HR: 0830h
AN: V11D-0520    [PDF]
TI: First-principles Study Of Hydrous Minerals, $\delta$-AlOOH And Phase D (= G) Under High Pressure
AU: * Tsuchiya, J
EM: junt@cems.umn.edu
AF: Department of Chemical Engineering and Materials Science, Institute of Technology, University of Minnesota, 421 Washington Avenue S. E., Minneapolis, MN 55455 United States
AU: * Tsuchiya, J
EM: junt@cems.umn.edu
AF: Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Tsuchiya, T
EM: takut@cems.umn.edu
AF: Department of Chemical Engineering and Materials Science, Institute of Technology, University of Minnesota, 421 Washington Avenue S. E., Minneapolis, MN 55455 United States
AU: Tsuneyuki, S
EM: stsune@cms.phys.s.u-tokyo.ac.jp
AF: Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AB: The existence of water in the earth is paid attention because it is thought that the presence of water affects the physical properties of earth constituent minerals. We report the physical property and crystal structure of $\delta$-AlOOH and phase D under high pressure. $\delta$-AlOOH is a new high pressure phase of boemite and diaspore and phase D is a highest pressure phase of dense hydrous magnesium silicate (DHMS). These phases are important as a possible water reservoir in the subducting slab and as a potentially water supplier into the Earth's lower mantle. While many experiments have been carried out for the quest of stable hydrous and nominal anhydrous minerals in earth's interior, its particular states of hydrogen or hydrogen bond in these minerals under high pressure have not been well clarified. In order to investigate pressure effects on structure of these hydrous minerals and its nature of hydrogen bond, we conducted first-principles theoretical calculation in which implemented Troullier-Martins pseudopotential and plane wave basis sets. Throughout the calculation in this study, we used GGA-PBE for exchange correlation functional. We found that the hydrogen bonds of both phases have symmetric character under high pressure about 30 GPa. We report structures, bulk moduli and O-H stretching frequencies of $\delta$-AlOOH and phase D relevant to asymmetric and symmetric hydrogen bond. The bulk modulus of symmetric hydrogen bond phase of $\delta$-AlOOH is more than 20% harder than that of asymmetric one. The subtle change of hydrogen position with pressure causes remarkable alteration of hydrogen bond strength and thus significantly changes bulk properties and compression behavior.
DE: 3900 MINERAL PHYSICS
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting