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K. Aoki, H. Yamawaki, M. Sakashita, Y. Gotoh, and K. Takemura
[Science, Vol.263, pp.356-358, 1994]
Powder diffraction study using synchrotron x-ray source and an image-plate detector has shown that the cubic Pa3 structure commonly called "dry ice" transforms to an orthorhombic Cmca structure at about 10 GPa at room temperature. The unit cell determined at 11.8 GPa has the dimension of a=0.4330 nm, b=0.4657 nm, and c=0.5963 nm, containing four molecules. Molecules are located at the base centered positions with the molecular axes inclined at about 52 degrees with respect to the crystallographic c-axis. The volume change associated with the cubic-orthorhombic transition was found to be less than 0.2%.