Microstructural evolution by in-situ TEM observations of oxides

概要

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In-situ observations using high-temperature transmission electron microscopy (TEM) is a promising technique for obtaining new findings and developing phenomenological theory for ceramic materials at high temperatures. By observing the changes in hydrothermal BaTiO3 due to heating, we clarify the vanishing mechanism of internal pores and the mechanism of BaCO3 phase generation/vanishing at high temperatures. Through observations of the grain growth of BaTiO3 prepared by radio-frequency plasma chemical vapor deposition, we calculate the grain-boundary diffusion coefficient, which is an important parameter controlling the sinterability of ceramics. Observations of the shrinkage and disappearance of Ba5Nb4O15, as well as simulations, indicate that high energy and low diffusivity at the grain boundary make grains vanish while maintaining a truncated spherical shape. Finally, observations of the structural changes in layered perovskite BaLn2Mn2O7 (Ln = Gd, Pr, Eu) reveal a first-order phase transition that has not been previously reported.