Pressure-induced enhancement of thermoelectric power factor in pristine and hole-doped SnSe crystals

Na Su; B C Qin; K J Zhu; Z Y Liu; P Shahi; J P Sun; B S Wang; Y Sui; Y G Shi; L D Zhao; J-G Cheng

doi:10.1039/c9ra05134a

Pressure-induced enhancement of thermoelectric power factor in pristine and hole-doped SnSe crystals

RSC Adv. 2019 Aug 28;9(46):26831-26837. doi: 10.1039/c9ra05134a. eCollection 2019 Aug 23.

Authors

Na Su^{1

2}, B C Qin³, K J Zhu^{1

2}, Z Y Liu^{1

4}, P Shahi^{1

5}, J P Sun¹, B S Wang^{1

2

6}, Y Sui⁴, Y G Shi^{1

2

6}, L D Zhao³, J-G Cheng^{1

2

6}

Affiliations

¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing 100190 China jgcheng@iphy.ac.cn.
² School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100190 China.
³ School of Materials Science and Engineering, Beihang University Beijing 100191 China.
⁴ School of Physics, Harbin Institute of Technology Harbin 15001 China.
⁵ Department of Physics, D. D. U. Gorakhpur University Gorakhpur-273009 India.
⁶ Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China.

Abstract

We evaluate the influence of pressure on the thermoelectric power factors PF ≡ S ² σ of pristine and Na-doped SnSe crystals by measuring their electrical conductivity σ(T) and Seebeck coefficient S(T) up to ∼22 kbar with a self-clamped piston-cylinder cell. For both cases, σ(T) is enhanced while S(T) reduced with increasing pressure as expected, but their imbalanced variations lead to a monotonic enhancement of PF under pressure. For pristine SnSe, σ(290 K) increases by ∼4 times from ∼10.1 to 38 S cm^-1, while S(290 K) decreases by only ∼12% from 474 to 415 μV K^-1, leading to about three-fold enhancement of PF from 2.24 to 6.61 μW cm^-1 K^-2, which is very close to the optimal value of SnSe above the structural transition at ∼800 K at ambient pressure. In comparison, the PF of Na-doped SnSe at 290 K is enhanced moderately by ∼30% up to 20 kbar. In contrast, the PF of isostructural black phosphorus with a simple band structure was found to decrease under pressure. The comparison with black phosphorus indicates that the multi-valley valence band structure of SnSe is beneficial for the enhancement of PF by retaining a large Seebeck coefficient under pressure. Our results also provide experimental confirmation on the previous theoretical prediction that high pressure can be used to optimize the thermoelectric efficiency of SnSe.