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Structures of WxNy Crystals and Their Intrinsic Properties: First-Principles Calculations

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journal contribution
posted on 01.03.2018 by Zhixiong Kang, H. Y. He, Rui Ding, Junling Chen, B. C. Pan
Recent experiments had shown that nitrogen (N) may react with the tungsten (W) atoms at the surface of W-based plasma facing materials (PFM) in a fusion reactor to form WN compounds. The formed WN compounds exhibit excellent performance in retention of deuterium, which is essentially correlated with the atomic structures of the WN compounds. Unfortunately, the structural features of WxNy crystals with different stoichiometric ratios are not systematically made clear. In this paper, we report our systematic study on WxNy structures (x = 1–6, y = 1–6) based on density functional theory (DFT) combined with a particle-swarm optimization (PSO) technique. The lowest-energy WxNy structures (x = 1–6, y = 1–6) are proposed. It is found that the concerned WN compounds characterize metallic feature, except for W1N2 which is a semiconductor. Meanwhile, the evolution of the mechanical properties of the compounds on the N-to-W ratio for WxNy structures is investigated. It reveals that the good mechanical properties of a compound is associated with the presence of covalence bonds besides the common existence of ionic and/or metallic bonds in the compound.