Phase relationships of the system Fe-Ni-S and structure of the high-pressure phase of (Fe1−xNix)3S2

Satoru Urakawa, Ryota Kamuro, Akio Suzuki, Takumi Kikegawa

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3 Citations (Scopus)


The phase relationships of the Fe-Ni-S system at 15 GPa were studied by high pressure quench experiments. The stability fields of (Fe,Ni)3S and (Fe,Ni)3S2 and the melting relationships of the Fe-Ni-S system were determined as a function of Ni content. The (Fe,Ni)3S solid solution is stable in the composition of Ni/(Fe + Ni) > 0.7 and melts incongruently into an Fe-Ni alloy + liquid. The (Fe,Ni)3S2 makes a complete solid solution and melts incongruently into (Fe,Ni)S + liquid, whose structure was determined to show Cmcm-orthorhombic symmetry by in situ synchrotron X-ray diffraction experiments. The eutectic contains about 30 at.% of S, and its temperature decreases with increasing Ni content with a rate of ∼5 K/at.% from 1175 K. The density of the Fe-FeS eutectic composition (Fe70S30) liquid is evaluated to be 6.93 ± 0.08 g/cm3 at 15 GPa and 1200 K based on the Clausius-Clapeyron relations and densities of subsolidus phases. The Fe-Ni-S liquids are a primary sulfur-bearing phase in the deep mantle with a reducing condition (250–660 km depth), and they would play a significant role in the carbon cycle as a carbon host as well as in the generation of diamond.

Original languageEnglish
Pages (from-to)30-37
Number of pages8
JournalPhysics of the Earth and Planetary Interiors
Publication statusPublished - Apr 2018


  • Deep carbon cycle
  • Density of Fe-S liquid
  • FeS
  • High pressure
  • Iron
  • Sulfur

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science


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