HR: 1340h
AN: MR23A-1025    [Abstracts]
TI: High-Pressure Raman Spectroscopy of Protonic Diffusion in ice VII
AU: * Tkachev, S N
EM: stkachev@soest.hawaii.edu
AF: Private Residence, 12053 Cherokee Park Rd., Livermore, CO 80536, United States
AU: Goncharov, A F
EM: goncharov@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., N.W., Washington, DC 20015, United States
AB: Raman spectroscopy studies of mutual diffusion of protons and deuterons in ice VII were carried out at 473 K and pressures up to 25 GPa in a diamond anvil cell (DAC). Despite the fact that the diffusion model proposed for water ices is fifty five years old, the experimental verification of this mechanism remains extremely challenging. Present Raman spectroscopy measurements of two ice layers (H₂O and D₂O, accordingly) loaded without mixing in a gasket-insert assemblage signify another major advancement in experimental investigation of this phenomenon. Previous infrared spectroscopy studies of H₂O/D₂O ice bilayer at high pressure did not take into account variations of pressure in the DAC during the heating cycles, and, thus, might not be that accurate. The use of Raman scattering spectroscopy for measurements of mutual diffusion of protons and deuterons provides us with an opportunity to monitor pressure in situ. Our results show that pressure dependence of diffusion coefficients is negative with activation volume of ~0.001 eV/GPa. On the basis of these estimates a lower boundary of superionic (protonic diffusion coefficient is in the order of 10^-8 m²/s) state of water ice will be presented on the phase diagram of water.
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting