HR: 1340h
AN: MR43C-1524    [Abstracts]
TI: Structure transition of post-spinels, CaTi2O4, CaMn2O4 and CaFe2O4 under high pressures up to 75GPa
AU: Yamanaka, T
EM: t.yamanaka@kce.biglobe.ne.jp
AF: Carnegie Institute of Washington Geophysical Laboratory, 5231 Broard Branch Roard NW, Washington DC, DC 20015,
AU: Yamanaka, T
EM: t.yamanaka@kce.biglobe.ne.jp
AF: Department of Earth and Space Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan
AU: Yamanaka, T
EM: t.yamanaka@kce.biglobe.ne.jp
AF: Center of Quantum Science and Technology, Osaka University, 1-3 Machikaneyama, Toyonaka, 560-0043, Japan
AU: Uchida, A
EM: Uchida@ess.sci.osaka-u.ac.jp
AF: Department of Earth and Space Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan
AU: * Nakamoto, Y
AF: Center of Quantum Science and Technology, Osaka University, 1-3 Machikaneyama, Toyonaka, 560-0043, Japan
AB: Three structures of CaMn2O4, CaTi2O4 and CaFe2O4 have been proposed as post-spinels phases. Since these structures are very similar, the several arguments or confusions appear in the high-pressure studies, leading many problems that are yet to be solved. Systematic powder diffraction studies related to these three phases were executed under high pressure using synchrotron radiation. Three samples have further high-pressure polymorphs. CaMn2O4 transforms to CaTi2O4 type structure at about 30 GPa. The MnO6 octahedron in the former structure is distorted by the Jahn-Teller effect due to Mn3+ in the octahedral site. This transition probably is induced by the high-low spin transition, because the low spin configuration is very similar to that of Ti3+ in the octahedral site of CaTi2O4. A new phase was observed at pressures over 50 GPa during compression of CaFe2O4. Analysis of this structure was been performed by Monte Carlo method after indexing to find possible structure candidates and then Rietveld profile fitting was applied using the initial models taken from the candidates. This structure, with space group of Pnam, is produced via martensic transformation by displacing atoms in every three layer perpendicular to the c axis. CaTi2O4 also has a new high-pressure polymorph over 39 GPa. The structure has a space group of Bbnm estimated from the indexing. The most provable post-spinel candidate in the mantle is the CaTi2O4 type structure. The CaMn2O4 type structure is only formed at high pressure from spinel phases with atoms susceptible to Jahn
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3630 Experimental mineralogy and petrology
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting