Abstract
During sintering in an air atmosphere, barium titanate ceramics frequently exhibit exaggerated grain growth. Discontinuous grain growth is particularly rapid in the presence of the Ti-rich eutectic and results in coarse, equiaxed grains with broad size distribution. During sintering under reducing conditions, above the BaTiO3-Ba6Ti17O40 eutectic temperature, barium titanate ceramics exhibit characteristically exaggerated anisotropically grown grains, which were identified as the hexagonal polymorph, known to be formed above 1460°C in air, and at ~1330° C in hydrogen. The hexagonal grains are platelets with high aspect ratio.
Change in morphology strongly depends on sintering temperature, impurity/dopants concentration, and amount of liquid phase. Kinetics studies confirmed that the liquid eutectic promotes the cubic-hexagonal transformations. The growth mechanism of hexagonal grains is dissolution of small cubic grains and precipitation on the hexagonal grains which preferentially grow in the direction of the prism planes. The initially high aspect ratio >50 decreases after grain impingement. Increase of the amount of liquid phase and increase of temperature increase the number of nucleation sites which results in smaller grain size after short sintering time.
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Kolar, D., Rečnik, A., Čeh, M. (1998). The Origin and Growth Kinetics of Plate-Like Abnormal Grains in Liquid Phase Sintered Barium Titanate. In: Tomsia, A.P., Glaeser, A.M. (eds) Ceramic Microstructures. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-5393-9_30
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DOI: https://doi.org/10.1007/978-1-4615-5393-9_30
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