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

Abstract

Non-stoichiometric Mg²⁺-Si⁴⁺ co-doping in lattice site can effectively reduce the presence of residual phases at grain boundaries and enhance the optical quality of Tb₃Al₅O₁₂(TAG) garnet transparent ceramics, outperforming traditional weight ratio single-component sintering aids. However, further experimental validation and a deeper analysis of the underlying mechanisms are required to fully understand this phenomenon. In this study, a systematic investigation was carried out to explore the effects of non-stoichiometric Mg²⁺-Si⁴⁺ co-doping on the sintering process of TAG ceramics. Through extensive experiments and analyses, the solid-solution behavior of Mg²⁺/Si⁴⁺ at various sintering stages was revealed, and its correlation with densification, phase evolution, and microstructure of the grain boundary was disclosed. Through analysis of lattice parameter and oxygen vacancy concentration change, it was found that Si⁴⁺ enters the lattice earlier than Mg²⁺, and as temperature increases, the presence of Si⁴⁺ in turn enhances the solid solubility of Mg²⁺. By precisely controlling the Mg²⁺/Si⁴⁺ atomic 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.