The Nd3+ cation diffusion into transparent polycrystalline YAG was investigated as a function of temperature and silica content. Thin neodymium oxide layers were deposited on sintered YAG substrates prior to annealing under air at 1400 to 1600C. Bulk and grain boundary neodymium diffusion coefficients were measured by secondary ion mass spectrometry. The experimental results showed that silica addition increases the diffusivity of Nd3+ by a factor 10 whatever the diffusion path, probably as a result of extrinsic point defects formation, especially rare-earth vacancies. The experimental diffusion data were used to elucidate the sintering mechanism of Nd:YAG ceramics at 1450 to 1550C. Firstly, it appeared that the intermediate stage of solid-state sintering should be controlled by the rare-earth diffusion along the grain boundary with an activation energy of about 600kJ/mol. Secondly, grain growth mechanism at the final stage of liquid-phase sintering was investigated for silica-doped Nd:YAG samples. Thus, the grain growth should be limited by the reaction at interfaces at below 1500C, with an activation energy of about 880kJ/mol. At higher temperature, it seems to be limited by the ionic diffusion through the intergranular liquid phase, with an activation energy of 250kJ/mol.

The Effect of Silica Doping on Neodymium Diffusion in Yttrium Aluminum Garnet Ceramics: Implications for Sintering Mechanisms. R.Boulesteix, A.Maître, J.F.Baumard, Y.Rabinovitch, C.Sallé, S.Weber, M.Kilo: Journal of the European Ceramic Society, 2009, 29[12], 2517-26