Reaction Synthesis and Mechanical Properties of Lu4 Si2 O7 N2.

Crystallized Lu- Si- O- N phases were believed to be the grain-boundary ( GB) phases that might provide Si₃ N₄ 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 Lu₂ O₃, SiO₂, and Si₃ N₄ powder mixtures (with the stoichiometry of 4:0.96:1) from room temperature to 1600°C. Thereafter, dense Lu₄ Si₂ O₇ N₂ 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 Lu₄ Si₂ O₇ N₂ 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 Lu₄ Si₂ O₇ N₂ as a promising target GB phase for the optimization of high-temperature mechanical properties of Si₃ N₄. [ABSTRACT FROM AUTHOR]