Synthesis of calcium orthocarbonate, Ca2CO4-Pnma at P-T conditions of Earth’s transition zone and lower mantle

Jannes Binck; Dominique Laniel; Lkhamsuren Bayarjargal; Saiana Khandarkhaeva; Timofey Fedotenko; Andrey Aslandukov; Konstantin Glazyrin; Victor Milman; Stella Chariton; Vitali B. Prakapenka; Natalia Dubrovinskaia; Leonid Dubrovinsky; Björn Winkler

doi:10.2138/am-2021-7872

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Synthesis of calcium orthocarbonate, Ca2CO4-Pnma at P-T conditions of Earth’s transition zone and lower mantle

Authors

Binck, Jannes¹
Laniel, Dominique²
Bayarjargal, Lkhamsuren¹
Khandarkhaeva, Saiana³
Fedotenko, Timofey²
Aslandukov, Andrey²
Glazyrin, Konstantin⁴
Milman, Victor⁵
Chariton, Stella⁶
Prakapenka, Vitali B.⁶
Dubrovinskaia, Natalia²
Dubrovinsky, Leonid³
Winkler, Björn¹

¹ Institut für Geowissenschaften, Goethe-Universität Frankfurt, Altenhöferallee 1, 60438 , (Germany)
² Laboratory of Crystallography, University of Bayreuth, 95440 , (Germany)
³ Bayerisches Geoinstitut, University of Bayreuth, 95440 , (Germany)
⁴ Photon Science, Deutsches Elektronen-Synchrotron, Notkestrasse 85, 22607 , (Germany)
⁵ BIOVIA Dassault Systèmes, 334 Science Park, CB4 0WN , (United Kingdom)
⁶ Center for Advanced Radiation Sources, The University of Chicago, Illinois 60637 , (United States)

Type

Published Article

Journal

American Mineralogist

Publisher

Mineralogical Society of America

Publication Date

Feb 25, 2022

Volume

107

Issue

3

Pages

336–342

Identifiers

DOI: 10.2138/am-2021-7872

Source

De Gruyter

Keywords

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Abstract

We show, by single-crystal diffraction studies in laser-heated diamond-anvil cells, that Ca2CO4 orthocarbonate, which contains CO44− tetrahedra, can be formed already at ~20 GPa at ~1830 K, i.e., at much lower pressures than other carbonates with sp3-hybridized carbon. Ca2CO4 can also be formed at ~89 GPa and ~2500 K. This very broad P-T range suggests the possible existence of Ca2CO4 in the Earth’s transition zone and in most of the lower mantle. Raman spectroscopy shows the typical bands associated with tetrahedral CO44−-groups. DFT-theory based calculations reproduce the experimental Raman spectra and indicate that at least in the athermal limit the phase assemblage of Ca2CO4 + 2SiO2 is more stable than 2CaSiO3 + CO2 at high pressures.

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