Sound velocity of hexagonal close-packed iron up to core pressures

Eiji Ohtani, Yuki Shibazaki, Takeshi Sakai, Kenji Mibe, Hiroshi Fukui, Seiji Kamada, Tatsuya Sakamaki, Yusuke Seto, Satoshi Tsutsui, Alfred Q.R. Baron

Research output: Contribution to journalArticlepeer-review

44 Citations (Scopus)


We determined the compressional velocity of hcp-Fe using high-resolution inelastic X-ray scattering combined with in situ X-ray powder diffraction: Our measurements extend up to 174 GPa at room temperature, to 88 GPa at 700 K, and to 61.5 GPa at 1000 K. Our data, including those obtained at high temperature, are well described by a linear relation to density, extending the range of verification of Birch's law and suggesting only small temperature dependence up to 1000 K. This result, once compared to the preliminary reference Earth model seismologically based model, indicates that there is either a strong temperature effect on Birch's law above 1000 K or the composition of the core is rather different than expected, containing, e.g., heavy impurities. Noting that both recent theoretical calculations and shock wave velocity measurements are consistent with modification of Birch's law at high temperature, we favor the former explanation. Key Points We measured the velocity of hcp-Fe to 174 GPa and 300 K by IXS We confirmed no temperature dependence on Birch's law to 60 GPa and 1000 K We argued the light elements in the inner core based on the present study

Original languageEnglish
Pages (from-to)5089-5094
Number of pages6
JournalGeophysical Research Letters
Issue number19
Publication statusPublished - 2013 Oct 16


  • hcp-iron
  • high pressure
  • inelastic X-ray scattering
  • inner core
  • sound velocity


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