HR: 0800h
AN: MR31B-0373    [Abstracts]
TI: High-Pressure Stability and Equations of State in the Fe-P System: Implications for Iron Meteorites and Planetary Cores
AU: * Scott, H P
EM: hpscott@iusb.edu
AF: Indiana University South Bend, Department of Physics and Astronomy, South Bend, IN 46634, United States
AU: Boateng, N
EM: boatosei@yahoo.com
AF: Indiana University South Bend, Department of Physics and Astronomy, South Bend, IN 46634, United States
AU: Frank, M R
EM: T60MRF1@wpo.cso.niu.edu
AF: Northern Illinois University, Department of Geology and Environmental Geosciences, DeKalb, IL 60115, United States
AU: Meng, Y
EM: ymeng@hpcat.aps.anl.gov
AF: High-Pressure Collaborative Access Team, Carnegie Institution of Washington, Argonne National Laboratory, Argonne, IL 60439, United States
AB: The density, elasticity and structural stability of iron and iron alloys are areas of long-standing interest in planetary science due to the known ubiquity of iron-rich cores in planetary bodies, and the observation that Earth's core is ~10% less dense than pure iron. Furthermore, iron-nickel meteorites often contain inclusions of iron carbide, sulfide and phosphide minerals, which has led to considerable interest in C, S and P (as well as many others) as potential "light" constituents of planetary cores.
As part of our ongoing investigation of Fe₃P, known as schreibersite when found in iron meteorites, we have measured the room-temperature bulk modulus (K_0T) of Fe₂P to 8 GPa using synchrotron X-ray diffraction coupled with Diamond Anvil Cells. Our motivation is to investigate systematics in the Fe-P system due to our previous observation that Fe₃P is not stable above ~15 GPa (Scott et al., 2007). We used the same mixed-phase starting material (both Fe₃P and Fe₂P) as in our previous Fe₃P Equation of State (EoS) study, but examined the bulk sample rather than a selection of pure Fe₃P grains. Accordingly, our data contain information from both phases; we used diffraction peaks from Fe₃P and its EoS to calibrate measurements on Fe₂P relative to Fe₃P. We imposed a constant \frac{c}{a} ratio on this hexagonal structure based on ambient-pressure measurements to reduce fitting parameters, which is consistent with observations of tetragonal Fe₃P over this pressure range. A second order fit (i.e., dK/dP fixed at 4) to the Birch Murnaghan EoS produces a K_0T of 140 ± 4 GPa. This value is 12% lower than that of Fe₃P, and will be used to assess elasticity systematics in iron phosphide phases and potentially other A_xY systems as well.
DE: 1015 Composition of the core
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 6240 Meteorites and tektites (1028, 3662)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting