17:15 〜 18:30
[SMP26-P02] ε-FeOOHの弾性波速度に対する圧力誘起鉄スピン転移の影響
キーワード：ε-FeOOH、High pressure、Spin transition、Inelastic X-ray scattering
ε-FeOOH is a high-pressure polymorph of α-FeOOH (goethite), and has been reported to be a crucial candidate of the water carriers into deep mantle via subduction (Nishi et al., 2019; Liu et al., 2019). Despite the importance of ε-FeOOH for water transportation, its elastic property is still unclear. At pressure of ∼45 GPa, the phase shows the electronic high-spin to low-spin transition of iron which leads the density to higher along compression (Gleason et al., 2013). The elasticity is expected to be significantly affected by the spin transition.
We present the effect of the spin transition on the elastic wave velocity of ε-FeOOH under pressure. The sample was polycrystalline ε-FeOOH, which was synthesized in advance from a powder of α-FeOOH at a high-pressure and high-temperature condition. A pellet of the sample was enclosed in each sample chamber of a diamond anvil cell with either NaCl or glycerol as a pressure medium. The high-pressure experiments have been conducted at BL35XU in SPring-8 (Baron et al., 2000), and the longitudinal wave velocity, VP, and density were measured up to a pressure 56 GPa at room temperature, combining non-resonant Inelastic X-ray scattering (IXS) spectroscopy and powder X-ray diffraction (XRD) method. Incident X-ray was monochromatized to 17.794 keV and focused to 16 × 16 μm. Scattered X-ray was analyzed by 12 analyzer crystals whose scattering angles correspond to the momentum transfer Q of 4.2–8.4 nm-1, and the dispersion curve of the longitudinal acoustic phonon was determined. Diffracted X-ray was captured by a flat panel detector and the unit-cell parameters of the sample were obtained. VP, which is the gradient of the dispersion curve at Q → 0, was yielded by fitting the curve with a sine function. The pressure was calculated using the equations of state of the sample (Thompson et al., 2020).
In the pressure range below 20 GPa, VP of ε-FeOOH in this study was consistent with that of a previous study using the ultrasonic method and multi-anvil apparatus (Ikeda et al., 2019). A ~4% drop in VP was observed at pressures 40, 41, and 42 GPa, which is ~4 GPa below the spin transition in ε-FeOOH. This drop is considered to be the results of a decrease of shear modulus, or of an unstable state of electrons at around the transition pressure. VP in the pressure range 45–56 GPa (the low-spin state) overlapped with the extrapolated VP from the pressure below 40 GPa.
Reference:
Baron, A.Q.R., Tanaka, Y., Goto, S., Takeshita, K., Matsushita, T. and Ishikawa, T. (2000) An X-ray scattering beamline for studying dynamics. Journal of Physics and Chemistry of Solids, 61, 461–465.
Gleason, A.E., Quiroga, C.E., Suzuki, A., Pentcheva, R. and Mao, W.L. (2013) Symmetrization driven spin transition in ε-FeOOH at high pressure. Earth and Planetary Science Letters, 379, 49–55.
Ikeda, O., Sakamaki, T., Ohashi, T., Goto, M., Higo, Y. and Suzuki, A. (2019) Sound velocity measurements of ε-FeOOH up to 24 GPa. Journal of Mineralogical and Petrological Sciences, 114, 155–160.
Liu, X., Matsukage, K.N., Nishihara, Y., Suzuki, T. and Takahashi, E. (2019) Stability of the hydrous phases of Al-rich phase D and Al-rich phase H in deep subducted oceanic crust. American Mineralogist, 104, 64–72.
Nishi, M., Tsuchiya, J., Kuwayama, Y., Arimoto, T., Tange, Y., Higo, Y., Hatakeyama, T. and Irifune, T. (2019) Solid solution and compression behavior of hydroxides in the lower mantle. Journal of Geophysical Research: Solid Earth, 124, 10231–10239.
Thompson, E.C., Davis, A.H., Brauser, N.M., Liu, Z., Prakapenka, V.B. and Campbell, A.J. (2020) Phase transitions in ε-FeOOH at high pressure and ambient temperature. American Mineralogist, 105, 1769–1777.
We present the effect of the spin transition on the elastic wave velocity of ε-FeOOH under pressure. The sample was polycrystalline ε-FeOOH, which was synthesized in advance from a powder of α-FeOOH at a high-pressure and high-temperature condition. A pellet of the sample was enclosed in each sample chamber of a diamond anvil cell with either NaCl or glycerol as a pressure medium. The high-pressure experiments have been conducted at BL35XU in SPring-8 (Baron et al., 2000), and the longitudinal wave velocity, VP, and density were measured up to a pressure 56 GPa at room temperature, combining non-resonant Inelastic X-ray scattering (IXS) spectroscopy and powder X-ray diffraction (XRD) method. Incident X-ray was monochromatized to 17.794 keV and focused to 16 × 16 μm. Scattered X-ray was analyzed by 12 analyzer crystals whose scattering angles correspond to the momentum transfer Q of 4.2–8.4 nm-1, and the dispersion curve of the longitudinal acoustic phonon was determined. Diffracted X-ray was captured by a flat panel detector and the unit-cell parameters of the sample were obtained. VP, which is the gradient of the dispersion curve at Q → 0, was yielded by fitting the curve with a sine function. The pressure was calculated using the equations of state of the sample (Thompson et al., 2020).
In the pressure range below 20 GPa, VP of ε-FeOOH in this study was consistent with that of a previous study using the ultrasonic method and multi-anvil apparatus (Ikeda et al., 2019). A ~4% drop in VP was observed at pressures 40, 41, and 42 GPa, which is ~4 GPa below the spin transition in ε-FeOOH. This drop is considered to be the results of a decrease of shear modulus, or of an unstable state of electrons at around the transition pressure. VP in the pressure range 45–56 GPa (the low-spin state) overlapped with the extrapolated VP from the pressure below 40 GPa.
Reference:
Baron, A.Q.R., Tanaka, Y., Goto, S., Takeshita, K., Matsushita, T. and Ishikawa, T. (2000) An X-ray scattering beamline for studying dynamics. Journal of Physics and Chemistry of Solids, 61, 461–465.
Gleason, A.E., Quiroga, C.E., Suzuki, A., Pentcheva, R. and Mao, W.L. (2013) Symmetrization driven spin transition in ε-FeOOH at high pressure. Earth and Planetary Science Letters, 379, 49–55.
Ikeda, O., Sakamaki, T., Ohashi, T., Goto, M., Higo, Y. and Suzuki, A. (2019) Sound velocity measurements of ε-FeOOH up to 24 GPa. Journal of Mineralogical and Petrological Sciences, 114, 155–160.
Liu, X., Matsukage, K.N., Nishihara, Y., Suzuki, T. and Takahashi, E. (2019) Stability of the hydrous phases of Al-rich phase D and Al-rich phase H in deep subducted oceanic crust. American Mineralogist, 104, 64–72.
Nishi, M., Tsuchiya, J., Kuwayama, Y., Arimoto, T., Tange, Y., Higo, Y., Hatakeyama, T. and Irifune, T. (2019) Solid solution and compression behavior of hydroxides in the lower mantle. Journal of Geophysical Research: Solid Earth, 124, 10231–10239.
Thompson, E.C., Davis, A.H., Brauser, N.M., Liu, Z., Prakapenka, V.B. and Campbell, A.J. (2020) Phase transitions in ε-FeOOH at high pressure and ambient temperature. American Mineralogist, 105, 1769–1777.