华中科技大学杨君友团队报道了二维Bi2Si2Te6半导体的热电性能。相关研究成果发表在2022年1月14日出版的《美国化学会杂志》。

二维化合物Bi2Si2Te6是一种直接带隙半导体，其光学带隙约为0.25eV，是一种很有前途的热电材料。采用可分级球磨和退火工艺制备了单相Bi2Si2Te6，并采用火花等离子体烧结法制备了高密度的多晶样品。Bi2Si2Te6表现出p型半导体输运行为，在573 K时表现出约0.48 W m^–1 K^–1（交叉面）的固有低晶格热导率。

第一性原理密度泛函理论计算表明，该低晶格热导率源自声子与晶体之间的相互作用。Bi2Si2Te6独特的二维晶体结构和介价键导致了低能光学声子、Bi的局域振动、低德拜温度和强非谐性。Bi2Si2Te6在623 K时表现出最佳的ZT值为～0.51，可通过用Pb替代Bi进一步增强。由于载流子浓度的增加，在773 K时,Pb掺杂导致功率因数S2σ大幅增加，从Bi2Si2Te6的～3.9μW cm^–1 K^–2增加到Bi198Pb0.02Si2Te6的～8.0μW cm^–1 K^–2。

此外，由于强化点缺陷（PbBi′）散射,在Bi1.98Pb0.02Si2Te6中，Pb掺杂导致晶格热导率在623K时进一步降低至～0.38W m^–1K^–1（交叉面）。同时优化功率因数和晶格，Bi1.98Pb0.02Si2Te6热导率在723K时达到峰值ZT约为0.90，在400–773K时，的平均ZT约为0.66。

附：英文原文

Title: Thermoelectric Performance of the 2D Bi2Si2Te6 Semiconductor

Author: Yubo Luo, Zheng Ma, Shiqiang Hao, Songting Cai, Zhong-Zhen Luo, Christopher Wolverton, Vinayak P. Dravid, Junyou Yang, Qingyu Yan, Mercouri G. Kanatzidis

Issue&Volume: January 14, 2022

Abstract: Bi2Si2Te6, a 2D compound, is a direct band gap semiconductor with an optical band gap of ～0.25 eV, and is a promising thermoelectric material. Single-phase Bi2Si2Te6 is prepared by a scalable ball-milling and annealing process, and the highly densified polycrystalline samples are prepared by spark plasma sintering. Bi2Si2Te6 shows a p-type semiconductor transport behavior and exhibits an intrinsically low lattice thermal conductivity of ～0.48 W m–1 K–1 (cross-plane) at 573 K. The first-principles density functional theory calculations indicate that such low lattice thermal conductivity is derived from the interactions between acoustic phonons and low-lying optical phonons, local vibrations of Bi, the low Debye temperature, and strong anharmonicity result from the unique 2D crystal structure and metavalent bonding of Bi2Si2Te6. The Bi2Si2Te6 exhibits an optimal figure of merit ZT of ～0.51 at 623 K, which can be further enhanced by the substitution of Bi with Pb. Pb doping leads to a large increase in power factor S2σ, from ～3.9 μW cm–1 K–2 of Bi2Si2Te6 to ～8.0 μW cm–1 K–2 of Bi1.98Pb0.02Si2Te6 at 773 K, owing to the increase in carrier concentration. Moreover, Pb doping induces a further reduction in the lattice thermal conductivity to ～0.38 W m–1 K–1 (cross-plane) at 623 K in Bi1.98Pb0.02Si2Te6, due to strengthened point defect (PbBi′) scattering. The simultaneous optimization of the power factor and lattice thermal conductivity achieves a peak ZT of ～0.90 at 723 K and a high average ZT of ～0.66 at 400–773 K in Bi1.98Pb0.02Si2Te6.

DOI: 10.1021/jacs.1c12507

Source: https://pubs.acs.org/doi/10.1021/jacs.1c12507