Investigations on the liquid phase in barium titanate ceramics with silica additives

Additives of SiO2 lower the sintering temperature of BaTiO3 ceramics and promote anomalous grain growth. However, the nature of the working liquid phase is not clear. A binary eutectic is out of the question because the system BaTiO3–SiO2 is not a binary one, as shown by Robbins [Robbins, C. R., Synthesis and growth of fresnoite (Ba2TiSi2O8) from a TiO2 flux and its relation to the system BaTiO3–SiO2. Journal of Research of the National Buereau of Standards — A. Physics and Chemistry, 1970, 74A, 229–232]. Guha and Kolar [Guha, J. P. and Kolar, D., Phase equilibria, sintering characteristics and dielectric properties in the BaTiO3-rich portion of the system BaO–TiO2–SiO2. In 5th Conference on Ceramics for Electronics, Liblice, 1974, pp. 1–9] found a ternary eutectic with a composition of 33 mol% BaO, 54 mol% TiO2 and 13 mol% SiO2. We examined powder tips of this composition and ones of pure SiO2 in contact with BaTiO3 green bodies by heating microscopy. The results suggest that the ternary eutectic develops in sintering bodies with SiO2 addition. During further sintering the composition of the liquid phase is changed and this modified melt is able to trigger anomalous grain growth.