The recent dramatic improvements in high-performance thermoelectric (TE) oxides provide new exciting applications in the TE field, but the mechanical properties so important for engineering applications remain largely unexplored. Based on density functional theory (DFT) calculations, we report the ideal strength, deformation mechanism, and fracture toughness of such TE oxides as n-type ZnO and SrTiO_3 and p-type BiCuSeO and NaCo_2O_4. The Zn-O and Ti-O bonds forming the 3D Zn-O and Ti-O frameworks dominate the deformation and failure mechanisms of ZnO and SrTiO_3, respectively. Due to the higher stiffness of Ti-O octahedra compared with that of Zn-O tetrahedra, SrTiO_3 exhibits more robust macro-mechanical properties such as elastic modulus and fracture toughness than ZnO. The Bi-Se and Na-O bonds, which couple the different 2D substructures, are responsible for the relative slip in BiCuSeO and NaCo_2O_4, respectively. Since the Zn-O and Ti-O bonds are much stronger than the Bi-Se and Na-O bonds, we find that n-type ZnO and SrTiO_3 have a higher ideal strength and fracture toughness compared with p-type BiCuSeO and NaCo_2O_4. This work reveals that for TE module applications of oxides, it is most important to significantly improve the mechanical properties of the p-leg.

中文翻译：

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热电氧化物的机械性能：理想的强度、变形机制和断裂韧性

高性能热电 (TE) 氧化物最近的显着改进在 TE 领域提供了令人兴奋的新应用，但对于工程应用如此重要的机械性能在很大程度上仍未得到探索。基于密度泛函理论 (DFT) 计算，我们报告了诸如 n 型 ZnO 和 SrTiO_3 以及 p 型 BiCuSeO 和 NaCo_2O_4 等 TE 氧化物的理想强度、变形机制和断裂韧性。形成3D Zn-O和Ti-O骨架的Zn-O和Ti-O键分别主导了ZnO和SrTiO_3的变形和破坏机制。由于 Ti-O 八面体的刚度比 Zn-O 四面体更高，SrTiO_3 表现出比 ZnO 更强大的宏观力学性能，如弹性模量和断裂韧性。Bi-Se 和 Na-O 键，耦合不同的 2D 子结构，分别导致 BiCuSeO 和 NaCo_2O_4 的相对滑移。由于Zn-O 和Ti-O 键比Bi-Se 和Na-O 键强得多，我们发现n 型ZnO 和SrTiO_3 与p 型BiCuSeO 和NaCo_2O_4 相比具有更高的理想强度和断裂韧性。这项工作表明，对于氧化物的 TE 模块应用，最重要的是显着改善 p 腿的机械性能。