Huang Jilong, Yan Peng, Liu Yongping, Xing Juanjuan, Gu Hui, Fan Yuchi, Jiang Wan
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China.
Institute of Functional Materials, Donghua University, Shanghai 201620, China.
ACS Appl Mater Interfaces. 2020 Nov 25;12(47):52721-52730. doi: 10.1021/acsami.0c16084. Epub 2020 Nov 12.
The low powder factor (PF) of polycrystalline oxide perovskites induced by the resistive grain boundaries or known as double Schottky barrier (DSB) greatly restricts their thermoelectric performance in application. Here, a general protocol including (i) powder and (ii) bulk reduction in H/Ar forming gas is demonstrated to break the DSB in La and Nb codoped SrTiO. While the powder reduction guarantees a high carrier concentration by fully stimulating the donor doping effect, the bulk reduction effectively lowers the DSB by influencing the point defects at grain boundaries, which is proved by the combination of cathode luminescence spectra and energy-dispersive X-ray spectroscopy in transmission electron microscopy. The Hall mobility can approach 10 cm V s after two-step reduction, which is similar to the level of single crystals. However, the Seebeck coefficient is not compromised, giving rise to high PF values up to 1.70 mW m K under proper reduction strength. Meanwhile, the reduction process also promotes mild precipitation of Nb nanoparticles, thus effectively lowering the lattice thermal conductivity by scattering phonons. As a result, a remarkable figure of merit reaching 0.4 at 700 K is obtained, which validates the two-step reduction as a reliable strategy toward "electron crystal-phonon glass" behavior in SrTiO-based perovskites.
由电阻性晶界引起的多晶氧化物钙钛矿的低粉末因子（PF），即所谓的双肖特基势垒（DSB），极大地限制了它们在应用中的热电性能。在此，展示了一种通用方法，包括（i）在H/Ar形成气体中进行粉末还原和（ii）块体还原，以打破La和Nb共掺杂的SrTiO₃中的DSB。虽然粉末还原通过充分激发施主掺杂效应保证了高载流子浓度，但块体还原通过影响晶界处的点缺陷有效地降低了DSB，这通过透射电子显微镜中的阴极发光光谱和能量色散X射线光谱相结合得到了证明。经过两步还原后，霍尔迁移率可接近10 cm² V⁻¹ s⁻¹，与单晶水平相当。然而，塞贝克系数并未受到影响，在适当的还原强度下，产生了高达1.70 mW m⁻¹ K⁻²的高PF值。同时，还原过程还促进了Nb纳米颗粒的轻度沉淀，从而通过散射声子有效地降低了晶格热导率。结果，在700 K时获得了高达0.4的显著优值，这验证了两步还原是在基于SrTiO₃的钙钛矿中实现“电子晶体 - 声子玻璃”行为的可靠策略。
