Sintering and grain growth in SiO2 doped Nd:YAG

Densification and grain growth in pure YAG, SiO2 doped YAG and SiO2 doped Nd:YAG were explored. The activation energy for densification (235 kJ/mol) in pure YAG is lower than that of grain growth (946 kJ/mol) which is unusual in ceramic systems. Consequently, pure YAG sinters to near full density (>99.9%) at 1700 °C with little grain growth (1.2 μm average grain size). The remaining large pores (radius > 2 μm) were determined to be thermodynamically stable because their coordination number with grains was >6. The stability of these pores underscores the importance of powder processing and forming in fabricating transparent YAG. SiO2 doped YAG sinters to near full density 100 °C lower than pure YAG because SiO2 enables liquid phase sintering and the removal of large pores. The addition of Nd2O3 further enhances both densification and grain growth at temperatures below 1700 °C. Above 1700 °C higher concentrations of Nd3+ suppressed grain growth, possibly due to solute drag.