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

作者：Guo, Chunyu; Wang, Enhui^*; Fang, Zhi; Zheng, Yapeng; Yang, Tao; He, Zhijun; Hou, Xinmei^*

来源：JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 2022, 122: 156-164.

DOI：10.1016/j.jmst.2022.01.016

• alpha-Si3N4
• Surface oxidation
• Nitrogen vacancy
• DFT
• MD

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.

• 单位
  北京科技大学