実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）Experimental Report

承認日 Date of Approval 2017/7/27
承認者 Approver Takanori Hattori
提出日 Date of Report 2017/7/26

課題番号 Project No. 2017A0093

装置責任者 Name of Instrument scientist

実験課題名 Title of experiment: Site occupancy and volume ofTakanori Hattoriinterstitial hydrogen atoms in iron hydride polymorphs

装置名 Name of Instrument/（BL No.）

実験責任者名 Name of principal investigator

Planet/BL11

Eiji Ohtani

実施日 Date of Experiment

所属 Affiliation

April 8th -20th, 2017Tohoku University
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.

The starting material was the same as that used for the previous proposal of 2016B, which was thepowdered sample of iron (99.9% purity, Wako pure chemical industries, Ltd) with a grain size about 300
um. The powdered Fe was compressed by a uniaxial hand press to the pressure of 100-200 MPa, and aniron disc with 3 mm diameter and 2.5 mm length was prepared for the starting material.

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

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

Experimental method:
A cubic high-pressure apparatus (Atsuhime) installed at BL11 was used for high pressure generation. An Fe discspecimen (3mm in diameter and 2.5mm in height) is placed at the center of a hydrogen-sealing capsule made ofNaCl (5.5mm in diameter and 8mm in height) with internal hydrogen sources of NH3BH3 pellets above andbelow. The NaCl capsule was inserted in a cylindrical graphite heater and embedded in a pressure-transmitting
medium made of ZrO2 (17-mm-edge cube). Two high pressure high temperature diffraction experiments was
conducted at around 9.5-12 GPa in the stability field of dhcp- and fcc-iron and 300-1200 K using anvils with a 7mm truncated edge length, and around 3.6-4 GPa and 850-1200 K using anvils with a 10 mm truncated edge
length in the stability field of fcc-Fe. Neutron diffraction data was corrected at high pressure and temperature.
Neutron-diffraction profiles were accumulated during the heating process. The temporal evolution of thediffraction profile was monitored at several fixed temperatures above the hydrogenation temperature of NH3BH3.
The composition and site occupancy of H atom in the fcc-and dhcp-lattice of FeHx were determined for the2. 実験方法及び結果（つづき） Experimental method and results (continued)

equilibrium state at a fixed pressure. The temperature was kept constant and the temporal
evolution of the diffraction profile was monitored to confirm that the solid solution of FeHx
reached equilibrium with the surrounding H2 fluid. The structure of FeHx and the content ofhydrogen were determined by Rietveld refinement.
Results and discussion
We have successfully determined the hydrogen atomic volume in iron hydride lattice at variouspressure and temperature. The phasetransition and hydrogenation of iron
were observed by dhcp-FeHx andfcc-FeHx phase, which are highpressure and high temperature phasesof FeHx. We have conducted two
separate runs. Run 1 was made in thepressure range around 9-12 GPausing the pressure cell for the cubicanvils with 7 mm truncated edge
length. Run 2 was made at around
3.6-4 GPa using the anvils with 10
mm truncated edge length.
Diffraction profiles obtained at 10.9
GPa and 750 K revealed that the four
typical peak intensities of dhcp-FeHx
can be fitted by FeHx with x values
greater than unity (x>1) model morereasonably. This process can beexplained as follows: After complete
filling (x=1) of the interstitial sites,hydrogen go into the lattice defectspace. Hydrogen atoms kicked outiron and appears to fill the vacantiron sites, and thus hydrogen atoms
becomes larger than unity. This mechanism is similar to hydrogen in TiHx compound. Figure 1
shows the change of hydrogen content x in FeHx (fcc and dhcp-FeHx), The amount of hydrogen,x, increases with increasing pressure and decreasing temperature. The amount of hydrogen, x,exceeds unity in dhcp-Fe at pressures greater than 10 GPa.