Supporting Information for
Optimization of thermoelectric performance on the anisotropic AgxSn1-xSe compounds
Huaqian Lenga,b, Min Zhoua,*, Jie Zhaoa,b, Yemao Hana,b, Laifeng Lia,*
a
State Key Laboratory of Technologies in Space Cryogenic Propellants, Technical Institute of
Physics and Chemistry, Chinese Academy of Sciences, Beijing, China
b
University of Chinese Academy of Sciences, Beijing, China
* Corresponding Authors:
Min Zhou mzhou@mail.ipc.ac.cn Laifeng Li laifengli@mail.ipc.ac.cn
1. The experimental results and theoretical method of indirect-bandgap calculations.
Figure 1 (a) UV-Vis-NIR spectrum of the AgxSn1-xSe sample at 300 K. (b) (ah) 0.5 – h plot of AgxSn1-xSe
If we assume for simplicity k=0 allowed transitions, the primary optical transition has been shown
that near the band edge the optical absorption has the following behavior1:
A
(h  Eg )
n
2
h
Where A is a constant and n depends on whether the transition is direct (n = 1) or indirect (n = 4).
Both low temperature phases and high temperature phase of SnSe are indirect-bandgap (Eg)
compounds. For the low temperature phase, the indirect bandgap is along ΓY in its Brillouin zones;
for the high temperature phase, the indirect bandgap is from a point within the ΓP direction to the Z
point in its Brillouin zones2. As a result of indirect-bandgap transition, n is given 4. The band gap
of the undoped SnSe was determined to be 0.59eV, which is roughly consistent with other reports2,3.
With the Na-content increasing in SnSe, the band gap of the AgxSn1-xSe shows decreasing trends.
2. The thermal stability of the polycrystalline materials and the thermal degradation of
transport properties.
Figure 2 Comparison of electrical (a) and thermal (c) transport properties for the same Ag-alloyed SnSe samples
between two measurements, and the solid (dashed) curve corresponds to the first (second) measurements
perpendicular to the pressing direction. The thermal degradation of electrical (b) and thermal (d) transport properties.
The decay rate (D) could be calculated from the relationship:
D  ( M1  M 2 ) / M1
Where M1 and M2 is the first and second measurement respectively of electrical or thermal
transport properties.
3. Thermal conductivity of the Pnma phase of SnSe: comparison between experimental results
for monocrystals2 and polycrystals4,5.
Figure 3 Thermal conductivity of the Pnma phase of SnSe: comparison between experimental results for
monocrystals2 and polycrystals4,5. For polycrystalline samples, the lower (higher) curve corresponds to
measurements parallel (perpendicular) to the pressing direction.
References
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L. D. Zhao, S. H. Lo, Y. Zhang, H. Sun, G. Tan, C. Uher, C. Wolverton, V. P. Dravid, and M. G.
Kanatzidis, Nature 508, 373 (2014).
3.
S. Bhattacharya, A. L. Pope, R. T. Littleton, T. M. Tritt, V. Ponnambalam, Y. Xia, and S. J. Poon,
Applied Physics Letters 77, 2476 (2000).
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S. Sassi, C. Candolfi, J. B. Vaney, V. Ohorodniichuk, P. Masschelein, A. Dauscher, and B. Lenoir,
Applied Physics Letters 104 (2014).
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C.-L. Chen, H. Wang, Y.-Y. Chen, T. Day, and G. J. Snyder, Journal of Materials Chemistry A 2,
11171 (2014).