HR: 0800h
AN: MR31A-0147    [Abstracts]
TI: Vibrational And Elastic Properties Of Delta-AlOOH and Phase D
AU: * Tsuchiya, J
EM: junt@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime, 790-8577, Japan
AU: Tsuchiya, T
EM: takut@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime, 790-8577, Japan
AB: It has been believed that water is transported into the deep mantle by hydrous minerals in subducting cold slabs. Existence of water in deep Earth minerals is known to affect their viscosity, melting temperature, and elastic properties. We have found using first principles techniques that both of δ-AlOOH, and phase D which are relevant to the carrier of water into the lower mantle, change to have the symmetric hydrogen bond at lower mantle pressures. Here we report the effects of hydrogen bond symmetrization on the vibrational properties of δ-AlOOH and phase D. We found that as increasing hydrogen bond strength by compression, the OH stretching frequencies decrease until the hydrogen bond changes to be symmetric. After the symmetrization of the hydrogen bond, the corresponding OH stretching frequencies, in turn, gradually increase with increasing pressure. These softening and subsequent hardening of the OH vibrational modes, which have also been reported in high pressure molecular solid, ice VII and VIII phases at ~60 GPa, occurs in hydrous mineral, δ-AlOOH and phase D, at much lower pressures of ~30 GPa and ~40 GPa, respectively. These vibrational properties can be good indications for experimental detection of the hydrogen bond symmetrization. We also report the elastic properties of δ-AlOOH and phase D and discuss seismic signatures expected to occur associated with the hydrogen bond symmetrization. Research supported in part by JSPS.
DE: 1042 Mineral and crystal chemistry (3620)
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting