Elasticity of CaTiO 3 –CaSiO 3 perovskites (original) (raw)
Related papers
Elasticity of CaSiO3 perovskite at high pressure and high temperature
Physics of the Earth and Planetary Interiors, 2006
Ab initio molecular dynamic (AIMD) simulations were performed to calculate the equation of state (EOS) of CaSiO 3 perovskite at mantle pressure-temperature conditions. At temperatures above 2000 K, even though the hydrostatic crystal structure is metrically tetragonal in the pressure range of 13-123 GPa, the symmetry of the elastic moduli is consistent with cubic symmetry. Our results show that elastic constants and velocities are independent of temperature at constant volume. Referenced to room pressure and 2000 K, we find: Grűneisen parameter is γ(V) = γ 0 (V/V 0 ) q with γ 0 = 1.53 and q = 1.02(5), and the Anderson Grűneisen parameter is given by (α/α 0 ) = (V/V 0 ) δ T in which α 0 = 2.89 × 10 −5 K −1 and δ T = 4.09(5). Using the third order Birch Murnaghan equation of state to fit our data, we have for ambient P and T, K 0 = 236.6(8) GPa, K 0 = 3.99(3), and V 0 = 729.0(6)Å 3 . Calculated acoustic velocities show the following P-T dependence: (∂ln V P /∂V) T or P = −1.9 × 10 −3 ; (∂ln V S /∂V) T or P = −1.5 × 10 −3 ; (∂ln V Φ /∂V) T or P = −2.4 × 10 −3 ; (∂ln V S /∂ln V P ) T or P = 0.79; (∂ln V S /∂ln V Φ ) T or P = 0.63, indicating that the variations in bulk modulus overpower the variations in shear modulus.
Article Elastic Properties of CaSiO3 Perovskite from ab initio Molecular Dynamics
2015
Ab initio molecular dynamics simulations were performed to investigate the elasticity of cubic CaSiO 3 perovskite at high pressure and temperature. All three independent elastic constants for cubic CaSiO 3 perovskite, C 11 , C 12 , and C 44 , were calculated from the computation of stress generated by small strains. The elastic constants were used to estimate the moduli and seismic wave velocities at the high pressure and high temperature characteristic of the Earth's interior. The dependence of temperature for sound wave velocities decreased as the pressure increased. There was little difference between the estimated compressional sound wave velocity (V P) in cubic CaSiO 3 perovskite and that in the Earth's mantle, determined by seismological data. By contrast, a significant difference between the estimated shear sound wave velocity (V S) and that in the Earth's mantle was confirmed. The elastic properties of cubic CaSiO 3 perovskite cannot explain the properties of the Earth's lower mantle, indicating that the cubic CaSiO 3 perovskite phase is a minor mineral in the Earth's lower mantle.
Elastic Properties of CaSiO3 Perovskite from ab initio Molecular Dynamics
Entropy, 2013
Ab initio molecular dynamics simulations were performed to investigate the elasticity of cubic CaSiO 3 perovskite at high pressure and temperature. All three independent elastic constants for cubic CaSiO 3 perovskite, C 11 , C 12 , and C 44 , were calculated from the computation of stress generated by small strains. The elastic constants were used to estimate the moduli and seismic wave velocities at the high pressure and high temperature characteristic of the Earth's interior. The dependence of temperature for sound wave velocities decreased as the pressure increased. There was little difference between the estimated compressional sound wave velocity (V P ) in cubic CaSiO 3 perovskite and that in the Earth's mantle, determined by seismological data. By contrast, a significant difference between the estimated shear sound wave velocity (V S ) and that in the Earth's mantle was confirmed. The elastic properties of cubic CaSiO 3 perovskite cannot explain the properties of the Earth's lower mantle, indicating that the cubic CaSiO 3 perovskite phase is a minor mineral in the Earth's lower mantle.
Weak cubic CaSiO3 perovskite in the Earth’s mantle
Nature, 2022
Cubic CaSiO3 perovskite is a major phase in subducted oceanic crust, where it forms at a depth of about 550 km from majoritic garnet 1,2. We measured the plastic strength of cubic CaSiO3 perovskite at pressure and temperature conditions typical for a subducting slab up to a depth of about 1200 km. Contrary to tetragonal CaSiO3 previously investigated at room temperature 3,4 , we find that cubic CaSiO3 perovskite is a comparably weak phase at temperatures of the lower mantle. We find its viscosity to be substantially lower as compared to bridgmanite and ferropericlase, possibly making cubic CaSiO3 perovskite the weakest lower mantle phase. Our findings suggest that cubic CaSiO3 perovskite will govern the dynamics of subducting slabs. It further provides a mechanism to separate subducted oceanic crust from the underlying mantle. Depending on the depth of the separation, basaltic crust could accumulate at the boundary between the upper and lower mantle, where cubic CaSiO3
Ab initio study of the high-pressure behavior of CaSiO3 perovskite
Physics and Chemistry of Minerals, 2005
Using density functional simulations, within the generalized gradient approximation and projectoraugmented wave method, we study structures and energetics of CaSiO 3 perovskite in the pressure range of the Earth's lower mantle (0-150 GPa). At zero Kelvin temperature the cubic ðPm " 3 mÞ CaSiO 3 perovskite structure is unstable in the whole pressure range, at low pressures the orthorhombic (Pnam) structure is preferred. At 14.2 GPa there is a phase transition to the tetragonal (I4/mcm) phase. The CaIrO 3 -type structure is not stable for CaSiO 3 . Our results also rule out the possibility of decomposition into oxides.
Geophysical Research Letters, 2005
1] Brillouin scattering measurements on aluminous magnesium silicate perovskite, arguably the most abundant phase in Earth, have been performed to 45 GPa in a diamond anvil cell at room temperature, using methanol-ethanol-water and neon as pressure transmitting media. The experiments were performed on a polycrystalline sample of aluminous MgSiO 3 perovskite containing 5.1 ± 0.2 wt.% Al 2 O 3 . The pressure derivatives of the adiabatic bulk (K 0S ) and shear (m 0S ) moduli are 3.7 ± 0.3 and 1.7 ± 0.2, respectively. These measurements allow us to evaluate whether the observed lateral variations of seismic wave speeds in Earth's lower mantle are due at least in part to a chemical origin. Our results indicate that a difference in the aluminum content of silicate perovskite, reflecting a variation in overall chemistry, is a plausible candidate for such seismic heterogeneity. Citation: Jackson,
Thermal equation of state of CaSiO3 perovskite
Journal of Geophysical Research, 1996
A comprehensive pressure-volume-temperature data set has been obtained for CaSiO 3 perovskite up to 13 GPa and 1600 K, using synchrotron X ray diffraction with a cubic-anvil, DIA-6 type apparatus (SAM-85). For each volume measurement, nonhydrostatic stress is determined from the relative shift in the diffraction lines of NaC1, within which the sample was embedded. Heating to above 973 K greatly reduced the strength of NaC1 (to below 0.05 GPa), making the measurements hydrostatic. At room temperature the cubic perovskite structure remains metastable at pressures as low as 1 GPa, below which the sample transforms into an amorphous phase as indicated by a large background, a marked decrease in diffraction signals, and an anomalous volume decrease of the remaining crystalline phase. Because our experimental uncertainties are significantly smaller than those in previous measurements, the new data provide a tighter constraint on the zero pressure bulk modulus for CaSiO perovskite. A new set of room temperature equation of state parameters are identified so that both our data and the diamond cell data of Mao et al. [1989] are compatible [Kr0 = 232(8) GPa, K½0 = 4.8(3), and V0 -45.58(4) •3]. Volume measurements along several isotherms under both stable and metastable pressure conditions allow isochoric and isobaric interpolations within the range of experimental pressure and temperature conditions. Analyses using various approaches yielded consistent results for (OKr/OT)e of -0.033(8) GPa K -•, and 7 1 1 (Oa/OP)r of -6.3 X 10-GPa-K-, with a zero-pressure thermal expansion a 0 of 3.0 x 10 -s K -•. The thermal pressure is found to be virtually independent of volume, and thus the Anderson-Grtineisen parameter •r-K¬ = 4.8. These results are used to predict the bulk modulus and density of CaSiO 3 perovskite under lower mantle conditions. Along an adiabat with the foot temperature of 2000 K, the density of the perovskite agrees with that of the preliminary reference Earth model (PREM) within 1% throughout the lower mantle. The bulk modulus shows a smaller pressure dependence along the adiabat; it matches that of PREM at the top of the lower mantle but is about 10% too low near the core-mantle boundary. Paper number 95JB03254, 0148-0227/96/95 J B-03254 $05.00 ZaM and Madon, 1991]. However, these phases were synthesized without the presence of the major lower mantle phases ((Mg,Fe)SiO3 perovskite and magnesiowustite) and therefore their existence in the lower mantle is questionable on petrological grounds. A recent phase equilibrium study using a more representative composition of the mantle (pyrolite) shows that A1 is mostly accommodated in (Mg,Fe)SiO3 perovskite with no separate aluminous phase observed [Irifune, 1994]. On the other hand, a number of other experimental studies indicate that the most likely calcium-bearing phase is CaSiO 3 perovskite [Ringwood and Major, 1971; Liu and Ringwood, 1975, Gasparik, 1989, 1971]. Thus the lower mantle may be composed mainly of aluminous (Mg,Fe)SiO3 perovskite, Ca-SiO 3 perovskite, and magnesiowustite, as well as 1 or 2% of other phases. Equation of state measurements of CaSiO 3 perovskite are complicated by the instability of this material. Thus it is not possible to synthesize the sample in one experiment and conduct high-pressure, high-temperature measurements in another. Rather, the synthesis experiment must be capable of giving equation of state information. Equation of state of Ca-SiO3 perovskite has been measured at ambient temperature by several groups in a diamond anvil cell [e.g., Mao et al., 1989; Tarrida and Richet, 1989; Tamai and Yagi, 1989]. Wang and Weidner [1994] reported the first in situ determination of the 661 662 WANG ET AL.: THERMOELASTICITY OF CASIO 3 PEROVSKITE zirconia fill •'%•,•'•i boron ] ,'ree",SøsXu" l i rain • •; ••boro"nitride • tubPng½carb;n • ] Saheater/, , mple chamber • Pth•aterlead Møcurf antdIsk sam le ;
Ab initio molecular dynamics study of CaSiO3 perovskite at P-T conditions of Earth’s lower mantle
Physical Review B, 2006
First-principles molecular dynamics calculations were performed in order to investigate the structure and properties of what is thought to be the third most abundant phase in the Earth's lower mantle, CaSiO 3 perovskite. The commonly assumed cubic structure was found to be stable at high temperatures ͑T Ͼ 1000-2000 K͒ and unstable at low temperatures at all pressures. For this structure we investigate the thermal equation of state and the Grüneisen parameter. We predict that the ground state of CaSiO 3 perovskite is tetragonal ͑space group I4/mcm͒. At room temperature an orthorhombic structure ͑space group Imma͒ is possible, which explains puzzling experimental X-ray powder diffraction patterns. We consider the structure relation between the Imma and the I4/mcm structures and show that the Imma structure can be obtained by a counterintuitive symmetry-lowering transition on increasing temperature.
Equation of state of CaSiO 3 perovskite to 96 GPa
Geophysical Research Letters, 1989
The CaSiO3 perovskite has been synthesized in a laser-heated diamond-anvil cell at initial pressures ranging from 15 to 85 GPa. Chemical microanalyses of the quenched product show negligible solubility in the CaSiO3 perovskite of aluminum from the ruby added for pressure measurements. The compression of CaSiO3 perovskite has been measured to 96 GPa with X-ray methods. The results do not show a significant deviation of Ko' from 4, and with a Birch-Mumaghan equation of state we obtain a 1-bar molar volume Vo = 45.60 + 0.10 •3 and a bulk modulus Ko = 275 + 15 GPa. This perovskite may be an "invisible" component of the lower mantle in view of the similarity of its density with that given by the standard Earth model, PREM. Finch, Elastic properties from acoustic and volume compression experiments, Phys. Earth Planet. Inter., 25, 140-158, 1981. Chopelas, A.Thermal expansion, heat capacity, and phase changes of forsteritc at mantle pressures: comparison to MgO, Phys. Chem. Minerals. In press, 1989. Dziewonski, A.M. and D. L. Anderson, Preliminary reference earth model, Phys. Earth Planet. Inter., 25, 297-356, 1981.