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Spin crossover equation of state and sound velocities of (Mg_(0.65)Fe_(0.35))O ferropericlase to 140 GPa

Chen, Bin and Jackson, Jennifer M. and Sturhahn, Wolfgang and Zhang, Dongzhou and Zhao, Jiyong and Wicks, June K. and Murphy, Caitlin A. (2012) Spin crossover equation of state and sound velocities of (Mg_(0.65)Fe_(0.35))O ferropericlase to 140 GPa. Journal of Geophysical Research B, 117 . Art. No. B08208. ISSN 0148-0227. doi:10.1029/2012JB009162.

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We have determined the elastic and vibrational properties of periclase-structured (Mg_(0.65)Fe_(0.35))O (“FP35”), a composition representative of deep mantle “pyrolite” or chondrite-pyroxenite models, from nuclear resonant inelastic x-ray scattering (NRIXS) and x-ray diffraction (XRD) measurements in diamond-anvil cells at 300 K. Combining with in situ XRD measurements, the Debye sound velocity of FP35 was determined from the low-energy region of the partial phonon density of states (DOS) obtained from NRIXS measurements in the pressure range of 70 to 140 GPa. In order to obtain an accurate description of the equation of state (EOS) for FP35, separate XRD measurements were performed up to 126 GPa at 300 K. A new spin crossover EOS was introduced and applied to the full P-V data set, resulting in a zero-pressure volume V_0 = 77.24 ± 0.17 Å^3, bulk modulus K_0 = 159 ± 8 GPa and its pressure-derivative K′_0 = 4.12 ± 0.42 for high-spin FP35 and K_(0,LS) = 72.9 ± 1.3 Å^3, K_(0,LS) = 182 ± 17 GPa with K′_(0,LS) fixed to 4 for low-spin FP35. The high-spin to low-spin transition occurs at 64 ± 3 GPa. Using the spin crossover EOS and Debye sound velocity, we derived the shear (V_S) and compressional (V_P) velocities for FP35. Comparing our data with previous results on (Mg,Fe)O at similar pressures, we find that the addition of iron decreases both V_P and V_S, while elevating their ratio (V_P/V_S). Small amounts (<10%) of low-spin FP35 mixed with silicates could explain moderate reductions in wave speeds near the core mantle boundary (CMB), while a larger amount of FP35 near the CMB would not allow a large structure to maintain neutral buoyancy.

Item Type:Article
Related URLs:
URLURL TypeDescription
Jackson, Jennifer M.0000-0002-8256-6336
Sturhahn, Wolfgang0000-0002-9606-4740
Zhang, Dongzhou0000-0002-6679-892X
Zhao, Jiyong0000-0002-0777-3626
Additional Information:© 2012 American Geophysical Union. Received 21 January 2012; revised 6 July 2012; accepted 13 July 2012; published 30 August 2012. We thank J. Yan for help with the experimental set-up at the ALS and D. J. Bower for helpful discussions. The authors are grateful to NSF-EAR-CAREER-0956166, the Texaco postdoctoral fellowship from Caltech (to B.C.), and Keck Institute for Space Studies for support of this work. Sector 3 operations, beamline 12.2.2 and the gas-loading facility are partially supported by COMPRES. Use of the Advanced Photon Source is supported by the U.S. DOE, Office of Science (DE-AC02-06CH11357). The Advanced Light Source is supported by the U.S. DOE, Office of Science (DE-AC02-05CH11231). Microprobe analyses were carried out at the Caltech GPS Division Analytical Facility (funded in part by the MRSEC Program of the NSF under DMR-0080065). We also thank two anonymous reviewers and the editors for their useful comments.
Group:Keck Institute for Space Studies, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Texaco Postdoctoral FellowshipUNSPECIFIED
Keck Institute for Space Studies (KISS)UNSPECIFIED
Department of Energy (DOE)DE-AC02-06CH11357
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:equation of state; ferropericlase; lower mantle; sound velocities; spin transition
Record Number:CaltechAUTHORS:20121108-093107958
Persistent URL:
Official Citation: Chen, B., J. M. Jackson, W. Sturhahn, D. Zhang, J. Zhao, J. K. Wicks, and C. A. Murphy (2012), Spin crossover equation of state and sound velocities of (Mg0.65Fe0.35)O ferropericlase to 140 GPa, J. Geophys. Res., 117, B08208, doi:10.1029/2012JB009162.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35351
Deposited By: Ruth Sustaita
Deposited On:08 Nov 2012 18:06
Last Modified:09 Nov 2021 23:14

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