The high thermoelectric performance of dopant-free, low-cost and eco-friendly p-type Zn_1−xSb (x = 0, 0.01, 0.03, and 0.06) is demonstrated by synergistically optimizing its electrical and thermal properties via Zn-vacancy engineering. Upon increasing Zn-vacancies in ZnSb, the bandgap is observed to reduce due to the formation of the impurity states above the valence band, which is theoretically validated using density functional theory (DFT). Remarkably, Zn vacancy-driven point defects significantly influence the hole concentration within the Zn_1−xSb samples. At 300 K, the hole concentration (n_H) is boosted from 3.6 × 10¹⁸ cm⁻³ (in ZnSb) to 3.4 × 10¹⁹ cm⁻³ for the Zn_0.94Sb sample, culminating in a marked enhancement in electrical conductivity (σ) from 1.80 × 10⁴ S m⁻¹ to 7.57 × 10⁴ S m⁻¹ for Zn_0.94Sb. Equally noteworthy is the substantial decrease in thermal conductivity (κ) observed in the Zn_0.94Sb sample at 673 K, plunging from 2.29 W m⁻¹ K⁻¹ (in ZnSb) to 1.41 W m⁻¹ K⁻¹. This decline in thermal conductivity is attributed to the effective phonon scattering arising from Zn-vacancy-assisted point defects, combined with the efficient coupling of optical and acoustic phonons and the characteristic low group velocity, evidenced by the theoretically calculated phonon dispersion curve. Overall, the high thermoelectric figure of merit, zT of ∼0.8 at 673 K, is achieved for the sample with a 6 mol% Zn deficiency. Furthermore, a maximum theoretical conversion efficiency of ∼7% is predicted at a temperature gradient of 625 K, showing high potential for use in practical devices for mid-temperature applications, and the present work features the effect of a reliable dopant-free approach in improving the overall zT of eco-friendly and low-cost ZnSb.

中文翻译：

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增加锌空位后 p 型 ZnSb 的高热电性能：实验和理论研究

通过锌空位协同优化其电学和热学性能，证明了无掺杂、低成本且环保的 p 型 Zn _{1− x} Sb ( x = 0、0.01、0.03 和 0.06)的高热电性能工程。当 ZnSb 中的锌空位增加时，由于价带上方杂质态的形成，观察到带隙减小，这一点使用密度泛函理论 (DFT) 得到了理论上的验证。值得注意的是，Zn 空位驱动的点缺陷显着影响 Zn _{1− x} Sb 样品内的空穴浓度。在 300 K 时， Zn _0.94 Sb 样品的空穴浓度 ( n _{H ) 从 3.6 × 10} ¹⁸ cm ^-3 （在 ZnSb 中）提高到 3.4 × 10 ¹⁹ cm ^-3，最终导致电导率 ( σ )显着增强。 )对于 Zn _0.94 Sb，从 1.80 × 10 ⁴ S m ^-1到 7.57 × 10 ⁴ S m ^-1 。同样值得注意的是Zn _0.94 Sb 样品在 673 K 时观察到热导率 ( κ )大幅下降，从 2.29 W m ^-1 K ^-1（在 ZnSb 中）骤降到 1.41 W m ^-1 K ^-1。热导率的下降归因于锌空位辅助点缺陷产生的有效声子散射，再加上光学和声学声子的有效耦合以及低群速度的特征，理论计算的声子色散曲线证明了这一点。总体而言，缺锌量为 6 mol% 的样品在 673 K 时实现了高热电品质因数，zT约为 0.8。此外，在 625 K 的温度梯度下预计最大理论转换效率为 ∼7%，显示出在中温应用的实际器件中的巨大潜力，并且目前的工作特点是可靠的无掺杂方法在提高环保且低成本的ZnSb的整体zT 。