Spin crossover equation of state and sound velocities of (Mg0.65Fe0.35)O ferropericlase to 140 GPa

We have determined the elastic and vibrational properties of periclase‐structured (Mg0.65Fe0.35)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 diam...

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Bibliographic Details
Published in:Journal of Geophysical Research: Solid Earth 2012-08, Vol.117 (B8), p.n/a
Main Authors: Chen, Bin, Jackson, Jennifer M., Sturhahn, Wolfgang, Zhang, Dongzhou, Zhao, Jiyong, Wicks, June K., Murphy, Caitlin A.
Format: Article
Language:English
Subjects:
Earth sciences
Earth, ocean, space
equation of state
Exact sciences and technology
ferropericlase
lower mantle
sound velocities
spin transition
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Summary:We have determined the elastic and vibrational properties of periclase‐structured (Mg0.65Fe0.35)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 within situXRD 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 fullP‐Vdata set, resulting in a zero‐pressure volumeV0 = 77.24 ± 0.17 Å3, bulk modulus K0= 159 ± 8 GPa and its pressure‐derivativeK′0= 4.12 ± 0.42 for high‐spin FP35 andK0,LS = 72.9 ± 1.3 Å3, K0,LS = 182 ± 17 GPa with K′0,LSfixed 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 (VS) and compressional (VP) 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 VP and VS, while elevating their ratio (VP/VS). Small amounts (
ISSN:0148-0227
2156-2202
DOI:10.1029/2012JB009162