Center for Nanomaterials Characterization, Korea Research Institute of Standards and Science, Daejeon, 305-340, Republic of Korea.
Nanoscale. 2014 Jun 7;6(11):6158-65. doi: 10.1039/c4nr00191e. Epub 2014 May 2.
Thermoelectric figure-of-merits (ZT) are enhanced or degraded by crystal defects such as twins and excess atoms that are correlated with thermal conductivity (k) and carrier concentration (n). For Bi2Te3, it is unclear whether the crystal defects can enhance ZT without a degradation in the thermopower factor. In the present study, n-type Bi2Te3 nanowires (NWs) are electrochemically synthesized to have twin-free (TF) or twin-containing (TC) microstructures with a ZT of 0.10 and 0.08, respectively, at 300 K. The ZTs of TF and TC NWs remarkably increase up to 0.21 and 0.31, when heat-treatments cause n-reduction and twins induce phonon scattering, as follows: first, the enhancement of the Seebeck coefficient from -70 to -98 μV K(-1) for TF NWs and from -57 to -143 μV K(-1) for TC NWs, by virtue of n-reduction; secondly, twin-driven k-reduction from 1.9 to 1.4 W m(-1) K(-1) of TC NWs, while the k of TF NWs increases from 2.3 to 2.6 W m(-1) K(-1) due to the enhanced carrier mobility. The lattice thermal conductivities of TC NW are lowered from 1.1 to 0.8 W m(-1) K(-1) by phonon scattering at twins. Density functional theory calculations indicate that twins do not significantly influence the Seebeck coefficient of Bi2Te3. It is strongly recommended that twins be incorporated with an optimum carrier concentration to enhance the ZT of Bi2Te3.
热电优值（ZT）可通过与热导率（k）和载流子浓度（n）相关的晶体缺陷（如孪晶和过剩原子）得到增强或降低。对于 Bi2Te3，晶体缺陷是否可以在不降低热功率因子的情况下增强 ZT 尚不清楚。在本研究中，通过电化学合成 n 型 Bi2Te3 纳米线（NWs），使其具有无孪晶（TF）或含孪晶（TC）的微观结构，在 300 K 时的 ZT 值分别为 0.10 和 0.08。当热处理导致 n 减少和孪晶诱导声子散射时，TF 和 TC NWs 的 ZT 值显著增加至 0.21 和 0.31，如下所示：首先，通过 n 减少，TF NWs 的 Seebeck 系数从-70 增加到-98 μV K(-1)，TC NWs 的 Seebeck 系数从-57 增加到-143 μV K(-1)；其次，孪晶驱动的 k 减少，TC NWs 的 k 从 1.9 减少到 1.4 W m(-1) K(-1)，而 TF NWs 的 k 由于载流子迁移率的提高而从 2.3 增加到 2.6 W m(-1) K(-1)。孪晶散射使 TC NW 的晶格热导率从 1.1 降低到 0.8 W m(-1) K(-1)。密度泛函理论计算表明，孪晶对 Bi2Te3 的 Seebeck 系数没有显著影响。强烈建议将孪晶与最佳载流子浓度结合使用，以提高 Bi2Te3 的 ZT。
