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-control ling step. (C) 2008 Elsevier B.V. All rights reserved.