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Clarification of Metallic Transition of Iron(II) Oxide (FeO) with Rock-Salt-Type Structure Induced by High Pressure and High Temperature (Press Release)

Release Date
13 Jan, 2012
  • BL10XU (High Pressure Research)
-FeO existing in the lowermost mantle affects the earth’s rotation.

Osaka University
Japan Synchrotron Radiation Research Institute (JASRI)

Kenji Ohta (recipient of Research Fellowship for Young Scientists supported by the Japan Society for the Promotion of Science) and Katsuya Shimizu (Professor) of the Center for Quantum Science and Technology under Extreme Conditions, Osaka University, found that iron(II) oxide (FeO) undergoes an insulator-metal transition*1 at a high pressure and high temperature exceeding 70 GPa and 1,600 oC, respectively, without undergoing a structural phase transition. They also found, for the first time in the world, that this metal transition is caused by a newly discovered mechanism from a high-pressure and high-temperature experiment using the high-brilliance synchrotron radiation of SPring-8*2 and by theoretical calculation. These results were obtained in cooperation with scientists from the Carnegie Institute for Science, Tokyo Institute of Technology, Japan Agency for Marine-Earth Science and Technology, Rutgers University, and JASRI.

FeO is an important component of the earth’s mantle and outer core. The newly discovered metal transition of FeO that can occur at the pressure and temperature of the lowermost mantle strengthens the electromagnetic interactions between the mantle and core, which may affect the earth’s rotation. This new mechanism for the insulator-metal transition is expected to lead to a greater understanding of the state of strong electromagnetic interactions between the electrons in a material (a strongly correlated electron system), as studied in the field of condensed matter physics. The results of this study were published in Physical Review Letters, a journal published by the American Physical Society, on 12 January 2012.

"Experimental and Theoretical Evidence for Pressure-Induced Metallization in FeO with Rocksalt Type Structure"
Kenji Ohta, Ronald E. Cohen, Kei Hirose, Kristjan Haule, Katsuya Shimizu, Yasuo Ohishi
Physical Review Letters 108 published 12 January 2012

*1 Insulator-metal transition

An insulator-metal transition refers to a transition from an insulator, in which flow of current is resisted, to a metal.

*2 SPring-8
SPring-8 is a facility that generates the world’s highest-performance synchrotron radiation. It is located in Harima Science Garden City in Hyogo prefecture and is owned by RIKEN. JASRI is responsible for its operation, management, and support for users. The name SPring-8 is derived from Super Photon ring-8 GeV. Synchrotron radiation is the narrow and extremely powerful light that is obtained when the direction of electrons accelerated to close to the speed of light is bent using electromagnets. Research in a wide range of fields including nanotechnology, biotechnology, and their industrial applications has been carried out using the synchrotron radiation at SPring-8.



Fig. 1 Laser-heated diamond-anvil cell (A). A sample is compressed between a pair of diamond culets facing each other (B). A high pressure and high temperature comparable to those in the earth’s interior can be simulated by irradiating lasers on the sample at a high pressure.

Fig.2 Phase diagram of FeO at high pressures and temperatures
Fig. 2 Phase diagram of FeO at high pressures and temperatures

The solid line and thick dotted lines represent the transition boundary determined in this study (the gray belt shows the region of uncertainty of pressure and temperature). The symbols indicate the pressure and temperature conditions examined in this study (B1, rock-salt-type structure; rB1, rhombohedral rock-salt-type structure; B8, nickel-arsenide-type structure).

Fig.3 Experimental setup of time-domain interferometry and time spectra

Fig. 3 Change in electric conductivity of FeO with B1-type structure with pressure at high temperatures (blue, experimental data; black, data obtained by theoretical calculation) and electron state of FeO (inset)

For more information, please contact:
 Dr. Kenji Ohta
 Dr. Katsuya Shimizu

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