Remarkable Improvement of Thermoelectric Figure-of-Merit in SnTe through In Situ-Created Te Nanoinclusions
Remarkable Improvement of Thermoelectric Figure-of-Merit in SnTe through In Situ-Created Te Nanoinclusions
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DOI：
10.1021/acsaem.0c01156
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发表时间：
2020-07-27
影响因子：
6.4
通讯作者：
Aswal, D. K.
中科院分区：
文献类型：
--
作者：
Ahmad, Sajid;Singh, Ajay;Aswal, D. K.
由于本征Sn空位导致的非常高的空穴浓度，SnTe表现出非常低的塞贝克系数沿着高的电-热传导率。所有这些不利的热电参数限制了原始SnTe成为优秀的热电材料。在这项工作中，我们证明了通过在SnTe矩阵中原位创建Te纳米夹杂物的SnTe的品质因数的改善。为了合成SnTe，我们有意在化学计量的Sn/Te（1：1）中添加过量的Te。在SnTe从熔体凝固期间，液态的过量Te被排出到晶界。在进一步冷却时，当Te开始固化时，它在已经固化的SnTe晶粒中施加应变，并产生广泛的结构缺陷，包括位错、孪晶界和亚晶界，这些缺陷散射中波长的声子。由于本征Sn空位和SnTe/Te晶界引起的点缺陷分别散射低波长和高波长的声子。整个光谱的声子通过分层缺陷的有效散射引起的超低晶格热导率为0.5 W m（-1）K-1，接近理论最低限度。重空穴价带在输运中的贡献沿着SnTe/Te界面载流子的能量过滤导致室温附近Seebeck系数的改善。改进的塞贝克系数和抑制的热导率的累积效应引起高的品质因数（ZT）值，其在750 K下类似于1.5，并且Sn 0.9Te样品的平均ZT类似于0.48。
SnTe exhibits very low Seebeck coefficient along with high electrical-thermal conductivities owing to very high hole concentration that results from intrinsic Sn vacancies. All these unfavorable thermoelectric parameters restrict pristine SnTe from becoming an outstanding thermoelectric material. In this work, we demonstrate the improvement in figure-of-merit of SnTe through in situ creation of Te nanoinclusions in the SnTe matrix. We have intentionally added excess Te in stoichiometric Sn/Te (1:1) for the synthesis of SnTe. During solidification of SnTe from the melt, the excess Te in the liquid state gets expelled to the grain boundaries. On further cooling, when Te starts to solidify, it exerts strain in the already solidified SnTe grains and creates extensive structural defects including dislocations, twin boundaries, and subgrain boundaries that scatter phonons of midwavelength. The point defect due to intrinsic Sn vacancies and SnTe/Te grain boundaries respectively scatters phonons of low and high wavelengths. Effective scattering of the entire spectrum of phonons through the hierarchical defects gives rise to an ultralow lattice thermal conductivity of 0.5 W m(-1) K-1 that is close to the theoretical minimum limit. The contribution from the heavy hole valence band in transport along with energy filtering of charge carriers at the SnTe/Te interface results in improvement of the Seebeck coefficient near room temperature. The cumulative effect of improved Seebeck coefficient and suppressed thermal conductivity gives rise to a high figure-of-merit (ZT) value of similar to 1.5 at 750 K and an average ZT of similar to 0.48 for the Sn0.9Te sample.