Reaction Synthesis and Mechanical Properties of Lu4Si2O7N2

Crystallized Lu–Si–O–N phases were believed to be the grain‐boundary (GB) phases that might provide Si₃N₄ with excellent high‐temperature mechanical properties. However, little is known about the intrinsic properties, as well as the synthesis, of the Lu–Si–O–N ceramics. This work reveals the reaction paths of heating Lu₂O₃, SiO₂, and Si₃N₄ powder mixtures (with the stoichiometry of 4:0.96:1) from room temperature to 1600°C. Thereafter, dense Lu₄Si₂O₇N₂ samples are synthesized by in situ reaction/hot‐pressing method, and the mechanical properties at room temperature and elevated temperatures are reported for the first time. The Lu₄Si₂O₇N₂ samples show significant high‐temperature mechanical properties, such as the elastic stiffness remains 77% from room temperature to 1500°C; and bending strength keeps 93% from room temperature to 1400°C. The present results shine a light on Lu₄Si₂O₇N₂ as a promising target GB phase for the optimization of high‐temperature mechanical properties of Si₃N₄.