実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report2017.6.5.

課題番号 Project No.

装置責任者 Name of responsible person

2016B0062

Shuki Tori

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Role of disorders in the reduction of thermal conductivity for theSuper

intermetallic compounds with disordered Na atoms in helical

Diffractometer (SuperHRPD) / BL 08

tunnels

実施日Date of Experiment

実験責任者名 Name of principal investigator

2017/02/11 ~ 2017/02/14

HighResolution

PowderTakahiro Yamada
所属 Affiliation
Tohoku 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.

Ternary intermetallic compound in Na-Ga-Sn system, Na2+xGa2+xSn4-x, x=0.0, 0.19, powder (invanadium cells)
Ternary intermetallic compound in Na-In-Sn system, Na2In2Sn4, powder (in a vanadium cell)

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
Time-of-flight (TOF) neutron powder diffraction data of ternary intermetallic compounds in Na-Ga-Sn andNa-In-Sn systems, which can be considered as candidates for thermoelectric materials due to the low thermalconductivities, were measured by a high-resolution neutron powder diffractometer Super-HRPD installed at thebeam line BL08 of J-PARC facility. The powdered samples of the intermetallic compounds, Na2+xGa2+xSn4-x (x =0.0, 0.19) and Na2In2Sn4 which were prepared by solid state reaction in Tohoku University, were sealed into
vanadium cylindrical cells with a diameter of 6 mm and a height of 60 mm in a glove box filled with a helium
atmosphere. The sample cells were installed in a closed-cycle helium cryostat. The TOF neutron powder
diffraction measurements were performed at approximately 10, 50, 100, 200, and 280 K for each sample in orderto get information on the atomic displacement parameters (ADPs) for Na atom, of which the static and/or dynamic
positional disorders probably play an important role in the reduction of lattice thermal conductivity of thecompounds. The crystal structures varying temperature were analyzed using a Rietveld analysis program, ZRietveld (ver. 1.0.0).
12. 実験方法及び結果（つづき） Experimental method and results (continued)
Results
The measured diffraction patterns of Na2+xGa2+xSn4-x (x = 0 and 0.19) and Na2In2Sn4 were explained well byreported crystal structures having tunnel frameworks formed by Ga/Sn or In/Sn atoms with a hexagonal cell [1]and an orthorhombic cell [2], respectively. The anisotropic atomic displacement parameters (ADPs) weresuccessfully refined for Na and Ga/Sn sites of Na2+xGa2+xSn4-x (x = 0.19), while only isotropic ADPs could be
refined for those of Na2+xGa2+xSn4-x (x = 0). The difference in the analytical results for the ADPs are probably
due to the crystallinity of the powdered samples. Unfortunately, the measured diffraction data of Na2In2Sn4 were
statistically poor for the analysis of ADPs of Na atoms due to the anomalously large neutron mass absorption ofthe In atom.
The refined equivalent isotropic ADPs, Ueq, of Na site and Ga/Sn site of Na2+xGa2+xSn4-x (x = 0.19) were plottedin Figure 1. The values of Ueq at 12–282 K are over five times larger than the those of the Ga/Sn site. The Ueqvalues are consistent with the values of the ADPs of Na atom determined from the single crystal X-ray diffraction
data measured for Na2+xGa2+xSn4-x (x = 0.24) at 93–303 K [1]. The characteristic Einstein temperature (θE) anddisorder parameter (d) of Na atom estimated from the ADPs
in the measurement range were θE = 110(2) K and dNa =0.156(7) Å, which were closed to the values (θE = 105 K
and dNa = 0.16 Å) obtained from the single crystal XRD [1].
They indicated that the compound with x = 0.19 has both ofthe dynamic and static positional disorder of Na atoms in
the Na site.
Figure 2 shows the well-refined crystal structures of
Na2+xGa2+xSn4-x (x = 0.19) at 282 K and 12 K drawing withanisotropic atomic displacement ellipsoids perpendicular toand along tunnel direction. The displacement ellipsoids of
the Na site largely elongate along the tunnels, whereas theellipsoids of Ga/Sn site are almost spherical. The volume of
the Na site ellipsoids was larger than the volume of Ga/SnFig. 1. Isotropic ADPs of Na (open marks) and Ga/Sn(close marks) sites refined from powder neutron
diffraction of Na2+xGa2+xSn4-x with x = 0.19 (diamonds).
The data refined from single crystal X-ray diffraction ofNa2+xGa2+xSn4-x with x = 0.24 (circles) in Ref. 1 weredrawn.

site ones, and became smaller with keeping the elongatedshape until at 12 K. They indicate that large static disorderwas existed along tunnel direction even at low temperature.
More detailed structural analysis considering thepossibility of the distortion of the hexagonal lattice, which
was suggested by a slight broadening of some peaks, are
now in progress.
References[1] T. Yamada, H. Yamane, H. Nagai, Adv. Mater., 27, 4708 (2015).
[2] W. Blase, G. Cordier, R. Knipe, R. Schmidt, Z. Naturforsch. 44b,505 (1989).

2Fig. 2. Crystal structures of Na2+xGa2+xSn4-x (x = 0.19) at282 K (a) and 12 K (b). Displacement ellipsoids aredrawn at 75% probability level.