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Influence of Nonstoichiometry on Thermoelectric Properties of Single Crystalline SnSe

Authors: Šraitrová Kateřina | Kucek Vladimír | Drašar Čestmír

Year: 2018

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
cze	Influence of Nonstoichiometry on Thermoelectric Properties of Single Crystalline SnSe	Recently, high thermoelectric performance (ZT = 2.6 at 923 K) has been reported in single crystal SnSe [1]. SnSe crystalizes in a complex structure Pnma space group with orthorhombic symmetry. Above 810 K this structure changes to Cmcm space group [2,3]. Native defects play very important role in thermoelectric properties of SnSe. Most likely, Sn vacancies are responsible for rapid increment of the carrier concentration and electrical conductivity with temperature at T > 600 K [4]. Another native defects are Se interstitials. Their large concentration seems to be responsible for extremely low thermal conductivity of SnSe [5]. In order to clarify the role of nonstoichiometry and solubility of Sn in SnSe structure, nonstoichiometric single crystals were prepared. Namely SnSe1+x, where x = - 0.02, - 0.01, 0, 0.01 and 0.02. The samples were characterized by X-ray diffraction, electrical conductivity, Hall coefficient and Seebeck coefficient. These parameters were measured over a temperature range of 93 - 473 K. Concentration of free charge carriers and their mobility were calculated from obtained data. From X-ray diffraction analysis it follows that samples with overstoichiometry of Se contain foreign phase SnSe2. Generally, overstoichiometry of Se leads to higher values of electrical conductivity in comparison with understoichiometric samples. At low temperatures electrical conductivity vary with stoichiometry significantly from 8600 Ω-1m-1 for x = 0 to 2700 Ω-1m-1 for x = - 0.01 at 100 K. Values of Hall coefficient are quite high (~ 20 cm3C-1), but almost identical for all of the samples except for x = -0.01. This sample reaches values ~ 40 cm3C-1. Sample with x = - 0.02 reaches highest values of concentration of free charge carriers (~ 5x1017 cm-3). On the contrary, sample with x = - 0.01 reaches lowest values (~ 1.5x1017 cm-3) suggesting a very low concentration of defects. It seems that any larger Se understoichiometry is not allowed at SnSe and redundant tin is ex