Achieving near-theoretical transmittance in MgAl2O4 ceramic at reduced sintering temperature via solution substitution

Submicron-sized powders are ideal for large-scale industrial production of MgAl₂O₄ transparent ceramics, yet their low sintering activity limits the fabrication of high-quality products. Herein, we demonstrate that the sinterability of MgAl₂O₄ can be significantly improved through appropriate cation substitution. Specifically, by substituting 25 mol% Ga³⁺ for Al³⁺, the temperature required for completing pore closure by pressureless sintering was reduced by 125 °C (1450 °C) and the temperature for achieving near-theoretical transmittance via hot isostatic pressing post-treatment lowered by 300 °C (1500 °C). Such a marked effect may be attributed to the weakened octahedral bonding strength, which accelerates the formation and diffusion of oxygen vacancies upon sintering. Although excessive Ga³⁺ degrades intrinsic hardness, the MgAl_1.5Ga_0.5O₄ ceramic obtained still reached a high hardness (∼13.62 GPa) due to its fine-grained microstructure, compared to the no Ga-addition counterpart. This study provides insights into the rational design of solid solutions with high sintering activity.