Yoshimura, YukihiroStewart Mukhopadhyay, SarahSomayazulu, MadduryMao, Ho-kwangHemley, Russell J.2011-02-182005Yoshimura, Yukihiro, Sarah T. Stewart, Maddury Somayazulu, Ho-kwang Mao, and Russell J. Hemley. 2006. High-pressure x-ray diffraction and Raman spectroscopy of ice VIII. Journal of Chemical Physics 124(2): 024502.0021-9606http://nrs.harvard.edu/urn-3:HUL.InstRepos:4727478In situ high-pressure/low-temperature synchrotron x-ray diffraction and optical Raman spectroscopy were used to examine the structural properties, equation of state, and vibrational dynamics of ice VIII. The x-ray measurements show that the pressure-volume relations remain smooth up to 23 GPa at 80 K. Although there is no evidence for structural changes to at least 14 GPa, the unit-cell axial ratio c/a undergoes changes at 10-14 GPa. Raman measurements carried out at 80 K show that the nu(Tz)A(1g)+nu Tx,yEg lattice modes for the Raman spectra of ice VIII in the lower-frequency regions (50-800 cm(-1)) disappear at around 10 GPa, and then a new peak of similar to 150 cm(-1) appears at 14 GPa. The combined data provide evidence for a transition beginning near 10 GPa. The results are consistent with recent synchrotron far-IR measurements and theoretical calculations. The decompressed phase recovered at ambient pressure transforms to low-density amorphous ice when heated to similar to 125 K.en-USJournal Article2011-02-1810.1063/1.2140277