Polymeric phase V of carbon dioxide has not been recovered at ambient pressure and has a unique structure

Datchi, F.; Moog, Mathieu; Pietrucci, Fabio; Saitta, A. Marco

doi:10.1073/pnas.1619276114

Cited by 5 publications

(1 citation statement)

References 10 publications

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“…I-295K (Yoo et al, 1999) I-295K (Olinger, 1982) I-726K (Giordano & Datchi, 2007) II-300K (Yoo et al, 2002) II-295K III-295K (Yoo et al, 1999) IV-300K (Park et al, 2003) IV-726K (Giordano et al, 2007) IV-295K (Datchi et al, 2009) IV-638K (Datchi et al, 2009) VII-726K (Giordano et al, 2007) Lower pressure values have also been reported with phase V transforming directly to the fluid (Iota et al, 1999). Recently, phase V was claimed to be quenchable at ambient pressure and low temperature (Yong et al, 2016), but this conclusion was questioned because residual pressure was inferred by the frequency of the Raman modes of coexisting phase I (Datchi et al, 2017). The P-T conditions necessary for the attainment and its large stability range evidence the existence of a remarkably high energy barrier, which must be overcome to accomplish the chemical transformation from the molecular phases to phase V. This was recently demonstrated by synthesizing this phase just above 20 GPa by laser heating phase IV using Ti as a catalyst (Sengupta et al, 2012).…”

Section: Extended Covalent Phasesmentioning

confidence: 99%

Structural and Chemical Modifications of Carbon Dioxide on Transport to the Deep Earth

Santoro

Gorelli

Dziubek

et al. 2020

Geophysical Monograph Series

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The structural and chemical changes to which carbon dioxide is subjected with increasing pressure and temperature are discussed here with the purpose of following the modifications of this important geochemical material on proceeding from the Earth's surface down to the core-mantle boundary. The relevance of metastabilities, and then of kinetic controlled transformations, is evidenced in the P-T ranges characteristic of both molecular phases and extended covalently bonded structures. From a chemical point of view, this analysis highlights how the characterization of the melting of the extended structures would represent an important step to understand the role of this compound in the chemistry of the Earth's mantle.

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Section: Extended Covalent Phasesmentioning

confidence: 99%

Structural and Chemical Modifications of Carbon Dioxide on Transport to the Deep Earth

Santoro

Gorelli

Dziubek

et al. 2020

Geophysical Monograph Series

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Crystalline polymeric carbon dioxide stable at megabar pressures

et al. 2018

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Carbon dioxide is a widespread simple molecule in the Universe. In spite of its simplicity it has a very complex phase diagram, forming both amorphous and crystalline extended phases above 40 GPa. The stability range and nature of these phases are still debated, especially in view of their possible role within the deep carbon cycle. Here, we report static synchrotron X-ray diffraction and Raman high-pressure experiments in the megabar range providing evidence for the stability of the polymeric phase V at pressure-temperature conditions relevant to the Earth’s lowermost mantle. The equation of state has been extended to 120 GPa and, contrary to earlier experimental findings, neither dissociation into diamond and ε-oxygen nor ionization was observed. Severe deviatoric stress and lattice deformation along with preferred orientation are removed on progressive annealing, thus suggesting CO2-V as the stable structure also above one megabar.

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The phase diagram of carbon dioxide from correlation functions and a many-body potential

Chen

Alexandria

Pascal

2021

The Journal of Chemical Physics

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The phase stability and equilibria of carbon dioxide are investigated from 125–325 K and 1–10 000 atm using extensive molecular dynamics (MD) simulations and the Two-Phase Thermodynamics (2PT) method. We devise a direct approach for calculating phase diagrams, in general, by considering the separate chemical potentials of the isolated phase at specific points on the P–T diagram. The unique ability of 2PT to accurately and efficiently approximate the entropy and Gibbs energy of liquids allows for assignment of phase boundaries from relatively short (∼100 ps) MD simulations. We validate our approach by calculating the critical properties of the flexible elementary physical model 2, showing good agreement with previous results. We show, however, that the incorrect description of the short-range Pauli force and the lack of molecular charge polarization lead to deviations from experiments at high pressures. We, thus, develop a many-body, fluctuating charge model for CO2, termed CO2–Fq, from high level quantum mechanics (QM) calculations that accurately capture the condensed phase vibrational properties of the solid (including the Fermi resonance at 1378 cm−1) as well as the diffusional properties of the liquid, leading to overall excellent agreement with experiments over the entire phase diagram. This work provides an efficient computational approach for determining phase diagrams of arbitrary systems and underscores the critical role of QM charge reorganization physics in molecular phase stability.

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Polymeric phase V of carbon dioxide has not been recovered at ambient pressure and has a unique structure

Cited by 5 publications

References 10 publications

Structural and Chemical Modifications of Carbon Dioxide on Transport to the Deep Earth

Structural and Chemical Modifications of Carbon Dioxide on Transport to the Deep Earth

Crystalline polymeric carbon dioxide stable at megabar pressures

The phase diagram of carbon dioxide from correlation functions and a many-body potential

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