In situ X-ray diffraction measurements of the <Emphasis Type="Italic">fcc</Emphasis>–<Emphasis Type="Italic">hcp</Emphasis> phase transition boundary of an Fe–Ni alloy in an internally heated diamond anvil cell |
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| Authors: | Email author" target="_blank">Tetsuya?KomabayashiEmail author Kei?Hirose Yasuo?Ohishi |
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| Institution: | (1) Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro Tokyo, 152-8551, Japan;(2) Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka Kanagawa, 237-0061, Japan;(3) Japan Synchrotron Radiation Research Institute, Sayo Hyogo, 679-5198, Japan |
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| Abstract: | The phase transition boundary between the face-centered cubic (fcc) structure and hexagonal close-packed (hcp) structure in an Fe–Ni alloy was determined at pressures from 25 to 107 GPa by using an internally resistive-heated diamond
anvil cell (DAC), combined with in situ synchrotron X-ray diffraction measurements. The fcc–hcp phase transition boundary in Fe–9.7 wt% Ni is located at slightly lower temperatures than that in pure Fe, confirming the
previous understanding that the addition of Ni expands the stability field of the fcc phase. The dP/dT slope of the boundary was determined to be 0.0426 GPa/K, which is slightly larger than that of pure Fe. The pressure interval
of the two-phase region is about 6 GPa at a constant temperature, implying that the previous estimates by laser-heated DAC
experiments of 10–20 GPa were overestimated. The two-phase region of fcc + hcp would be limited to a pressure of about 120 GPa even in Fe–15 wt%Ni, excluding the possibility of the existence of the fcc phase in the inner core if the simple linear extrapolation of the two-phase region is applied. The pressure and temperature
dependences of the c/a axial ratio of the hcp phase in Fe–9.7 wt% Ni are generally consistent with those in pure Fe, suggesting that Ni has minor effects on the c/a ratio. |
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