Synergistic improvement of flexural strength and fracture toughness in Si₃N₄ ceramics featuring high-entropy grain boundary phase

Developing silicon nitride (Si₃N₄) ceramics with concurrently enhanced flexural strength and fracture toughness presents significant challenges due to the critical dependence of these macroscopic properties on microstructure. This study produced high-performance Si₃N₄ ceramics by employing multiple rare earth (RE) oxides (RE₂O₃) as sintering additives to construct a multicomponent rare earth ion liquid phase via hot pressing sintering (HPS). The designed multicomponent RE-ion liquid phase reduces the shrinkage onset temperature while facilitating densification and α→β phase transformation. Synergistic effects among the multicomponent RE-ion liquid phase foster a distinct bimodal microstructure characterized by an optimized spatial distribution of refined matrix grains interlocked with elongated rod-like β-Si₃N₄ grains exhibiting elevated aspect ratios. Concurrently, the multicomponent RE-ion liquid phase crystallizes into a high-entropy (Gd_0.2Y_0.2Yb_0.2Lu_0.2Sc_0.2)₂Si₂O₇, enabling high crystallinity of the grain boundary phase in Si₃N₄ ceramics. Through concurrent optimization of microstructure and grain boundary phase properties in Si₃N₄ ceramics, synergistic enhancement in flexural strength (1322 MPa) and fracture toughness (10.88 MPa·m^1/2) is achieved. Collectively, this high-entropy approach establishes a highly promising transformative strategy for developing high-performance structural ceramics.