承認日Date of Approval 2017/4/10

Experimental Report

承認者Approver Kaoru Shibata
提出日Date of Report 2017/4/10

Project No.

Name of responsible person

2016B0159

Kaoru SHIBATA
Title of experiment

Name of Instrument/ BL No.

Transportation of hydrogen at high temperatures in the
deep Earth by quasielastic neutron scattering

DNA / BL02
Date of Experiment

February 15-23, 2017

Name of principal investigator

Takuo OKUCHI
Affiliation

Institute for Planetary Materials, Okayama University

Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
Name of sample(s) and chemical formula, or compositions including physical form.

Dense Hydrous Magnesium Silicate Phase E [Mg2+xSi1+yH4-2x-4yO6], powder
Serpentine [(Mg,Fe)3Si2O5(OH)4], powder

Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

The project was technically supported by our recent progress on a mass-production schemeof hydrous deep-Earth minerals of excellent quality and quantity (Okuchi et al., Am. Mineral.
2015). A single-phase sample powder of dense hydrous magnesium silicate (DHMS) phase E wassynthesized by accumulating the products of several independent synthesis runs all using thisscheme. As for more details for these synthesis runs, we used a scaled-up Kawai-type cell at
Okayama University along with 46 mm-sized cubic carbide anvils and a 18/10 cell assembly. Eachsample made of a mixture of Mg(OH)2 and SiO2 powders in the molar ratio of 2:1 was sealed intoa gold tube capsule of 5 mm outside diameter, which contained >80 mg of the mixture to becompressed to 15 GPa pressure, that corresponds to the condition where DHMS phase E exists
inside the Earth. After loading this pressure, the sample was heated by applying electronic current
to a cylindrical LaCrO3 semiconducting furnace, which was installed inside the cell to surround thegold capsule. After the heating, the electric current was cut-off and then the synthesis product was1

Experimental method and results (continued)

recovered into ambient condition.Each product was then separately evaluated by powder x-ray
diffraction to confirm whether the recovered DHMS phase E powder was single-phase, chemicallyhomogeneous, as well as highly crystalline. Among all these recovered products, we have selected
only the highest-quality ones, which were then mixed up together to prepare the sample powder for
quasi-elastic neutron scattering measurements (QENS).
DNA spectrometer has the highest energy resolution among available instruments for QENS.
By our previous efforts, DNA has been proved to provide sufficient energy resolution to analyze
the slow dynamics of chemically-bonded hydrogen, as well as high intensity and extremely-low
background to measure the mass-limited synthetic sample of deep-Earth hydrous minerals. In
order to control the sample temperatures, we used a top-loading type cryo-furnace which wasoperated up to 480 K without problem. A representative S(Q,E) of DHMS phase E obtained at
DNA was shown below. The blue-colored Lorentz peak showed mobile hydrogen component.

Our specific goal in the current project was to determine hydrogens local and translational
dynamics within DHMS phase E at higher temperature conditions, which are more relevant to thephysical environments of hydrous minerals in the deep Earth. We are now analyzing the results todetermine relaxation times and hopping distances of local and translational motions of hydrogen ateach measured temperature, as well as activation energies of these motions. We are recently
demonstrating that crystal structures of prevailing deep-Earth hydrous minerals quite often involve
dynamically-disordered hydrogen sites of partially-filled occupancy (Purevjav et al., Geophys.
Res. Lett., 2014; Okuchi et al., High Pressure. Res., 2014), which are also including the structureof DHMS phase E (Tomioka et al., Phys. Chem. Mineral., 2016). Such characteristics of thehydrogen sites of DHMS phase E will result in anomalously-fast transportation dynamics ofhydrogen, which is suggested by the significant dynamics alredy emerging at 480 K as shown in
the figure above.

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