Microstructural evolution by in-situ TEM observations of oxides

Abstract

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 BaTiO 3 due to heating, we clarify the vanishing mechanism of internal pores and the mechanism of BaCO 3 phase generation/vanishing at high temperatures. Through observations of the grain growth of BaTiO 3 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 Ba 5 Nb 4 O 15 , 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 BaLn 2 Mn 2 O 7 (Ln = Gd, Pr, Eu) reveal a first-order phase transition that has not been previously reported.

Thermally Induced Pore Formation in Epitaxial ZnO Films Grown from Low Temperature Aqueous Solution

“…The presence of lattice hydroxide has been correlated to the formation of pores in other oxides synthesized from aqueous solution, most notably in BaTiO 3 powders produced hydrothermally, where intragranular pores have been observed after heating above 400 °C. − Hennings et al have proposed that these pores form as a result of the dehydration of the BaTiO 3 powder . They propose that a large amount of hydroxide ions are incorporated into the powders during synthesis through substitution on the oxygen site.…”

Unveiling the Microscopic Origins of Phase Transformations: An in Situ TEM Perspective

“…Several in situ studies have shown clear diffusive, first-order characteristics. For example, Nakano et al 32 collected phasecontrast images and SAED patterns while heating in the TEM, revealing a previously unreported first-order phase transition in BaLn 2 Mn 2 O 7 (Ln = Gd, Pr, Eu). Nucleation and growth kinetics show that the transformation speed is temperature- dependent, characteristic of a diffusive first order transformation.…”

Effect of milling on the anisotropic grain growth in a sintered Ba5Nb4O15 specimen and its effect on microwave dielectric properties

“…21 The basal planes in the specimens prepared using the powder milled in water ( Figure 9) are observable, confirming that the basal plane is the low-energy plane. 22 These planes tend to form because of the available nuclei.…”