Guo Jing, Feng Yunli, Tang Cong, Wang Li, Qing Xiaoliang, Yang Qingxiang, Ren Xuejun
School of Engineering, Faculty of Engineering and Technology, Liverpool John Moores University, Liverpool L3 3AF, UK.
Hebei Key Laboratory of Modern Metallurgy Technology, College of Metallurgy and Energy, North China University of Science and Technology, Tangshan 063009, China.
Materials (Basel). 2022 Jul 5;15(13):4719. doi: 10.3390/ma15134719.
In this paper, first principles method was adopted to investigate the point defects, Vanadium-related defects and defect combinations (vacancy (V), substitutional (S) and/or interstitial (I)) in molybdenum β-MoC and explore the use of first principles calculation data in analysing the link between different carbides and the effects of doping elements. Supercell models with different defect types were established and optimized, and the formation energy data of defects was developed. The structure evolution during the optimization process is analysed in detail to establish the main characteristics of changes and the relevant electronic properties. The data for different types of intrinsic defects and combined defects complexes was developed and key results is analysed. The results show that carbon vacancy (V) is stable but does not inevitably exist in pure β-MoC. Interstitial site II is a very unstable position for any type of atoms (Mo, V and C), and analysis of the structure evolution shows that the atom always moves to the interface area near the interstitial site I between two layers. In particular, a C atom can expand the lattice structure when it exists between the layer interfaces. One type of the defects studied, the substitution of Mo with V (designated as 'S'), is the most stable defect among all single point defects. The data for defect complexes shows that the combination of multiple S defects in the super cell being more stable than the combination of other defects (e.g., 'V+I', 'S+V'). The data with increasing S in (Mo, V)C system is developed, and typical data (e.g., formation energy) for Mo-rich carbides and V carbides are correlated and the potential of the data in analysing transition of different carbides is highlighted. The relevance of using first principles calculation data in the studying of V-doping and the complex carbides (V- and Mo-rich carbides) evolution in different materials systems and future focus of continuous work is also discussed.
在本文中，采用第一性原理方法研究了钼β-MoC中的点缺陷、钒相关缺陷以及缺陷组合（空位（V）、替代（S）和/或间隙（I）），并探索了利用第一性原理计算数据来分析不同碳化物之间的联系以及掺杂元素的影响。建立并优化了具有不同缺陷类型的超晶胞模型，得出了缺陷的形成能数据。详细分析了优化过程中的结构演变，以确定变化的主要特征和相关的电子性质。得出了不同类型本征缺陷和复合缺陷复合体的数据，并对关键结果进行了分析。结果表明，碳空位（V）是稳定的，但在纯β-MoC中并非必然存在。间隙位置II对于任何类型的原子（Mo、V和C）来说都是非常不稳定的位置，结构演变分析表明，原子总是移动到两层之间间隙位置I附近的界面区域。特别是，一个C原子存在于层界面之间时可以扩展晶格结构。所研究的一种缺陷，即用V替代Mo（记为“S”），是所有单点缺陷中最稳定的缺陷。缺陷复合体的数据表明，超晶胞中多个S缺陷的组合比其他缺陷（如“V+I”、“S+V”）的组合更稳定。得出了（Mo，V）C体系中S含量增加的数据，并将富Mo碳化物和V碳化物的典型数据（如形成能）进行了关联，突出了这些数据在分析不同碳化物转变方面的潜力。还讨论了在不同材料体系中利用第一性原理计算数据研究V掺杂和复合碳化物（富V和富Mo碳化物）演变的相关性以及后续持续工作的重点。
