New design concept for stable alpha-silicon nitride based on the initial oxidation evolution at the atomic and molecular levels

CY Guo and EH Wang and Z Fang and YP Zheng and T Yang and ZJ He and XM Hou, JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 122, 156-164 (2022).

DOI: 10.1016/j.jmst.2022.01.016

As the dominated composition of Si3N4 ceramics, a-silicon nitride (alpha-Si3N4) can satisfy the strength and fracture toughness demand in the applications. However, alpha-Si3N4 is oxygen-sensitive at high temperatures, which limits its high-temperature performance. To improve the oxidation resistance of alpha-Si3N4 ceramics, it is necessary to shed light on the oxidation mechanism. Herein, the initial oxidation of alpha-Si3N4 was systematically studied at the atomic and molecular levels. The density functional theory (DFT) calculation denotes that the (001) surface of alpha-Si3N4 has the best stability at both room temperature and high temperature. Besides, the oxidation process of the alpha-Si3N4 (001) surface consists of O adsorption and N desorption, and the consequent formation of nitrogen-vacancy (V-N) is the key step for further oxidation. Moreover, the molecular dynamics (MD) simulation indicates that the oxidation rate of alpha-Si3N4 (100) surface is slower than that of alpha-Si3N4 (001) surface due to the lower N concentration at the outermost layer. Therefore, the oxidation resistance of alpha- Si3N4 can be improved by regulating the (100) surface as the dominant exposure surface. In addition, reducing the concentration of N on the final exposed surface of alpha-Si3N4 by mean of constructing the homojunction of the Si-terminal (100) surface and other N-containing surfaces (such as (001) surface) should be also a feasible approach. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

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