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Science 1 December 1995:
Vol. 270. no. 5241, pp. 1473 - 1475
DOI: 10.1126/science.270.5241.1473
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Reports

Phase Diagram of Iron by in Situ X-ray Diffraction: Implications for Earth's Core

C. S. Yoo (1),  J. Akella,  A. J. Campbell (2),  H. K. Mao,  R. J. Hemley

The phase diagram of iron has been studied to 130 gigapascals (1 gigapascal = 10^4 atmospheres) and 3500 kelvin by a combined laser-heated diamond-anvil cell and x-ray diffraction technique that provides direct identification of the solid phases. Iron in the hexagonal close-packed (hcp) phase (-Fe) is stable from 50 to at least 110 gigapascals at high temperatures. The wide stability field of -Fe indicates that this polymorph should currently be considered the most relevant solid phase for Earth's core. The triple point between the , , and liquid phases is located at 2500 ± 200 kelvin and 50 ± 10 gigapascals. There is evidence for a phase with a double hcp structure below 40 gigapascals and for another transition above 110 gigapascals and 3000 kelvin.


C. S. Yoo and J. Akella, Lawrence Livermore National Laboratory, University of California, Livermore, CA 94551, USA.
A. J. Campbell, H. K. Mao, R. J. Hemley, Geophysical Laboratory and Center for High Pressure Research, Carnegie Institute, Washington, DC 20015, USA.
(1) To whom correspondence should be addressed.
(2) Present address: G.E. Superabrasives, 6325 Huntley Road, P.O. Box 568, Worthington, OH 43085, USA.


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