HR: 09:30h
AN: V21A-07    [PDF]
TI: Low $<->$ high density transformations in ice
AU: * Umemoto, K
EM: umemoto@cems.umn.edu
AF: Department of Chemical Engineering and Material Science, University of Minnesota, 421 Washington Ave SE, Minneapolis, MN 55455 United States
AU: Wentcovich, R M
EM: wentzcov@cems.umn.edu
AF: Department of Chemical Engineering and Material Science, University of Minnesota, 421 Washington Ave SE, Minneapolis, MN 55455 United States
AB: We have investigated through first principles computations the pressure induced behavior of ice XI and ice VIII. They are respectively low and high density hydrogen-ordered forms of ice that amorphize under pressure inside each other' stability field. We have found that: 1) low-to-high density transformations between ordered structures consisting of one and two hydrogen-bond-networks should happen continuously and preserve the style of electric dipole ordering. 2) In this process we have synthesized computationally two metastable phases, antiferroelectric ice XI-like and ferroelectric VIII-like. Higher energy barriers for structural transitions involving dipole reordering leads to large metastability fields. 3) Entire acoustic branches destabilize before the low$<->$high density transformations occur. The multitude of metastable structures produced by these intervening instabilities compete and conspire to produce the amorphous. In simple Landau terms, ice XI and VIII are located in deep basins of the free-energy landscape separated from each other by a few intermedieate rugged basins associated with amorphous states.
DE: 3924 High-pressure behavior
DE: 6020 Ice
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting