title: Abnormal elastic and vibrational behaviors of magnetite at high pressures.
abstract: Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe(2+)-Fe(3+)-Fe(2+) ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature.
authors.affiliation: 1] Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, TX 78712, USA [2] Texas Materials Institute, The University of Texas at Austin, TX 78712, USA [3] Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai, China.
authors.forename: Jung-Fu
authors.initials: JF
authors.lastname: Lin
authors.affiliation: 1] Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai, China [2] Institute of Physics, Chinese Academy of Sciences, Beijing, China.
authors.forename: Junjie
authors.initials: J
authors.lastname: Wu
authors.affiliation: Institute of Physics, Chinese Academy of Sciences, Beijing, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhu
authors.affiliation: 1] Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, TX 78712, USA [2] Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Zhu
authors.initials: Z
authors.lastname: Mao
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Ayman H
authors.initials: AH
authors.lastname: Said
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Bogdan M
authors.initials: BM
authors.lastname: Leu
authors.affiliation: 1] Texas Materials Institute, The University of Texas at Austin, TX 78712, USA [2] Department of Mechanical Engineering, The University of Texas at Austin, TX 78712, USA [3] Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Jinguang
authors.initials: J
authors.lastname: Cheng
authors.affiliation: Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Uwatoko
authors.affiliation: Institute of Physics, Chinese Academy of Sciences, Beijing, China.
authors.forename: Changqing
authors.initials: C
authors.lastname: Jin
authors.affiliation: 1] Texas Materials Institute, The University of Texas at Austin, TX 78712, USA [2] Department of Mechanical Engineering, The University of Texas at Austin, TX 78712, USA.
authors.forename: Jianshi
authors.initials: J
authors.lastname: Zhou