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 Report2018.2.6

課題番号 Project No.

装置責任者 Name of responsible person

2017A0114

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 the SuperHigh

Resolution

Powderintermetallic compounds with disordered Na atoms in helical Diffractometer (SuperHRPD) / BL 08
tunnels
実験責任者名 Name of principal investigator

実施日 Date of Experiment

Takahiro Yamada

2017.11.7–2017.11.12

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 compounds in Na-Zn-Sn system, tI-Na2ZnSn5 powder and hP-Na2ZnSn5
powder (in vanadium cells)
Ternary intermetallic compound in Na-Al-Sn system, Na2+xAl2+xSn4−x (x=−0.18) powder (in avanadium 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-Zn-Sn and Na-Al-Sn systems, which can be considered as candidates for thermoelectricmaterials due to the low thermal conductivities, were measured by a high-resolution Neutron powder
diffractometer Super-HRPD installed at the beam line BL08 of J-PARC facility. The powdered samples of tI- andhP-Na2In2Sn4 (dimorphs) and Na2+xAl2+xSn4−x (x = −0.18), 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 in a temperature range of 13–300 K for each sample
in order to get information on the atomic displacement parameters (ADPs) for Na atom, of which the static and/ordynamic positional disorders probably play an important role in the reduction of lattice thermal conductivity ofthe compounds. The crystal structures varying temperature were mainly analyzed using a Rietveld analysis
program, Z-Rietveld (ver. 1.0).

12. 実験方法及び結果（つづき） Experimental method and results (continued)
Results: The measured Neutron diffraction patterns of Na2+xAl2+xSn4-x (x= −0.18) and hP-Na2ZnSn5 wereexplained well by reported crystal structures having tunnel framework formed by Al/Sn or Zn/Sn atoms with ahexagonal cell [1, 2] in the whole measured temperature range (13–280 K), respectively. Although the diffraction
patterns of tI-Na2ZnSn5 from 300 K to 220 K were also identical with the ones reported tetragonal structure witha space group of 𝐼4#2𝑑 [2], some additional peaks were appeared in the patterns below 220 K and the peakintensities were gradually increased with decreasing temperature as shown in Fig. 1. This observation strongly
suggests a structural phase transition of tI-Na2ZnSn5.
In order to solve the crystal structure of tI-Na2ZnSn5 in the lower temperature range, single-crystal X-ray
diffraction measurements were carried out in a temperature range of 90–300 K, because determination of thespace group for the low-temperature phase was unsuccessful from the powder diffraction data. The single-crystal
structure analysis revealed that a structural phase transition was occurred at 220 K in accompany with a changeof the space group from the tetragonal 𝐼4#2𝑑 (tI-Na2ZnSn5: high temperature phase) to an orthorhombic P212121(oP-Na2ZnSn5: low temperature phase).
The crystal structures of tI- and oP-Na2ZnSn5 refined from the Neutron powder diffraction patterns based on
the solved crystal structures by single-crystal X-ray diffraction were shown in Fig. 2.

¥The tunnel frameworkof oP-Na2ZnSn5 was slightly distorted in comparison to the framework of tI-Na2ZnSn5, resulting increase in thenumber of crystallographic sites of Na and Sn atoms. The site occupancies of the pairs of adjacent Na sites(Na1A/1B = 0.79/0.21, Na2A/2B=0.85/0.15) in the tunnel were significantly unequal at 200 K. The occupanciesof the higher occupied Na sites (Na1A and Na2A) were increased with decreasing temperature and reached close
to be approximately 1 at 90 K. This structural change can be considered as an order-disorder transition of the Na
atom which would play an important role in the reduction of lattice thermal conductivity of the tunnel compounds.
More detailed structural analysis focusing on atomic displacement parameters of Na atoms for tI-, oP-, and hPNa2ZnSn5 (trimorphs) and Na2+xAl2+xSn4−x (x = −0.18) are now in progress.

TL-Na2ZnSn5

References [1] M. Kanno, T. Yamada, H. Yamane, H. Nagai, Chem. Mater., 28, 601 (2016).

[2] S. Stegmaier, S. J. Kim, A. Henze, T. F. Fässler, J. Am. Chem. Soc. 135, 10654 (2013).
(a)(b)

Na
300 K

Na1A

Occ. 0.5

Sn2
Sn1280 K

Intensity (a.u.)

260 K

Occ. 0.79

Na1B

Occ. 0.21

Sn2
Sn1
Sn4
Sn5
Sn3

Na2A

240 K

Occ. 0.85

220 K

Zn

200 K

Na2B

Occ. 0.15

Zn

180 K
160 K
100 K
50 K
300 K for 2 h
280 K for 7 h

260 K for 1 h
13 K





3TOF / 10 µsec

Fig. 1. Neutron powder diffractions of tINa2ZnSn5 measured from 13 K to 300 K.

240 K for 1 h
220 K for 1 h200 K for 7 h
180 K for 1 h160 K for 1 h
100 K for 7 h050 K for 7 h013 K for 7 hFig. 2. Crystal structures of tI-Na2ZnSn5 refined at 280 K (a) and oPNa2ZnSn5 200 K (b).

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