Volume 77, Number 4, February 2007
Article Number 46002
Number of page(s) 5
Section Condensed Matter: Structural, Mechanical and Thermal Properties
Published online 09 February 2007
EPL, 77 (2007) 46002
DOI: 10.1209/0295-5075/77/46002

Molecular carbon dioxide at high pressure and high temperature

V. M. Giordano1, 2 and F. Datchi1

1  Physique des Milieux Denses, IMPMC, CNRS UMR 7590, Université Pierre et Marie Curie-Paris VI, 140 rue de Lourmel, 75015 Paris, France
2  LENS- via N. Carrara 1, Polo Scientifico - 50019 Sesto Fiorentino (FI), Italy

received 25 October 2006; accepted in final form 20 December 2006; published February 2007
published online 9 February 2007

The existence of intermediate states between the molecular and non-molecular forms of carbon dioxide has been actively debated in the recent past. Here we report new experiments at pressures up to 20 GPa and in the temperature range 300$\hbox{--} $950 K. They revealed the presence of a previously unobserved molecular phase, which we identified as the theoretically predicted high-temperature Cmca phase. Its relation and relative stability with respect to the other solid phases are discussed based on spectroscopic and melting data. We show that the existence of this strictly molecular phase challenges the interpretation of phases IV and II as intermediate forms between the molecular and covalent-bonded solids.

62.50.+p - High-pressure and shock wave effects in solids and liquids.
68.18.Jk - Phase transitions.
78.30.-j - Infrared and Raman spectra.

© Europhysics Letters Association 2007