Evolution of silicon content during the production of reactively-sintered transparent YAG ceramics

Abstract: The quantification of silicon content during the reaction sintering preparation process was studied using Laser-Induced Breakdown Spectroscopy (LIBS). YAG ceramics with different additions of silica have been analyzed at different steps of the process, and a significant drop in silica content was observed after the vacuum sintering step, which can be attributed to evaporation. 1. Introduction It is well known that silica can be used as a sintering aid in yttrium aluminum garnet (YAG) ceramics, leading to transparency. This approach has been successfully used in the 1990s with colloidal silica and TEOS and has brought many interesting results since. However, even though there are various publications dealing with the effect of silica addition on the transparency and microstructure of YAG ceramics [1-4], the number of studies on the solubility of Si in YAG and the processes occurring during the ceramics production is limited. Recently, it was shown that Laser-Induced Breakdown Spectroscopy (LIBS) can be used for the quantitative determination of the variations in stoichiometry of YAG [5] and of the amount of silica [6]. The presentation shows an analysis of the amount and distribution of silicon in YAG ceramics at different steps of the production process using reactive sintering using Laser-Induced Breakdown Spectroscopy. Monitoring the Si content step by step provides important information about the reproducibility and consistency of the fabrication process, crucial for any further optimization. 2. Experimental A set of mixtures with different silicon content was prepared from oxide powders and TEOS or SiO2. The powders were mixed, granulated, pressed, treated in air, sintered under high vacuum and annealed in air. The silicon content was characterized by Laser-Induced Breakdown Spectroscopy (LIBS) at different steps of the preparation process, collecting data from multiple shots for each measurement (see Fig. 1). For selected samples, in-depth concentration maps were obtained. 3. Results After a calibration using stoichiometric mixtures of oxides, quantitative data for samples with the addition of TEOS ranging from 0 to 1 wt% were obtained. The obtained quantification limit was 0.0463 wt.% of SiO2 (216 ppm of Si). The most important change throughout the preparation process was observed with the vacuum sintering step, where a large part of silica left the material. A variation in the silicon content inside the samples was observed, with lower concentrations at the outer parts. 4. Conclusions The analysis of silicon content in YAG ceramics with different initial additions of silica provided a clear indication of a significant drop in silicon content after the vacuum sintering step, which can be attributed to evaporation. The presented results show that LIBS offers a user-friendly solution to a better understanding of the role and behavior of sintering additives in the processing of advanced ceramics. 5. References [1] Boulesteix R., Maître A., Baumard J.-F., Sallé C., Rabinovitch Y. Opt. Mater. 31 (2009) 711-715. [2] Stevenson A. J., Li X., Martinez M. A., Anderson J. A., Suchy D. L., Kupp E. R., Dickey E. C., Mueller K. T., Messing G. L., ,,Effect of SiO2 on densification and microstructure development in Nd:YAG Transparent Ceramics," J. Am. Ceram. Soc. 94 (2011) 1380-1387. [3] J. Hosta?a, L. Esposito, A. Piancastelli, "Influence of Yb and Si content on the sintering and phase changes of Yb:YAG laser ceramics," J. Eur. Ceram. Soc 32(11), 2949-2956 (2012). [4] R. Gaume., Y. He , A. Markosyan, R. L. Byer, "Effect of Si-induced defects on 1 µm absorption losses in laser-grade YAG ceramics," J. Appl. Phys. 111(9), 093104 1-5 (2012). [5] S. J. Pandey, M. Martinez, F. Pelascini, V. Motto-Ros, M. Baudelet, R. M. Gau