Equation of state of the postperovskite phase synthesized from a natural (Mg,Fe)SiO3 orthopyroxene

Sean R. Shieh, Thomas S. Duffy, Atsushi Kubo, Guoyin Shen, Vitali B. Prakapenka, Nagayoshi Sata, Kei Hirose, Yasuo Ohishi

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Using the laser-heated diamond anvil cell, we investigate the stability and equation of state of the postperovskite (ppv, CalrO3-type) phase synthesized from a natural pyroxene composition with 9 mol.% FeSiO3. Our measured pressure-volume data from 12-106 GPa for the ppv phase yield a bulk modulus of 219(5) GPa and a zero-pressure volume of 164.9(6) Å3 when K′0 = 4. The bulk modulus of ppv is 575(15) GPa at a pressure of 100 GPa. The transition pressure is lowered by the presence of Fe. Our x-ray diffraction data indicate the ppv phase can be formed at P > 109(4) GPa and 2,400(400) K, corresponding to ≈400-550 km above the core-mantle boundary. Direct comparison of volumes of coexisting perovskite and CalrO3-type phases at 80-106 GPa demonstrates that the ppv phase has a smaller volume than perovskite by 1.1(2)%. Using measured volumes together with the bulk modulus calculated from equation of state fits, we find that the bulk sound velocity decreases by 2.3(2.1)% across this transition at 120 GPa. Upon decompression without further heating, it was found that the ppv phase could still be observed at pressures as low at 12 GPa, and evidence for at least partial persistence to ambient conditions is also reported.

Original languageEnglish (US)
Pages (from-to)3039-3043
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number9
StatePublished - Feb 28 2006

All Science Journal Classification (ASJC) codes

  • General


  • Diamond anvil cell
  • High pressure
  • Lower mantle
  • Phase transition
  • X-ray diffraction


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