[SMP36-06] ガヤナイトの高温高圧下中性子回折実験：含水鉱物中の水素結合の温度圧力依存性
キーワード：ガヤナイト、中性子回折、高圧、水素結合
Water is transported to the deep mantle by hydrous minerals in a subduction zone. Hydrogen bonding in hydrous minerals greatly affects their elastic properties such as compressibility, seismic velocity, and so on [e.g., 1,2]; it is important for us to clarify the effects of water into the properties of deep-mantle minerals. Under high-pressure conditions, a lot of hydrous minerals have a distorted rutile-type structure such as δ-AlOOH and ε-FeOOH. Recently, pressure-induced hydrogen bond (H-bond) symmetrization was experimentally observed in δ-AlOOH at ~18 GPa and room temperature [3]. However, the behavior of hydrogen in distorted rutile-type hydrous minerals at high temperature has not been clarified. Guyanaite (β-CrOOH) has also a distorted rutile-type structure and its H-bonds are significantly shorter than that of δ-AlOOH and other distorted rutile-type hydrous phases at ambient condition [e.g., 3,4]. Thus, H-bond symmetrization in guyanaite is expected to occur at relatively low pressure. Guyanaite can serve as an analogue material for predicting H-bond symmetrization in distorted rutile-type hydrous minerals. In this study, we conducted high-PT neutron diffraction measurements on guyanaite and investigated P-T dependence of hydrogen bonding in guyanaite.
Deuterated guyanaite (β-CrOOD) was used as a sample to reduce incoherent scattering from hydrogen. The sample was hydrothermally synthesized from the mixture of CrO2, D2O and a reducing agent (COOD)2·2D2O. Formation of the deuterated sample was confirmed from infrared absorption spectra and powder XRD. Neutron diffraction measurements at high-PT conditions up to 11 GPa and 1000 K were performed using a six-axis multi-anvil press installed at BL11, MLF, J-PARC. The structure of β-CrOOD was refined by every P-T condition using Rietveld method. High-PT XRD measurements up to 7.6 GPa and 900 K were also performed at NE7A, PF-AR, KEK. P-V-T data were fitted to high-temperature Birch–Murnaghan equation of state.
Thermoelastic parameters of β-CrOOD were determined to be K300 = 204(4) GPa (Kp = 4), dK/dT = –0.033(9) GPa/K, and α = 3.05(17) × 10-5 /K, where α is expressed as VT = V300 × exp{α × (T − 300)}. These values were comparable to those of β-CrOOH [5]. At 300 K, the axal ratio a/b increased with pressure up to ~4 GPa, but it became constant above ~4 GPa. This behavior was found in the process of H-bond symmetrization in δ-AlOOH [3]. At higher temperature, the change in the gradient of a/b shifted to higher pressure. The O…O and D…O distances elongated with increasing temperature, whereas the O-D bond distance shortened with increasing temperature. It means that the D…D distance gets longer with increasing temperature. This result suggests that the pressure of H-bond symmetrization under mantle conditions would be higher than that under high-P and room-T conditions. When we consider the effect of the H-bond symmetrization on seismic observation, we would need to carefully take the temperature dependence into account.
[1] J. Tsuchiya, T. Tsuchiya, S. Tsuneyuki, and T. Yamanaka (2002) Geophys. Res. Lett., 29, 1909.
[2] A. Sano-Furukawa, T. Yagi, T. Okada, H. Gotou, and T. Kikegawa (2012) Phys. Chem. Minerals, 39, 375–383.
[3] A. Sano-Furukawa, T. Hattori, K. Komatsu, H. Kagi, T. Nagai, J.J. Molaison, A.M. dos Santos, and C.A. Tulk (2018) Sci. Rep., 8, 15520.
[4] T. Fujihara, M. Ichikawa, T. Gustafsson, I. Olovsson, and T. Tsuchida (2002) J. Phys. Chem. Solids, 63, 309–315.
[5] C. Shito, K. Okamoto, Y. Sato, R. Watanabe, T. Ohashi, K. Fuchizaki, T. Kuribayashi, and A. Suzuki (2019) High Press. Res., 39, 499–508.
Deuterated guyanaite (β-CrOOD) was used as a sample to reduce incoherent scattering from hydrogen. The sample was hydrothermally synthesized from the mixture of CrO2, D2O and a reducing agent (COOD)2·2D2O. Formation of the deuterated sample was confirmed from infrared absorption spectra and powder XRD. Neutron diffraction measurements at high-PT conditions up to 11 GPa and 1000 K were performed using a six-axis multi-anvil press installed at BL11, MLF, J-PARC. The structure of β-CrOOD was refined by every P-T condition using Rietveld method. High-PT XRD measurements up to 7.6 GPa and 900 K were also performed at NE7A, PF-AR, KEK. P-V-T data were fitted to high-temperature Birch–Murnaghan equation of state.
Thermoelastic parameters of β-CrOOD were determined to be K300 = 204(4) GPa (Kp = 4), dK/dT = –0.033(9) GPa/K, and α = 3.05(17) × 10-5 /K, where α is expressed as VT = V300 × exp{α × (T − 300)}. These values were comparable to those of β-CrOOH [5]. At 300 K, the axal ratio a/b increased with pressure up to ~4 GPa, but it became constant above ~4 GPa. This behavior was found in the process of H-bond symmetrization in δ-AlOOH [3]. At higher temperature, the change in the gradient of a/b shifted to higher pressure. The O…O and D…O distances elongated with increasing temperature, whereas the O-D bond distance shortened with increasing temperature. It means that the D…D distance gets longer with increasing temperature. This result suggests that the pressure of H-bond symmetrization under mantle conditions would be higher than that under high-P and room-T conditions. When we consider the effect of the H-bond symmetrization on seismic observation, we would need to carefully take the temperature dependence into account.
[1] J. Tsuchiya, T. Tsuchiya, S. Tsuneyuki, and T. Yamanaka (2002) Geophys. Res. Lett., 29, 1909.
[2] A. Sano-Furukawa, T. Yagi, T. Okada, H. Gotou, and T. Kikegawa (2012) Phys. Chem. Minerals, 39, 375–383.
[3] A. Sano-Furukawa, T. Hattori, K. Komatsu, H. Kagi, T. Nagai, J.J. Molaison, A.M. dos Santos, and C.A. Tulk (2018) Sci. Rep., 8, 15520.
[4] T. Fujihara, M. Ichikawa, T. Gustafsson, I. Olovsson, and T. Tsuchida (2002) J. Phys. Chem. Solids, 63, 309–315.
[5] C. Shito, K. Okamoto, Y. Sato, R. Watanabe, T. Ohashi, K. Fuchizaki, T. Kuribayashi, and A. Suzuki (2019) High Press. Res., 39, 499–508.