Mechanism of the liquid-phase sintering for Nd:YAG ceramics

The mechanisms of the solid-state sintering of pure Nd:YAG and of the liquid-phase sintering of silica-doped Nd:YAG ceramics have been studied during the present work.On one hand, the densification mechanism of undoped Nd:YAG ceramics which obeys to a solid-state sintering has been investigated. It appeared from the kinetical tests performed under isothermal conditions (between 1723 and 1823 K) that densification is a thermally activated process during the intermediate stage of solid-state sintering. The activation energy so-determined (600 kJ mol−1) was attributed to densification controlled by the grain boundary diffusion of rare-earth elements.On the other hand, the kinetical analysis of the liquid-phase sintering of silica-doped Nd:YAG materials has been carried out for temperature ranging between 1723 and 1823 K, i.e., for any temperature higher than the melting point (1660 K) of the silica-rich secondary phase which adopts the eutectic composition in SiO2–Al2O3–Y2O3 system. Densification rate increases versus increasing liquid content and sintering temperature. The activation energies ranged from 1145 to 986 kJ mol−1 over the relative density range of 70% to 90%, respectively. The high activation energies have been correlated to the solution-precipitation stage of sintering for which the interface reaction would be the rate-controlling step.