Nd:YAG transparent ceramics for laser applications: Influence of green compact microstructure on its reactivity during reaction-sintering and resulting optical properties

The influence of the microstructural features (i.e. porosity content and pore size distribution) of Y2O3–Al2O3–Nd2O3 mixed powder compacts on their reactivity during reaction-sintering has been studied. By using either Uniaxial Pressing (UP) or Cold Isostatic Pressing (CIP), it was possible to control the pore size distribution and compacity of green pellets. It was put in evidence that a higher compacity and green compact homogeneity, promoted by using the CIP process, increases the reaction sequence kinetics leading to the desired Nd:YAG phase at a reduced temperature. Also, the examination of sintering maps has shown that the sintering trajectories and the whole sintering stages are affected by the initial compacity. By increasing the initial compacity, the formation of a small amount of intragranular porosity cannot be totally avoided, but densification is favored over grain growth. As a result, better optical properties and high laser performances were obtained.