Huang Yang, Fu Tairan, Xu Xuefei, Wang Na
Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Beijing Key Laboratory of CO2 Utilization and Reduction Technology, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, People's Republic of China.
Center for Combustion Energy, Department of Energy and Power Engineering, and Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, People's Republic of China.
J Phys Condens Matter. 2021 Sep 6;33(46). doi: 10.1088/1361-648X/ac1ec7.
MoSiis widely concerned due to excellent electrical conductivity, oxidation resistance as a typical transition metal silicide. The high-temperature diffusion behavior is one of the important factors for the degradation of MoSicoatings. However, the diffusion mechanism in MoSiis still unclear. Prior theoretical work mostly focused on defect formation energy, but these are not consistent with the self-diffusion experiments because the migration behaviors were not considered. Therefore, the purpose of this work was to investigate the microscopic diffusion mechanisms of Mo and Si atoms in MoSiusing density functional theory and the CI-NEB method. We confirmed that the temperature-dependent vibrational contribution has a significant impact on the defect formation free energy. The isolated point defects in MoSiwill tend to aggregate to form defect complexes, which participate in the atomic diffusion as mediators. The defect migration behaviors of atoms for vacancy mediated, vacancy complex mediated, and antisite assisted jumps were obtained based on electronic structures analysis. The results show that Si diffusion is mediated by intrasublattice jumps of the nearest neighbor Si vacancies. Moreover, the destroyed covalent Mo-Si bonds by Si vacancies and the non-directional weak metal bonds formed by the Mo antisites and Mo atoms could improve the mobility of the Mo atom which results in the low migration barrier. The agreement between our calculations and the reported experimental results indicates that the dominant diffusion mechanism for Mo atoms is mediated by vacancy complex mediated jumps and antisite assisted jumps. It is concluded that the Si vacancy-based defect complexes are likely the diffusion mediators for Mo atom self-diffusion in MoSi. This work provides a deeper insight into the connection between the atomic mechanism and the macroscopic behavior for the diffusion in the MoSi, and establishes the basis for further optimizing high-temperature coating materials.
作为一种典型的过渡金属硅化物，MoSi由于其优异的导电性和抗氧化性而受到广泛关注。高温扩散行为是MoSi涂层退化的重要因素之一。然而，MoSi中的扩散机制仍不清楚。先前的理论工作大多集中在缺陷形成能上，但这些与自扩散实验不一致，因为没有考虑迁移行为。因此，这项工作的目的是使用密度泛函理论和CI-NEB方法研究MoSi中Mo和Si原子的微观扩散机制。我们证实了温度依赖的振动贡献对缺陷形成自由能有显著影响。MoSi中的孤立点缺陷倾向于聚集形成缺陷复合体，这些复合体作为介质参与原子扩散。基于电子结构分析，获得了空位介导、空位复合体介导和反位辅助跳跃的原子缺陷迁移行为。结果表明，Si扩散是由最近邻Si空位的亚晶格内跳跃介导的。此外，Si空位破坏的共价Mo-Si键以及Mo反位与Mo原子形成的无方向性弱金属键可以提高Mo原子的迁移率，从而导致低迁移势垒。我们的计算结果与报道的实验结果之间的一致性表明，Mo原子的主要扩散机制是由空位复合体介导的跳跃和反位辅助跳跃介导的。得出的结论是，基于Si空位的缺陷复合体可能是MoSi中Mo原子自扩散的扩散介质。这项工作为深入了解MoSi中扩散的原子机制与宏观行为之间的联系提供了帮助，并为进一步优化高温涂层材料奠定了基础。
