HR: 1340h
AN: MR23A-0182 [Abstracts]
TI: Synthesis of post-perovskite phase from a natural orthopyroxene
AU: * Shieh, S R
EM: sshieh@mail.ncku.edu.tw
AF: Dept. of Earth Sciences, Nat'l Cheng Kung Univ., Tainan, 701
Taiwan
AU: Duffy, T S
EM: duffy@princeton.edu
AF: Geosciences, Princeton Univ., Princeton, NJ 08544
United States
AU: Kubo, A
EM: akubo@princeton.edu
AF: Geosciences, Princeton Univ., Princeton, NJ 08544
United States
AU: Shen, G
EM: shen@cars.uchicago.edu)
AF: GSECARS, Univ. of Chicago, Chicago, IL 60637
United States
AU: Prakapenka, V B
EM: prakapenka@cars.uchicago.edu
AF: GSECARS, Univ. of Chicago, Chicago, IL 60637
United States
AB:
The existence of a post-perovskite phase in the end-member composition, MgSiO$_{3}$ has been reported at 125 GPa and 2500 K
(Murakami et al., 2004). This has attracted much attention due to its potential relevance for the D$"$ layer at the base of
the mantle. To assess the role that the post-perovskite phase may play in D$"$, the chemical and physical properties of this
new discovered phase need to be investigated in great detail.
In this study, a natural Fe-containing pyroxene sample was used as a starting material. The sample was confirmed to be pure
pyroxene with a=18.2439$\rm{\AA}$, b=8.8368$\rm{\AA}$, c=5.1864$\rm{\AA}$. The powder sample was mixed with 10wt% of Pt
that serves as a pressure standard. Argon was used both to insulate the sample from the diamonds, and to provide a
quasi-hydrostatic environment. In-situ x-ray diffraction experiments were performed at 13-ID-D, GSECARS, Advanced Photon
Source. A monochromatic beam ($\lambda$=0.3344$\rm{\AA}$) was focused to a beam size on the sample of 5x6$\mu$m. The
in-situ x-ray diffraction patterns were collected using an imaging plate. The double-sided laser heating technique was
applied in this study. The temperatures were measured in the range of 1700-1880 K.
The pyroxene sample was compressed to 106 GPa and then heated. Prior to heating, only few very weak pyroxene lines were
observed from the sample. After heating at 1700-1880 K for 36 mins, the post-perovskite phase was observed. The
post-heating pressure was 100 GPa. The synthesis pressure for this sample is significantly lower than previously reported
for end-member MgSiO$_{3}$ (Murakami et al., 2004; Oganov and Ono, 2004; Shim et al., 2004). The unit cell parameters for
the post-perovskite phase at 106(1) GPa and 300 K are a =2.47(2)$\rm{\AA}$, b=8.22(9)$\rm{\AA}$, c=6.12(2)$\rm{\AA}$. The
post-perovskite phase was found to coexist with the perovskite phase in our study. We also find that this post-perovskite
phase can be quenched to ambient conditions, although there is some deterioration in the quality of the diffraction pattern.
The unit cell for this post-perovskite phase at ambient conditions is a =2.57(8)$\rm{\AA}$, b=9.0(3)$\rm{\AA}$,
c=6.8(2)$\rm{\AA}$.
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting