HR: 1340h
AN: MR23A-0181    [Abstracts]
TI: Synthesis and equation of state of MgGeO$_3$ post-perovskite phase
AU: Kubo, A
EM: akubo@Princeton.EDU
AF: Dept. of Geosci., Princeton Univ., Guyot Hall, Princeton, NJ 08544 United States
AU: * Duffy, T S
EM: duffy@Princeton.EDU
AF: Dept. of Geosci., Princeton Univ., Guyot Hall, Princeton, NJ 08544 United States
AU: Shieh, S R
EM: sshieh@mail.ncku.edu.tw
AF: Dept. of Earth Sci., National Cheng Kung Univ., 1 Univ. Rd., Tainan, 701 Taiwan
AU: Kiefer, B
EM: bkiefer@nmsu.edu
AF: Phys. Dept., New Mexico State Univ., 153 Gardiner Hall, Las Cruces, NM 88003 United States
AU: Prakapenka, V B
EM: prakapenka@cars.uchicago.edu
AF: GSECARS, Univ. of Chicago, Argonne National Lab., Building 434, 9700 South Cass Ave., Argonne, IL 60439 United States
AU: Shen, G
EM: shen@cars.uchicago.edu
AF: GSECARS, Univ. of Chicago, Argonne National Lab., Building 434, 9700 South Cass Ave., Argonne, IL 60439 United States
AB: After the discovery of MgSiO$_3$ post-perovskite (PPv) phase (Murakami et al., 2004), both theoretical and experimental works related to stability and elasticity of MgSiO$_3$ PPv phase have been reported (Oganov and Ono, 2004; Iitaka et al., 2004; Tsuchiya et al., 2004, Shim et al., 2004). However, due to extreme conditions needed to synthesize MgSiO$_3$ PPv phase (125 GPa, 2500 K), it is difficult to experimentally determine various physical properties, such as elasticity, of the PPv phase. Therefore, study of analogue materials could be very useful to examine the structure and physical properties of PPv phases. A good candidate is MgGeO$_3$ because the perovskite form has been synthesized at 12-14 GPa (Leinenweber et al., 1994). MgGeO$_3$ orthopyroxene mixed with 20 wt% Pt was used as a starting material. Ar or NaCl was used as a pressure medium. High-P/T in situ X-ray diffraction experiments in a diamond cell were performed at GSECARS, Argonne National Lab, using an area detector and YLF laser for double-sided heating. In both of our two runs, the PPv phase was synthesized by heating up to 1700K at 80 GPa. The phase was heated at higher pressure and compressed up to 106 GPa, but no further phase transition was observed. In the decompression process, volume data for the phase were taken down to 7 GPa, where the PPv phase was still observed. However, the phase recovered at ambient conditions was neither PPv phase, nor any known polymorph of MgGeO$_3$. By fitting the volume data using Birch-Murnaghan equation of state, both bulk modulus and zero-pressure volume of the PPv phase were determined to be 185 (10) GPa and 184.3 (1.7) $\rm{\AA^3}$, respectively. While c/a ratio is almost constant (2.48) between 6 and 106 GPa, b/a decreases from 3.32 to 3.23 between 6 and 60 GPa, and then remains constant up to 106 GPa. If we use the volume data only between 60 and 106 GPa, both bulk modulus and zero-pressure volume are calculated to be 260 (15) GPa and 174.2 (2.6) $\rm{\AA^3}$, respectively.
DE: 3620 Crystal chemistry
DE: 3630 Experimental mineralogy and petrology
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 1212 Earth's interior--composition and state (8105)
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting