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。 ）MLF Experimental Report

提出日 Date of Report
装置責任者 Name of responsible person

課題番号 Project No.

Prof. Yasuhiro Miyake

2012A0063
実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）µ SR and µ SR studies of hydrogen behavior in a new oxyhydrideMuon D1

BaTi(O,H)3

実施日 Date of Experiment

実験責任者名 Name of principal investigator2012/05/20-2012/05/25+-Takashi Ito
所属 Affiliation
Japan Atomic Energy Agency
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.
(1) BaTiO2.5H0.5, 3g, a pellet wrapped with an Al foil
(2) BaTiO3, 1.2g, two pieces of single crystalline samples wrapped with Al foils

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.

(1) µ+SR in BaTiO2.5H0.5
A φ24 mm pellet of BaTiO2.5H0.5 was mounted on a silver sample holder of a conventional 4He flow
cryostat. ZF/LF-µ+SR measurements were performed at the D1 area using a double-pulsed muon beam. Figure 1
shows a typical ZF-µ+SR spectrum at low temperatures below 100 K. The shaded area indicates an instrumental
background determined by using a reference sample. Almost all the remaining signal damps significantly within
the time window, indicating that hydride ions randomly distribute over the whole volume of the specimen. Anoscillating pattern was clearly observed, suggesting formation of a 1H-µ spin entangled state [R. Kadono et al.,PRL 100, 026401 (2008)]. The ZF-µ+SR spectra at low temperatures were successfully fitted with the following
function, As[p2S e-λt G2S(t;ωd)+(1-p2S)exp(-∆2t2)] + ABG, where As and ABG are partial asymmetries for the sample
and the instrumental background, p2S is the fractional weight for the two spin entangled state, G2S(t) is therelaxation function for the two spin entangled state, ωd is the angular frequency, and λ and ∆ are the relaxation
rates. The best fit for the data at 30 K is shown in Fig. 1 with the solid line. The fitting parameters are almost
constant below 100 K. An H--µ distance of the two spin entangled state was estimated to be ~0.17 nm from ωd.
1

2. 実験方法及び結果（つづき） Experimental method and results (continued)
This agrees well with a distance between an interstitial protonic impurity site and a second nearest neighboranion site in pure BaTiO3. Thus, we conclude that muons implanted into BaTiO2.5H0.5 stay at the interstitial site
as µ+ as shown in Fig. 2 and microscopically coexist with the H- ions at the anion sites in the same lattice for atleast several tens of µs. This suggests a possibility to form hydroxyhydrides, where both H+ and H- are present inthe same lattice.

Fig.2: A schematic illustration of the µ+ sitein BaTiO2.5H0.5 below 100 K.
Fig.1: The ZF-µ+SR spectrum of BaTiO2.5H0.5 at 30 K.

(2) µ+SR in BaTiO3
ZF/LF/TF-µ+SR measurements on pure BaTiO3 were performed at the D1 area in order to compare withthe µ+SR results in BaTiO2.5H0.5. Two pieces of single-crystalline samples of BaTiO3 covering the cross-sectional
area of 10x20mm2 was mounted on a silver sample holder of a conventional 4He flow cryostat. Fast muon spin
relaxation was observed at low temperatures, indicating muonium formation. A LF-decoupling study revealed
that the hyperfine coupling constant of the muonium in BaTiO3 is considerably smaller than that in vacuum,suggesting a shallow muonium state. We also carried out TF-µ+SR measurements in a magnetic field of 123 Oe
to obtain spectroscopic evidence of the shallow muonium state. A frequency splitting suggesting the shallow
muonium state was observed, but this is not so clear due to the double pulse structure of the muon beam.
*A new proposal for shallow muonium hunting in pure BaTiO3 was submitted to J-PARC PAC in order to obtain clear evidence ofthe shallow donor state in BaTiO3. The proposal was recently approved.

(3) µ-SRThe µ-SR measurements planned in the proposal has not been done yet since the allocated beamtime was
not sufficient for such an experiment. An up-grade of the spectrometer or beam intensity is necessary to performµ−SR measurements in a few days of beamtime.

2