High-pressure phases of CaCO3: Crystal structure prediction and experiment |
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| Institution: | 1. Laboratory of Crystallography, Department of Materials, ETH Hönggerberg, HCI G 515, Wolfgang-Pauli-Str. 10, CH-8093 Zurich, Switzerland;2. Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061, Japan;1. Seismological Laboratory, California Institute of Technology, 1200 E California Blvd, MS 252-21, Pasadena, CA 91125, USA;2. Advanced Photon Source, Argonne National Laboratory, 9700 S Cass Ave, Argonne, IL 60439, USA;3. Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822, USA;5. GSECARS, University of Chicago, 9700 S Cass Ave, Argonne, IL 60439, USA;1. Laboratory of Seismology and Physics of Earth''s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;2. National Geophysical Observatory at Mengcheng, Anhui, China;1. Laboratory of Seismology and Physics of Earth''s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China;2. National Geophysical Observatory at Mengcheng, Anhui 233500, China;3. Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78712, USA;4. Key Laboratory for High Temperature and High Pressure Study of the Earth''s Interior of Institute of Geochemistry, CAS, Guiyang, Guizhou 550002, China;5. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Changchun, Jilin 130012, China;6. Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA;1. Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK;2. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai 201203, China;1. Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China;2. Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA;3. Center for High Pressure Science and Technology Advanced Research, Beijing 100094, China;4. Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road N.W., Washington, DC 20015, USA;5. Center for Advanced Radiation Sources, University of Chicago, IL 60637, USA;6. Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78712, USA;1. Laboratory of Seismology and Physics of Earth''s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China;2. National Geophysical Observatory at Mengcheng, University of Science and Technology of China, Hefei, China;3. CAS Center for Excellence in Comparative Planetology, China |
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| Abstract: | Post-aragonite phase of CaCO3, experimentally known to be stable above 40 GPa S. Ono, T. Kikegawa, Y. Ohishi, J. Tsuchiya, Post-aragonite phase transformation in CaCO3 at 40 GPa, Am. Mineral. 90 (2005) 667–671], is believed to be a major carbon-containing mineral in the Earth's mantle. Crystal structure of this mineral phase could not be solved using experimental data or traditional theoretical simulation methods and remained a controversial issue. Using a combination of advanced ab initio simulation techniques and high-pressure experiment, we have been able to determine the crystal structure of CaCO3 post-aragonite. Here, we performed simulations with the USPEX code C.W. Glass, A.R. Oganov, and N. Hansen, (in preparation). USPEX: a universal structure prediction program], which is based on an evolutionary algorithm using ab initio free energy as the fitness function. This novel methodology for crystal structure prediction, which uses only the chemical composition as input, is described in detail. For CaCO3, we identify a number of energetically competitive structures, the most stable of which closely matches the experimental powder diffraction pattern and, in agreement with experiment, becomes more stable than aragonite above 42 GPa. This structure belongs to a new structure type, which is also adopted by the high-pressure post-aragonite phases of SrCO3 and BaCO3. It has 2 formula units in the orthorhombic unit cell (space group Pmmn) and contains triangular CO32? ions and Ca2+ ions in the 12-fold coordination. Above 137 GPa, a pyroxene-type structure (space group C2221) with chains of CO44? tetrahedra becomes more stable than post-aragonite. For MgCO3, this structure becomes more stable than magnesite above 106 GPa and is a good candidate structure for MgCO3 post-magnesite. |
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