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1 Institute for Study of the Earths Interior, Okayama University, Misasa, Tottori-ken 682-0193, Japan
2 RIKEN Harima Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
3 Center for Adanced Radiation Sources, The University of Chicago, Argonne, Illinois 60439, U.S.A.
4 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan
5 Japan Synchrotron Radiation Research Institute, Hyogo-ken 678-5198, Japan
Correspondence: * E-mail: eiito{at}misasa.okayama-u.ac.jp
Phase equilibria of Fe2O3 have been studied up to 58 GPa and 1400 K using the Kawai-type multi anvil apparatus equipped with sintered diamond anvils. Identification of phases and pressure determination has been carried out by means of in situ X-ray observation using synchrotron radiation at SPring-8. Hematite (phase I) successively transforms to the Rh2O3(II)-type structure (phase II) and then to an orthorhombic structure (phase III) with increasing pressure. The transformations of hematite into high-pressure phases have been observed only at temperatures higher than 500 K, which is not concordant with previous results obtained by using the diamond anvil cell. Volume changes accompanied by the I–II and II–III transformations are calculated to be –2.8 and –5.0%, respectively. The phase boundary between I and II phases and that between II and III have been proposed to be P (GPa) = –0.015 T (K) + 44.2 and P (GPa) = –0.005 T (K) + 48.7, respectively. Possible correlation between a Mott transition and the phase stabilities may be concealed at room temperature due to slow reaction kinetics of the structural transformations.
Key Words: High-pressure phase equilibria Fe2O3 Kawai-cell sintered diamond in situ X-ray observation
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