Su Na, Qin B C, Zhu K J, Liu Z Y, Shahi P, Sun J P, Wang B S, Sui Y, Shi Y G, Zhao L D, Cheng J-G
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100190 China.
RSC Adv. 2019 Aug 28;9(46):26831-26837. doi: 10.1039/c9ra05134a. eCollection 2019 Aug 23.
We evaluate the influence of pressure on the thermoelectric power factors PF ≡ of pristine and Na-doped SnSe crystals by measuring their electrical conductivity () and Seebeck coefficient () up to ∼22 kbar with a self-clamped piston-cylinder cell. For both cases, () is enhanced while () reduced with increasing pressure as expected, but their imbalanced variations lead to a monotonic enhancement of PF under pressure. For pristine SnSe, (290 K) increases by ∼4 times from ∼10.1 to 38 S cm, while (290 K) decreases by only ∼12% from 474 to 415 μV K, leading to about three-fold enhancement of PF from 2.24 to 6.61 μW cm K, 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.
我们通过使用自夹紧活塞 - 圆筒装置测量原始和钠掺杂的SnSe晶体在高达约22千巴压力下的电导率（σ）和塞贝克系数（S），来评估压力对其热电功率因子PF≡σS²的影响。在这两种情况下，正如预期的那样，随着压力增加，σ增大而S减小，但它们变化的不平衡导致压力下PF单调增强。对于原始SnSe，σ（290K）从约10.1 S cm增大约4倍至38 S cm，而S（290K）仅从474 μV K减小约12%至415 μV K，导致PF从2.24 μW cm⁻¹K⁻²增大约三倍至6.61 μW cm⁻¹K⁻²，这非常接近室温下约800K结构转变以上SnSe的最佳值。相比之下，钠掺杂的SnSe在290K时，PF在高达20千巴的压力下适度增强约30%。相反，具有简单能带结构的同构黑磷的PF在压力下被发现会降低。与黑磷的比较表明，SnSe的多谷价带结构有利于在压力下通过保持较大的塞贝克系数来增强PF。我们的结果也为之前的理论预测提供了实验证实，即高压可用于优化SnSe的热电效率。
