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
15 November 2017

課題番号 Project No.

装置責任者 Name of responsible person

2017A0008

Prof. S. Itoh

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Phonon dynamics of Mg alloys with synchronized long-period

HRC/(BL12)

stacking ordered structure

実施日 Date of Experiment

実験責任者名 Name of principal investigator

31.03.2017-19.04.2017

Shinya Hosokawa
所属 Affiliation
Kumamoto 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.
Mg97Zn1Y2, Polycrystal
Mg85Zn6Y9, Polycrystal

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.

Recently, a new series of Mg alloys [1] with the microstructure containing a synchronized long-period
stacking ordered (LPSO) structure, the so-called KUMADAI Magnesium, has been attracted considerable
attention due to the excellent mechanical properties. By adding a small amount of Zn and rare-earth metals (Y orGd) impurities, light weighted Mg metal of soft and flammable becomes much hardened and non-flammable. Bytaking such excellent natures, the new Mg alloys can be used for body materials of subways or even aircrafts.
A scanning transmission electron microscope (STEM) image obtained by Abe et al. [2] showed light and dark
atomic image stripes, which represent the impurity-rich and -poor regions, respectively. Changes in stacking
lattice order are also observed at the center of the light stripes, and thus, the concentration of the impurities andthe modulation of the lattice stacking order are synchronized. Excellent mechanical properties of the LPSO
phases were understood to be originated from such interesting microstructures.
Macroscopic elastic properties of these Mg alloys were intensively investigated by several groups [3].
However, the microscopic information on the dynamics of this material is still lacking. Furthermore, element
selective dynamical experiments have not been planned so far. Due to the difference of the scatteringcross-sections, inelastic neutron scattering (INS) emphasizes the dynamics of majority Mg atoms, while inelastic
x-ray

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2. 実験方法及び結果（つづき） Experimental method and results (continued)
scattering (IXS) enhances that of impurities, in particular Y atoms. A complementary use of neutron and x-ray
sources is necessary for this study. We already performed the IXS experiments at BL35XU/SPring-8 [4-6]. Theenergy resolution is about 1.6 meV.
In the last INS experiment at J-PARC [5], we used incident neutrons with a high energy Ei of 200 meV toobserve the overall spectral features of the INS spectra. In turn, however, the energy resolution was about 6meV, a large difference from the IXS one of about 1.6 meV. In this project, we carried out the INS experimentson the Mg97Zn1Y2 and Mg85Zn6Y9 polycrystals using Ei = 100 meV. Owing to the improvement of thespectrometer, the resolution width rose to be about 2 meV, similar to that of IXS. In this experimental round, weconcentrate to precisely measure the transverse acoustic (TA) modes in combined with the longitudinal acoustic(LA) modes at the large Q values.
Figure 1 shows the S(Q,ω) spectra in the ω-Q plane on (a) Mg97Zn1Y2 and (b) Mg85Zn6Y9 polycrystals. As
seen in the figures, the dispersion relations of the TA and LA modes are seen in the first and second Brillouinzone below Q < ~2.4 Å-1 as observed in the IXS spectra [4-6]. Moreover, the dispersion-less excitation modes
are observed at about 10 and 17 meV in the spectrum of (b) Mg85Zn6Y9 polycrystal, which were again detectedin the IXS spectra [4-6].
In our previous combined INS and IXS experiments, we expected that the TA modes are mainly composed of
the vibrational motions of host Mg atoms, and the dispersion-less modes are highly related to those of theimpurity atoms. We will confirm the above speculation by using newly obtained INS data in this project.

Fig. 1 The S(Q,ω) spectra in the ω-Q plane on polycrystalline (a) Mg97Zn1Y2 and (b) Mg85Zn6Y9 at Ei = 100
meV.
[1] Y. Kawamura et al., Mater. Trans. 42, 1172 (2001).
[2] E. Abe et al., Philos. Mag. Lett. 91, 690 (2011).
[3] For example, M. Tane et al., Acta Mater. 61, 6338 (2013).
[4] S. Hosokawa et al., Materials Transaction 56, 914 (2015).
[5] S. Hosokawa et al., J. Alloys Compd. 695, 426 (2017).
[6] S. Hosokawa et al., Acta Mater., submitted.
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