Raman spectroscopy and x-ray diffraction of sp 3 CaC O 3 at lower mantle pressures

Sergey S. Lobanov, Xiao Dong, Naira S. Martirosyan, Artem I. Samtsevich, Vladan Stevanovic, Pavel N. Gavryushkin, Konstantin D. Litasov, Eran Greenberg, Vitali B. Prakapenka, Artem R. Oganov, Alexander F. Goncharov

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)

Abstract

The exceptional ability of carbon to form sp2 and sp3 bonding states leads to a great structural and chemical diversity of carbon-bearing phases at nonambient conditions. Here we use laser-heated diamond-anvil cells combined with synchrotron x-ray diffraction, Raman spectroscopy, and first-principles calculations to explore phase transitions in CaCO 3 at P>40GPa. We find that postaragonite CaCO 3 transforms to the previously predicted P21/cCaCO 3 with sp3-hybridized carbon at 105 GPa (∼30GPa higher than the theoretically predicted crossover pressure). The lowest-enthalpy transition path to P21/cCaCO 3 includes reoccurring sp2 and sp3CaCO 3 intermediate phases and transition states, as revealed by our variable-cell nudged-elastic-band simulation. Raman spectra of P21/cCaCO 3 show an intense band at 1025cm-1, which we assign to the symmetric C-O stretching vibration based on empirical and first-principles calculations. This Raman band has a frequency that is ∼20% lower than the symmetric C-O stretching in sp2CaCO 3 due to the C-O bond length increase across the sp2-sp3 transition and can be used as a fingerprint of tetrahedrally coordinated carbon in other carbonates.

Original languageEnglish
Article number104101
JournalPhysical Review B
Volume96
Issue number10
DOIs
Publication statusPublished - 1 Sep 2017

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