Insight into Point Defects and Complex Defects in β-Mo2C and Carbide Evolution from First Principles

Jing Guo; Yunli Feng; Cong Tang; Li Wang; Xiaoliang Qing; Qingxiang Yang; Xuejun Ren

doi:10.3390/ma15134719

Insight into Point Defects and Complex Defects in β-Mo₂C and Carbide Evolution from First Principles

Materials (Basel). 2022 Jul 5;15(13):4719. doi: 10.3390/ma15134719.

Authors

Jing Guo^{1

2}, Yunli Feng², Cong Tang¹, Li Wang³, Xiaoliang Qing¹, Qingxiang Yang⁴, Xuejun Ren¹

Affiliations

¹ School of Engineering, Faculty of Engineering and Technology, Liverpool John Moores University, Liverpool L3 3AF, UK.
² Hebei Key Laboratory of Modern Metallurgy Technology, College of Metallurgy and Energy, North China University of Science and Technology, Tangshan 063009, China.
³ School of Engineering and Materials, Queen Mary University of London, London E1 4NS, UK.
⁴ State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.

Abstract

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-Mo₂C 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_C) is stable but does not inevitably exist in pure β-Mo₂C. 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_V-Mo'), is the most stable defect among all single point defects. The data for defect complexes shows that the combination of multiple S_V-Mo defects in the super cell being more stable than the combination of other defects (e.g., 'V_Mo+I_C', 'S_V-Mo+V_C'). The data with increasing S_V-Mo in (Mo, V)₂C 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.

Keywords: defect combination; first-principles calculation; formation energy; phase engineering; phase transition; point defect; β-molybdenum carbides (Mo2C).

Grants and funding

793114, 823786/European Union