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Six-fold coordinated carbon dioxide VI
Lawrence Livermore National Laboratory.
(Lawrence Livermore National Laboratory)
Lawrence Livermore National Laboratory.
Stockholm University, Faculty of Science, Department of Physics.
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2007 (English)In: Nature Materials, ISSN 1476-1122, Vol. 6, 34-38 p.Article in journal (Refereed) Published
Abstract [en]

Under standard conditions, carbon dioxide (CO2) is a simple molecular gas and an important atmospheric constituent, whereas silicon dioxide (SiO2) is a covalent solid, and one of the fundamental minerals of the planet. The remarkable dissimilarity between these two group IV oxides is diminished at higher pressures and temperatures as CO2 transforms to a series of solid phases, from simple molecular to a fully covalent extended-solid V, structurally analogous to SiO2 tridymite. Here, we present the discovery of an extended-solid phase of CO2: a six-fold coordinated stishovite-like phase VI, obtained by isothermal compression of associated CO2-II (refs 1,2) above 50 GPa at 530–650 K. Together with the previously reported CO2-V (refs 3–5) and a-carbonia6, this extended phase indicates a fundamental similarity between CO2 (a prototypical molecular solid) and SiO2 (one of Earth's fundamental building blocks). We present a phase diagram with a limited stability domain for molecular CO2-I, and suggest that the conversion to extended-network solids above 40–50 GPa occurs via intermediate phases II (refs 1,2), III (refs 7,8) and IV (refs 9,10). The crystal structure of phase VI suggests strong disorder along the c axis in stishovite-like P42/mnm, with carbon atoms manifesting an average six-fold coordination within the framework of sp3 hybridization.

Place, publisher, year, edition, pages
2007. Vol. 6, 34-38 p.
National Category
Condensed Matter Physics Condensed Matter Physics
Research subject
Materials Science
URN: urn:nbn:se:su:diva-27409DOI: 10.1038/nmat1800OAI: diva2:214094
Available from: 2009-05-02 Created: 2009-05-02 Last updated: 2009-05-05Bibliographically approved
In thesis
1. Experimental investigation of molecular solids and vanadium at high pressure and temperature
Open this publication in new window or tab >>Experimental investigation of molecular solids and vanadium at high pressure and temperature
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding high pressure effects on simple molecular system is of great interest for condensed matter science and geophysics. Accessing the static pressure and temperature regions found in planetary interiors is made possible by the development of the Diamond Anvil Cell technique. We developed a double sided resistive heating method for the membrane DAC operating in low pressure (<0.5 mTorr) pressure environment requiring only 175 W input power to reach sample temperatures up to 1300 K. We applied this technique successfully to study molecular solids at high temperatures, such as H2, N2 and CO2. We made an attempt to determine the melting line of hydrogen and present data up to 26 GPa in agreement with literature. Raman spectroscopy of Nitrogen indicates a high stability of the ε molecular phase, while θ phase is only accessible via certain P, T paths. Studies of solid CO2 at high pressure and temperature lead to the discovery of a six-fold coordinated stishovite-like phase VI, obtained by isothermal compression of associated CO2-II above 50 GPa at 530-650 K, or by isobaric heating of CO2-III above 55 GPa. From our X-ray diffraction experiment on isothermally compressed H2O we report a coexistence of ice VII and symmetric ice X from the start of the transition pressure 40GPa to just below 100 GPa and a volume change of 4% across the transition.

Vanadium, a transition metal undergoes a phase transition upon compression unlike other elements (Nb, Ta) from its group. We confirm the bcc phase transition to rhombohedral structure at 62 GPa under quasi hydrostatic compression in Ne pressure medium. Compression without pressure medium results in a much lower 30 GPa transition pressure at room temperature and 37 GPa at 425 K, pointing to a positive phase line between the bcc and rhombohedral crystalline phases.


Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2009. 71 p.
molecular solid, high pressure, vanadium, phase transition
National Category
Physical Sciences
Research subject
Physics Of Matter
urn:nbn:se:su:diva-26917 (URN)978-91-7155-868-8 (ISBN)
Public defence
2009-05-26, sal FB53, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Available from: 2009-05-05 Created: 2009-04-17 Last updated: 2009-05-04Bibliographically approved

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