Effect of SiO₂ on densification and microstructure development in Nd:YAG transparent ceramics

This paper examines the influence of SiO₂ doping on densification and microstructure evolution in Nd_3xY _3-3xAl₅O₁₂ (Nd:YAG) ceramics. Nd:YAG powders were doped with 0.035-0.28 wt% SiO₂ and vacuum sintered between 1484° and 1750°C. ²⁹Si magic-angle spinning nuclear magnetic resonance showed that Si⁴⁺ substitutes onto tetrahedrally coordinated Al³⁺ sites. High-resolution transmission electron microscopy showed no grain boundary second phases for all silica levels in samples sintered at 1600°-1750°C. Coarsening was limited by a solute drag mechanism as suggested by cubic grain growth kinetics and transmission electron microscopy energy-dispersive X-ray spectroscopy observations of increased Nd³⁺ concentration near grain boundaries. Increasing SiO₂ content increased both densification and grain growth rate and led to increasingly coarsening-dominated sintering trajectories. Fine-grained (<3 μm), highly transparent (>82% real in-line transmission) ceramics were produced by sintering 0.035 wt% SiO₂-doped ceramics at 1750°C for 8 h. Coarse-grained (18 μm), transparent samples were obtained with 0.28 wt% SiO₂-doped Nd:YAG when sintered at 1600°C for 8 h.