Scientific Results

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

Year: 2012

Authors: Santoro M., Gorelli F. A., Bini R., Haines J., Cambon O., Levelut C., Montoya J. A., Scandolo S.

Autors Affiliation: Istituto di Fisica Applicata Nello Carrara del Consiglio Nazionale delle Ricerche (IFAC-CNR), Sesto Fiorentino, 50019 Firenze, Italy;
European Laboratory for non Linear Spectroscopy (LENS), Sesto Fiorentino, 50019 Firenze, Italy;
Istituto dei Processi Chimico Fisici del Consiglio Nazionale delle Ricerche(IPCF-CNR), Unità Organizzativa di Supporto Roma, 00185 Rome, Italy;
Dipartimento di Chimica dell’Università di Firenze, Sesto Fiorentino, 50019 Firenze, Italy;
Institut Charles Gerhardt Montpellier, Unités Mixtes de Recherche 5253, Centre National de la Recherche Scientifique (CNRS), Equipe C2M, Université Montpellier 2, 34095 Montpellier cedex 5, France;
Laboratoire Charles Coulomb, Unités Mixtes de Recherche 5221, Centre National de la Recherche Scientifique (CNRS), Département Colloïdes, Verres et Nanomatériaux (CVN), Université Montpellier 2, 34095 Montpellier cedex 5, France;
Department of Geosciences, Princeton University, Princeton, NJ 08544;
Instituto de Matemáticas Aplicadas, Universidad de Cartagena, Calle 36, Centro, 30202, Bolivar, Colombia;
The Abdus Salam International Center for Theoretical Physics (ICTP), 34151 Trieste, Italy;
Istituto Officina dei Materiali del Consiglio Nazionale delle Ricerche (IOM-CNR), Democritos National Simulation Center, 34136 Trieste, Italy

Abstract: Non molecular CO2 has been an important subject of study in high pressure physics and chemistry for the past decade opening up a unique area of carbon chemistry. The phase diagram of CO2 includes several non molecular phases above 30 GPa. Among these, the first discovered was CO2-V which appeared silica-like. Theoretical studies suggested that the structure of CO2-V is related to that of beta-cristobalite with tetrahedral carbon coordination similar to silicon in SiO2, but reported experimental structural studies have been controversial. We have investigated CO2-V obtained from molecular CO2 at 40-50 GPa and T > 1500 K using synchrotron X-ray diffraction, optical spectroscopy, and computer simulations. The structure refined by the Rietveld method is a partially collapsed variant of SiO2 beta-cristobalite, space group I (4) over bar 2d, in which the CO4 tetrahedra are tilted by 38.4 degrees about the c-axis. The existence of CO4 tetrahedra (average O-C-O angle of 109.5 degrees) is thus confirmed. The results add to the knowledge of carbon chemistry with mineral phases similar to SiO2 and potential implications for Earth and planetary interiors.


Volume: 109 (14)      Pages from: 5176  to: 5179

More Information: We acknowledge the ESRF for provision of beam time at ID27; we thank M. Mezouar (ESRF) for discussions, and A. Salamat (ESRF) for his crucial help in setting up the laser heating procedure, in performing the XRD measurements, and for very useful discussions. We also acknowledge the support from the European Union [European Laboratory for non Linear Spectroscopy (LENS) Contract FP7 G. A. No. 228334 LASERLABEUROPE], the Ente Cassa di Risparmio di Firenze, the Deep Carbon Observatory initiative (Grant N. 2011-10-01 from the Alfred P. Sloan Foundation for the project entitled \”Physics and Chemistry of Deep Carbon Bearing Fluids and Minerals\”), and the Agence Nationale de la Recherche (Contract ANR-09-BLAN-0018-01). One of us, M. S., thanks the Region Languedoc-Roussillon for having supported his research at the Universite de Nimes in 2010 and 2011 as an Invited Professor.
KeyWords: carbon dioxide; material science;
DOI: 10.1073/pnas.1118791109

Citations: 50
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