Roles of non-stoichiometric Mg2+-Si4+ co-doping in the sintering process of TAG ceramics with higher optical quality

Compared with sintering aids added in a single traditional weight ratio, non-stoichiometric Mg2+-Si4+ co-doping in lattice site has been found to significantly enhance the optical quality of garnet transparent ceramics for solid-state laser systems by reducing grain boundary residues. However, its specific roles and mechanisms at different stages of ceramic sintering remain unclear. In this work, we systematically investigated the effects of non-stoichiometric Mg2+-Si4+ co-doping on the sintering process of TAG ceramics, revealing the solid-solution behavior of Mg/Si at different stages and its relationship with densification, phase evolution, and microstructure of grain boundary. Through analysis of lattice parameter and Oxygen vacancy concentration change, it was found that Si enters the lattice earlier than Mg, and as temperature increases, the presence of Si in turn enhances the solid solubility of Mg. By precisely controlling the Mg/Si doping ratio, optimized control of the densification process was achieved. TEM analysis of the optimal sample's grain boundaries showed that under high addition amounts of MgO and TEOS, the non-stoichiometric design method significantly reduced grain boundary residual phases. This discovery highlights the importance of synergistic optimisation of aids species and content under non-stoichiometric doping for preparing higher optical quality garnet transparent ceramics.