37):14576-9. · 9.74 Impact Factor
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    ABSTRACT: Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron occurs over a pressure-temperature range extending from about 1000 kilometers in depth and 1900 kelvin to 2200 kilometers and 2300 kelvin in the lower mantle. Because low-spin ferropericlase exhibits higher density and faster sound velocities relative to the high-spin ferropericlase, the observed increase in low-spin (Mg,Fe)O at mid-lower mantle conditions would manifest seismically as a lower-mantle spin transition zone characterized by a steeper-than-normal density gradient.
    Science 10/2007; 317(5845):1740-3. · 31.20 Impact Factor
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    ABSTRACT: We have developed a unique device, a dynamic diamond anvil cell (dDAC), which repetitively applies a time-dependent load/pressure profile to a sample. This capability allows studies of the kinetics of phase transitions and metastable phases at compression (strain) rates of up to 500 GPa/s (approximately 0.16 s(-1) for a metal). Our approach adapts electromechanical piezoelectric actuators to a conventional diamond anvil cell design, which enables precise specification and control of a time-dependent applied load/pressure. Existing DAC instrumentation and experimental techniques are easily adapted to the dDAC to measure the properties of a sample under the varying load/pressure conditions. This capability addresses the sparsely studied regime of dynamic phenomena between static research (diamond anvil cells and large volume presses) and dynamic shock-driven experiments (gas guns, explosive, and laser shock). We present an overview of a variety of experimental measurements that can be made with this device.
    Review of Scientific Instruments 08/2007; 78(7):073904. · 1.60 Impact Factor
  • Bruce J Baer, William J Evans, Choong-Shik Yoo
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    ABSTRACT: Coherent anti-Stokes Raman spectroscopy has been used to study deuterium at ambient temperature to 187 GPa, the highest pressure this technique has ever been applied. The pressure dependence of the nu1 vibron line shape indicates that deuterium has a rho direct=0.501 and rho exciton=0.434 mol/cm3 for a band gap of 2omega P=4.66 eV. The extrapolation from the ambient pressure band gap yields a metallization pressure of 460 GPa, confirming earlier measurements. Above 143 GPa, the Raman shift data provide clear evidence for the presence of the ab initio predicted I' phase of deuterium.
    Physical Review Letters 07/2007; 98(23):235503. · 7.94 Impact Factor
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    Geun Woo Lee, William J Evans, Choong-Shik Yoo
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    ABSTRACT: Crystal growth mechanisms are crucial to understanding the complexity of crystal morphologies in nature and advanced technological materials, such as the faceting and dendrites found in snowflakes and the microstructure and associated strength properties of structural and icy planetary materials. In this article, we present observations of pressure-induced ice VI crystal growth, which have been predicted theoretically, but had never been observed experimentally to our knowledge. Under modulated pressure conditions in a dynamic-diamond anvil cell, rough single ice VI crystal initially grows into well defined octahedral crystal facets. However, as the compression rate increases, the crystal surface dramatically changes from rough to facet, and from convex to concave because of a surface instability, and thereby the growth rate suddenly increases by an order of magnitude. Depending on the compression rate, this discontinuous jump in crystal growth rate or "shock crystal growth" eventually produces 2D carpet-type fractal morphology, and moreover dendrites form under sinusoidal compression, whose crystal morphologies are remarkably similar to those predicted in theoretical simulations under a temperature gradient field. The observed strong dependence of the growth mechanism on compression rate, therefore, suggests a different approach to developing a comprehensive understanding of crystal growth dynamics.
    Proceedings of the National Academy of Sciences 06/2007; 104(22):9178-81. · 9.74 Impact Factor
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    ABSTRACT: In the paper ''Sound velocities of ferropericlase in the Earth's lower mantle'' by, we regret that a factor of (1/2)^1/3 was mistakenly unaccounted for in converting the Debye sound velocities to km/s unit. The correct figures of the derived Vp , Vs , and G are presented here. The derived Vp , Vs , and G at ambient conditions are now lower than that of ultrasonic measurements. The difference may arise from the choice of the energy range for deriving the Debye sound velocities, in combination with the energy resolution of the partial phonon density of states in our study. Further analyses to resolve the difference are forthcoming and will be presented elsewhere. Other parts of the original article, including the discussion, remain unchanged.
    Geophysical Research Letters 05/2007; 34. · 3.98 Impact Factor
  • Bruce Baer, William Evans, Choong-Shik Yoo
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    ABSTRACT: High density (> 0.3 mol/cm^3) hydrogen and its isotopes have been studied intensely over the past three decades. Although many spectroscopic methods have been applied, none utilizes a multiphoton technique. Coherent anti-Stokes Raman Spectroscopy (CARS) has now been applied to samples over one megabar for the first time to accurately determine the density at which the bandgap of deuterium is 4.66 eV. This method yields very precise Raman shifts, linewidths and third order polarizability ratios since it avoids the problems associated with strain induced diamond fluorescence above a megabar. The pressure dependent third order polarizability ratios can indicate the location of the bandgap. We will present evidence for extrapolating the metallization pressure using these results and the implications on the phase diagram. This work has been supported by the LDRD and PDRP programs at Lawrence Livermore National Laboratory, University of California under the auspices of the U.S. Department of Energy under Contract No. W-7405-ENG-48.
    03/2007;
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    ABSTRACT: Under standard conditions, carbon dioxide (CO2) is a simple molecular gas and an important atmospheric constituent, whereas silicon dioxide (SiO2) is a covalent solid, and one of the fundamental minerals of the planet. The remarkable dissimilarity between these two group IV oxides is diminished at higher pressures and temperatures as CO2 transforms to a series of solid phases, from simple molecular to a fully covalent extended-solid V, structurally analogous to SiO2 tridymite. Here, we present the discovery of an extended-solid phase of CO2: a six-fold coordinated stishovite-like phase VI, obtained by isothermal compression of associated CO2-II (refs 1,2) above 50 GPa at 530-650 K. Together with the previously reported CO2-V (refs 3-5) and a-carbonia, this extended phase indicates a fundamental similarity between CO2 (a prototypical molecular solid) and SiO2 (one of Earth's fundamental building blocks). We present a phase diagram with a limited stability domain for molecular CO2-I, and suggest that the conversion to extended-network solids above 40-50 GPa occurs via intermediate phases II (refs 1,2), III (refs 7,8) and IV (refs 9,10). The crystal structure of phase VI suggests strong disorder along the c axis in stishovite-like P42/mnm, with carbon atoms manifesting an average six-fold coordination within the framework of sp3 hybridization.
    Nature Material 02/2007; 6(1):34-8. · 35.75 Impact Factor
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    ABSTRACT: The authors present a systematic study of high-pressure effects on electronic structure and magnetism in 3d transition metals (Fe, Co, and Ni) based on x-ray magnetic circular dichroism measurements. The data show that the net magnetic moment in Fe vanishes above 18 GPa upon the transition to hcp Fe, while both cobalt and nickel remain ferromagnetic to well over 100 GPa. The authors estimate the total disappearance of moment in hcp Co at around 150 GPa and predict a nonmagnetic Ni phase above 250 GPa. The present data suggest that the suppression of ferromagnetism in Fe, Co, and Ni is due to pressure-induced broadening of the 3d valence bands.
    Applied Physics Letters 01/2007; 90(4):042505-042505-3. · 3.79 Impact Factor
  • Choong-Shik Yoo, William Evans, Geun-Woo Lee
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    ABSTRACT: While diamond anvil cells (DACs) and gas-guns are capable of generating high pressures to 300-400 GPa, the precise and tunable control of de/compression rates has been a formidable challenge to both static and dynamic high-pressure research. Furthermore, the pressure-induced polymerization, amorphorization, and diffusion controlled crystal growth occur at an intermediate time scale (micro-to-millisecond) of conventional shock and static experiments, for which no compression technology is readily available for in-situ studies. To address this situation, we have recently developed dynamic-DAC (d-DAC) capable of precise controlling of pressure and compression rates at high static pressures. Coupling with time-resolved synchrotron x-ray, optical microscopy, and laser spectroscopy, d-DAC enables one to measure time-resolved structural evolutions of a sample across melting and other phase transitions. In this paper, following the brief description of dynamic-DAC, we will present our recent observations in d-DAC including shock crystal growth of ice VI dendrites and ice VII metastably grown from the stability field of ice VI.
    01/2007;
  • Geun Woo Lee, William Evans, Choong-Shik Yoo
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    ABSTRACT: The kinetics of phase transformation depends on how driving parameters are applied. Under high pressure, compression rate can give different paths of phase transformation. For this purpose, we have developed a new device, called dynamic diamond anvil cell (d-DAC), which can modulate a given static pressure with various compression rate and type. Using d-DAC, liquid water can be overpressurized up to 75 % in ice VI phase field without crystallization, and after transforms to metastable iceVII phase in the stable ice VI pressure field. Interestingly, when fast sinusoidal compression is applied, the crystal morphology of ice VI surrounded by liquid water dramatically changes to fractal and dendritic shape. In this talk, we will describe the details of crystallization, following a brief description of the technical development of d-DAC.
    01/2007;
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    ABSTRACT: Knowledge of the electronic structure of amorphous and liquid silica at high pressures is essential to understanding their complex properties ranging from silica melt in magma to silica glass in optics, electronics, and material science. Here we present oxygen near K-edge spectra of SiOâ glass to 51 GPa obtained using x-ray Raman scattering in a diamond-anvil cell. The x-ray Raman spectra below â10 GPa are consistent with those of quartz and coesite, whereas the spectra above â22 GPa are similar to that of stishovite. This pressure-induced spectral change indicates an electronic bonding transition occurring from a fourfold quartzlike to a sixfold stishovitelike configuration in SiOâ glass between 10 GPa and 22 GPa. In contrast to the irreversible densification, the electronic bonding transition is reversible upon decompression. The observed reversible bonding transition and irreversible densification call for a coherent understanding of the transformation mechanism in compressed SiOâ glass.
    Physical Review B 01/2007; 75(1):012201-012201. · 3.77 Impact Factor
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    ABSTRACT: Lithium borocarbide, which is a structural and electrical analog to high-Tc superconductor MgB2, remains insulating at ambient conditions due to atomic alternation in the crystal structure. We investigated experimentally and theoretically the properties of this material under pressure, including structural and bonding anisotropy and the possibility of metallization and superconductivity under high pressure. It is found to remain stable up to 60 GPa with no crystal structure change and without a previously reported lattice parameter anomaly. In this crystal structure, metallization is not predicted to occur until at least 345 GPa, at which pressure the electronic bands responsible for superconductivity in MgB2 remain unoccupied in LiBC, ruling out the possibility of a new MgB2-like high pressure superconductor.
    01/2007;
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    ABSTRACT: Electrical conductivity of the lower-mantle ferropericlase-(Mg0.75,Fe0.25)O has been studied using designer diamond anvils to pressures over one megabar and temperatures up to 500 K. The electrical conductivity of (Mg0.75,Fe0.25)O gradually rises by an order of magnitude up to 50 GPa but decreases by a factor of approximately three between 50 to 70 GPa. This decrease in the electrical conductivity is attributed to the isosymmetric high-spin to low-spin transition of iron in ferropericlase. That is, the electronic spin transition of iron results in a decrease in the mobility and/or density of the charge transfer carriers in the low-spin ferropericlase. The activation energy of the low-spin ferropericlase is 0.27 eV at 101 GPa, consistent with the small polaron conduction (electronic hopping, charge transfer). Our results indicate that low-spin ferropericlase exhibits lower electrical conductivity than high-spin ferropericlase, which needs to be considered in future geomagnetic models for the lower mantle.
    Geophysical Research Letters - GEOPHYS RES LETT. 01/2007; 34(16).
  • Zsolt Jenei, Jung-Fu Lin, Choong-Shik Yoo
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    ABSTRACT: Nitrogen is a typical molecular solid with relatively weak van der Waals intermolecular interactions but strong intramolecular interaction arising from the second highest binding energy of all diatomic molecules. The phase diagram of solid nitrogen is, however, complicated at high pressures, as inter-molecular interaction becomes comparable to the intra-molecular interaction. In this paper, we present an updated phase diagram of the nitrogen in the pressure-temperature region of 100 GPa and 1000 K, based on in-situ Raman and synchrotron x-ray diffraction studies using externally heated membrane diamond anvil cells. While providing an extension of the phase diagram, our results indicate a ``steeper'' slope of the delta/ε phase boundary than previously determined^1. We also studied the stability of the ε phase at high pressures and temperatures. Our new experimental results improve the understanding of the Nitrogen phase diagram. 1. Gregoryanz et al, Phys. Rev. B 66, 224108 (2002)
    01/2007;

Publication Stats

249 Citations
246 Downloads
202.46 Total Impact Points

Institutions

  • 2008
    • Seoul National University
      • Department of Earth and Environmental Sciences
      Seoul, Seoul, South Korea
  • 2006–2008
    • Washington State University
      • Institute for Shock Physics (ISP)
      Pullman, Washington, United States
    • University of Nevada, Las Vegas
      Las Vegas, Nevada, United States
  • 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