Results and Discussion High-performance Si₃N₄ ceramics were successfully produced through hot-press sintering. As the mass fraction of metallic Yb increased, the density of Si₃N₄ ceramics showed an upward trend, while the relative density gradually decreased. The grain size of β-Si₃N₄ initially increased with higher Yb content but subsequently stabilized. After heat treatment at 1 850 ℃ for 5 hours， the thermal conductivity of Si₃N₄ ceramics was significantly improved, increasing from 36. 8 W/m·K to 66. 8 W/m·K, representing an 82% enhancement. During this process, the loaded metallic Yb was transformed into ytterbium nitride (YbN), which preferentially reacted with the inherent SiO₂ on the surface of Si₃N₄ powder. This reaction increased the nitrogen-to-oxygen ratio in the sintering liquid phase and reduced the oxygen content in the Si₃N₄ lattice. Consequently, the thermal conductivity of the Si₃N₄ ceramics was improved.

Conclusion In a liquid ammonia medium, rare-earth Yb, characterized by its high oxygen affinity, was in-situ loaded onto the surface of Si₃N₄ powder as a sintering aid. This approach effectively reduces the lattice oxygen content in Si₃N₄ ceramics and enhances their sintering properties, offering a novel strategy for the fabrication of high-thermal-conductivity Si₃N₄ ceramics.

Keywords：Si₃N₄ ceramics; rare earth loading; dissolution-precipitation; thermal conductivity