Investigation of silicon content and distribution in YAG ceramics during the production process

Silica is typically used as a sintering aid in the production of transparent YAG (Y3Al5O12) ceramics, allowing for the achievement of nearly pore-free microstructures and the lowering of sintering temperatures. However, it was also found to introduce undesired color centers in the sintered material [1] as well as segregate at grain boundaries leading to the formation of amorphous or crystalline secondary phases (Y2SiO5) [2], which decrease the optical properties and compromise the use of the material as a laser medium. Thus, while the addition of silicon (in the form of SiO2 or as tetraethyl orthosilicate, TEOS) is often required, it is desirable to obtain materials with low Si content and homogeneous distribution. This work studies the amount of Si and its distribution in YAG and Yb:YAG ceramic materials produced by reaction sintering of a mixture of oxide powders throughout the whole preparation process. Monitoring the Si content step by step provides important information about the reproducibility and consistency of the fabrication process, crucial for any further optimization. We have shown that Laser-Induced Breakdown Spectroscopy (LIBS) allows sensitive and accurate quantification of silicon in ceramics down to 60 ppm and our experimental LIBS setup was used to analyze the evolution of the silicon content in samples at various steps of the fabrication process [3]. The distribution of Si in sintered ceramics was studied with High Resolution TEM to detect any possible nano-precipitates, and EDX nano-probe chemical analysis to check for segregation at grain boundaries and evaluate Si concentration within the YAG grains. The amount of Si present in the sintered materials has been found to be as low as 30 % of that introduced into the initial mixture. References 1. R. Gaume, Y. He, A. Markosyan and R.L. Byer, "Effect of Si-induced defects on 1 µm absorption losses in laser-grade YAG ceramics", J. Appl. Phys., 111, pp.093104, 2012 2. L. Esposito, T. Epicier, M. Serantoni, A. Piancastelli, D. Alderighi, A. Pirri, G. Toci, M. Vannini, S. Anghel and G. Boulon, "Integrated analysis of non-linear loss mechanisms in Yb:YAG ceramics for laser applications", J. Eur. Ceram. Soc., 32, pp.2273-2281, 2012 3. S.J. Pandey, M. Martinez, J. Hosta?a, L. Esposito, M. Baudelet and R. Gaume, "Quantification of SiO2 sintering additive in YAG transparent ceramics by Laser-Induced Breakdown Spectroscopy (LIBS)", Opt. Mater. Express (submitted)