Coupled roles of MgF2 additive on sintering of sub-micron alumina transparent ceramics

Abstract

High-quality transparent Al₂O₃ ceramics were successfully prepared using MgF₂ as a sintering additive. Comprehensive investigations involving microstructure characterization, optical/mechanical properties, and sintering kinetics analysis found that F anions play a dominant role in enhancing densification with slight effects on grain size. While Mg cations primarily suppress grain growth through solute drag effects. Significantly, the combining functions of Mg and F confer MgF₂ remarkable superiority over both conventional spinel and AlF₃ additives upon the preparation of transparent Al₂O₃ ceramics. Consequently, MgF₂-doped Al₂O₃ ceramics with the optimum dopant content (500 ppm) present the highest in-line transmittance of 61.6 % at 640 nm alongside superior mechanical properties (hardness of 21.8 GPa, indentation fracture toughness of 2.73 MPa·m^1/2). By elucidating the coupled sintering roles of Mg-F pair, this work provides a novel paradigm for designing dual-functional additives in transparent Al₂O₃ ceramics.