Reaction Synthesis and Mechanical Properties ofLu₄Si₂O₇N₂

Abstract

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.

Low thermal conductivity of Lu4Si2O7N2: Theoretical and experimental studies

“…All these values are relatively higher than those of Y 4 Si 2 O 7 N 2 (142, 75 and 191 GPa, respectively). In addition, the Young's modulus E and shear modulus G of polycrystalline Lu 4 Si 2 O 7 N 2 sample were measured as 186 and 74 GPa, respectively, which are quite close to our theoretical values [14]. This testifies the high reliability of as-adopted calculation models and methods.…”

“…Dense and phase-pure Lu 4 Si 2 O 7 N 2 ceramics were fabricated by an in situ reaction/hot pressing method in our previous work [14]. In the present work, the temperature dependence of thermal conductivity of Lu 4 Si 2 O 7 N 2 ceramic was tested by a laser pulse method [18].…”

“…The detailed information of the preparation process as well as the as-prepared sample was described in Ref. [14]. Experimental temperature dependent thermal conductivity of asprepared Lu 4 Si 2 O 7 N 2 is measured and plotted in Fig.…”