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Published on-line at 08:56:25 AM on Wednesday, April 4th, 2012

Partially collapsed cristobalite structure in the non molecular phase V in CO2

Roberto Bini, Federico Gorelli, Mario Santoro on ADVANCED METHODS IN MATERIALS PROCESSING DEFECTS (STUD APPL MECH)

LENS researchers finally reveal structure of CO2-V non molecular phase under the typical conditions of pressure and temperature of Earth's mantle.

Under extreme conditions of pressure and temperature CO2 enters in a new non molecular phase called CO2-V and discovered in 1999, but no experimental evidence of its structure has been available until now. Finally, as reported by the last PNAS issue, the group of Prof. Roberto Bini at LENS, with the collaboration of CNR (IFAC and IPCF institutes) and the Department of Chemistry of University of Florence, has definetely determined how carbon and oxygen atoms arrange themselves in typical Earth's mantle conditions.

The structure of CO2-V at 43 GPa. The first picture on the left shows the I42d structure obtained from the Rietveld refinement using the experimental XRD data. Above the unit cell along the c-axis is presented, showing the partially collapsed arrangement of the CO4 tetrahedra.

For one decade the structure of CO2-V has been controversial despite theoretical studies and simulations have been performed to predict some features of this phase. One experimental difficulty in these kind of experiments is to get a clean laser heating procedure, but recently a rather clean one was employed using a CO2 laser with no additional absorbers. Key tools for structural analysis has been synchrotron XRD, Raman and IR absorption spectroscopy, that have allowed to obtain a quantitative proof of the existence of tetrahedral coordination in CO2, which "definetely supports the close analogy between carbon and the other group IV elements in forming oxides". So, "CO2-V exhibits the same structure of other oxides or oxynitrides [...] which transform to the well known quartz-type structure at high pressure". All this knowledge on carbon behavior at various conditions so provide insights concerning segregation of carbon and oxygen in Earth's mantle.

This research was funded within the Deep Carbon Observatory project and performed thanks to the European Synchrotron Radiation Facility (ESRF) and the Laserlab Europe initiative.

Source: Proceedings of the National Academy of Sciences

  • Title:
  • Partially collapsed cristobalite structure in the non molecular phase V in CO2
  • Authors:
  • Santoro, Mario and Gorelli, Federico A. and Bini, Roberto and Haines, Julien and Cambon, Olivier and Levelut, Claire and Montoya, Javier A. and Scandolo, Sandro
  • Source:
  • PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES