HR: 0800h
AN: T21C-0501    [Abstracts]
TI: Ab inito calculations on the properties of CaSiO3 perovskite at high pressure and high temperature
AU: * Li, L
EM: lilli@ic.sunysb.edu
AF: Dept of Geosciences, Stony Brook University, Stony Brook, NY 11794 United States
AU: Weidner, D J
EM: dweidner@sunysb.edu
AF: Dept of Geosciences, Stony Brook University, Stony Brook, NY 11794 United States
AU: Brodholt, J
EM: J.brodholt@ucl.ac.uk
AF: Department of Earth Sciences, University College London, Gower Street, UK, London, WC1E6BT United Kingdom
AU: Alf, D
EM: d.alfe@ucl.ac.uk
AF: Department of Earth Sciences, University College London, Gower Street, UK, London, WC1E6BT United Kingdom
AU: Price, D
EM: d.price@ucl.ac.uk
AF: Department of Earth Sciences, University College London, Gower Street, UK, London, WC1E6BT United Kingdom
AU: Caracas, R
EM: r.caracs@umn.edu
AF: Department of Chemical Engineering and Material Science, Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, MN, 55455 United States
AU: Wentzcovitch, R
EM: r.wentzcovitch@umn.edu
AF: Department of Chemical Engineering and Material Science, Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, MN, 55455 United States
AB: We report the dynamics of the structure and elastic properties of CaSiO3 perovskite from ab initio molecular dynamics (AIMD) calculations at high pressure (P up to 130 GPa) and high temperature (T up to 5000K). Our calculations indicate three separate stability fields: metrically orthorhombic, tetragonal and cubic, with the tetragonal phase dominating the pressure and temperature region between room temperature and 4000K. The cubic phase is not entirely stabilized even at temperatures of the Earth's lower mantle. Calculated X-ray diffraction patterns indicate small super-lattice reflections that could result from the octahedral rotations throughout the P-T region investigated. The calculated elastic constants and velocities are independent of temperature at constant volume. Referenced to room pressure and 2000K, we find: Gr–neisen parameter is r(V) = r0(V/V0)q with r0 = 1.53 and q = 1.02(5), and the Anderson Gruneisen parameter is given by (a/ a0) = (V/V0)dT in which a0 = 2.89 x 10-5 K-1 and dT = 4.09(5). Using the third order Birch Murnaghan equation of state to fit our data, we have for ambient P and T, K0 = 236.6(8) GPa, K0 = 3.99(3), and V0 = 729.0(6) Ǻ3. Calculated acoustic velocities show the following P-T dependence: (dlnVP/ dV)T or P = -1.9 x 10-3; (dlnVS/ dV)T or P = -1.5x 10-3; (dlnVK/ dV)T or P = -2.4 x 10-3; (dlnVs/ dlnVP)T or P = 0.79; (dlnVs/ dlnVK)T or P = 0.63, indicating that the variations in bulk modulus overpower the variations in shear modulus. The bulk modulus of CaSiO3 perovskite is up to 10 per cent lower than MgSiO3 perovskite under lower mantle conditions. The difference diminishes with pressure and temperature. The shear modulus of CaSiO3 perovskite is almost 25 per cent lower compared with MgSiO3 perovskite for shallow lower mantle pressures and temperatures and about 3 per cent lower at the base of the lower mantle. The difference in density of these two perovskite is about 3-4 per cent for all conditions. Both the density and bulk modulus differ from PREM by less than 2 per cent throughout the lower mantle. The shear modulus is ~10 per cent lower at shallow depths grading to ~ 5 per cent by the core-mantle boundary. Thus the seismic velocity of CaSiO3 perovskite will be lower (0 - 6 per cent) than PREM. While we find that the elastic moduli are not appreciably softened, the attenuation due to the ferroelastic character of CaSiO3 perovskite may make this phase very distinctive in its seismic signature.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
SC: Tectonophysics [T]
MN: Fall Meeting 2005