In this study, a series of Bi₂Te_2-xS_1+x compounds were prepared by traditional melting-quenching-annealing process. In the range of 0.03 ≤ x ≤ 0.25, Bi₂Te_2-xS_1+x compounds possess the Bi₂Te₃ structure. S atoms preferentially fully occupy the Te⁽²⁾ sites, while any extra S atoms randomly occupy the Te⁽¹⁾ sites. Experimental results and phonon dispersion calculations demonstrate that the strong coupling of the phonon density of state contributed by Bi and Te⁽¹⁾ atoms results in the low avoided-crossing frequencies, sound velocities, Debye temperature and therefore the low lattice thermal conductivities. Moreover, substitutions of extra S atoms on the Te⁽¹⁾ site intensifies alloy phonon scattering that further suppresses the lattice thermal conductivity. An ultra-low lattice thermal conductivity of 0.49 W m⁻¹ K⁻¹ is achieved at 523 K. Doping with Cl increases the room temperature carrier concentration, resulting in a significantly enhanced power factor from 1.5 mW m⁻¹ K⁻² for the Bi₂Te_1.93S_1.07 sample to 1.7 mW m⁻¹ K⁻² for the Cl-doped sample at 323 K. Furthermore, doping with Cl enhances phonon point defect scattering that leads to a suppression of the thermal conductivity to 0.41 W m⁻¹ K⁻¹ at 573 K. As a result of the optimization of the electronic transport properties and the reduction in the lattice thermal conductivity, Bi₂Te_1.93S_1.065Cl_0.005 sample achieved the highest ZT of 0.67 at 623 K which is superior to intrinsic Bi₂Te₃ in the whole temperature range.

本研究采用传统的熔融-淬火-退火工艺制备了一系列Bi ₂ Te _2-x S _1+x化合物。在0.03≤x≤0.25的范围内，Bi ₂ Te _2-x S _1+x化合物具有Bi ₂ Te ₃结构。S 原子优先完全占据 Te ⁽²⁾位点，而任何额外的 S 原子随机占据 Te ⁽¹⁾位点。实验结果和声子色散计算表明 Bi 和 Te 贡献的声子态密度的强耦合⁽¹⁾原子导致低避免交叉频率、声速、德拜温度，因此导致低晶格热导率。此外，Te ⁽¹⁾位点上额外的 S 原子的取代加强了合金声子散射，进一步抑制了晶格热导率。在 523 K 下实现了 0.49 W m ^-1  K ^-1的超低晶格热导率。 掺杂 Cl 增加了室温载流子浓度，导致功率因数从 1.5 mW m ^-1  K ^-2显着提高，用于比₂特_{1 ．93} S _1.07样品至 1.7 mW m ^-1  K ^-2对于 323 K 下的 Cl 掺杂样品。此外，掺杂 Cl 增强了声子点缺陷散射，导致热导率在 573 K下被抑制到 0.41 W m ^-1  K ^-1。作为优化的结果电子传输特性和晶格热导率的降低，Bi ₂ Te _{1 。93}秒_{1 . 065} Cl _0.005样品在 623 K 下达到了0.67的最高ZT，在整个温度范围内均优于本征 Bi ₂ Te ₃。