Grain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction
Xiyang Li(李西阳)1,2, Zhigang Zhang(张志刚)1,3, Lunhua He(何伦华)1,3, Maxim Avdeev4, Yang Ren(任洋)5, Huaizhou Zhao(赵怀周)1, and Fangwei Wang(王芳卫)1,2,3,†
1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 2School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 101408, China 3Songshan Lake Materials Laboratory, Dongguan 523808, China 4Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia 5X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99.
* Project supported by the National Natural Science Foundation of China (Grant No. 11675255) and the National Key R&D Program of China (Grant No. 2016YFA0401503).
Cite this article:
Xiyang Li(李西阳), Zhigang Zhang(张志刚), Lunhua He(何伦华), Maxim Avdeev, Yang Ren(任洋), Huaizhou Zhao(赵怀周), and Fangwei Wang(王芳卫)† Grain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction 2020 Chin. Phys. B 29 106101
Fig. 1.
(a) Crystalline structure of α-MgAgSb, the space group is I-4c2 (No. 120). (b) The neutron diffraction, and synchrotron x-ray diffraction data of MgAg0.97Sb0.99 measured at room temperature.
Fig. 2.
Rietveld refinement of MgAg0.97Sb0.99 neutron diffraction data with size parameter refined (a), and without size parameter refined (b).
Neutron diffraction
X-ray diffraction
Cell parameters:
a, b/Å
9.1706(7)
9.1723(3)
c/Å
12.7082(9)
12.7100(4)
V/Å3
1068.8(2)
1069.1(2)
Atom parameters:
Mg
x
−0.0232(4)
−0.030(2)
y
0.2837(4)
0.284(2)
z
0.1101(3)
0.1128(9)
Ag1
x
{0}
{0}
y
0
0
z
0.25
0.25
Ag2
x
0
0
y
0
0
z
0
0
Ag3
x
0.2239(3)
0.2243(4)
y
0.2239(3)
0.2243(4)
z
0.25
0.25
Sb
x
0.2353(4)
0.2357(3)
y
0.4751(4)
0.4767(3)
z
0.1180(3)
0.1172(2)
Mg–Sb bond distances:
b1/Å
2.937(5)
2.97(2)
b2/Å
2.948(4)
2.90(2)
b3/Å
2.952(4)
3.02(2)
b4/Å
3.247(4)
3.21(2)
b5/Å
3.460(5)
3.44(2)
b6/Å
3.871(4)
3.90(2)
Mg-Sb bond angles:
b1–b2/(°)
100.2(3)
99.9(3)
b1–b3/(°)
87.0(2)
85.4(3)
b1–b4/(°)
95.2(2)
94.8(3)
b1–b6/(°)
83.1(2)
81.7(3)
b2–b3/(°)
94.7(2)
94.6(3)
b2–b4/(°)
95.6(2)
97.5(3)
b2–b5/(°)
90.0(2)
91.8(3)
b3–b5/(°)
90.0(2)
89.8(3)
b3–b6/(°)
83.5(2)
82.1(3)
b4–b5/(°)
86.0(2)
87.5(3)
b4–b6/(°)
86.0(2)
85.8(3)
b5–b6/(°)
86.6(2)
86.3(2)
X and Y parameters:
X/(°)
–
0.36431
Y/(°)
0.184(6)
0.0012(2)
Size parameters:
GausSiz/(°)2
0.008(2)
0.000617(3)
Grain size/nm
28(4)
24(1)
Reliability factorsa:
Rwp/%
10.8
9.94
χ2
1.98
10.2
Table 1.
Refined parameters of MgAg0.97Sb0.99 measured by high resolution neutron diffraction and synchrotron x-ray diffraction, respectively.
Fig. 3.
Rietveld refinement of MgAg0.97Sb0.99 synchrotron x-ray diffraction data with size parameter refined (a), and without size parameter refined (b).
Fig. 4.
Static structure distortion in MgAg0.97Sb0.99. The refined bond distances and bond angles of the nearest Mg–Sb bonds are shown in Table 1. The refinement results show a significant distortion of this Mg–Sb formed distorted NaCl structure.
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