High Resolution Transmission Electron Microscopy Observations on Sintering Processes in KNbO3 Ceramics
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A homogeneous KNbO3 (KN) phase was formed by sintering at 1,040oC for 1 hour, without formation of the K2O-deficient secondary phase even though suffering the minor loss of K2O. KN liquid phase was formed during sintering and abnormal grain growth occurred in this specimen. The detailed microstructural observations on KN during sintering were carried out using high resolution transmission electron microscopy. The ledged structures were found at the KN grain boundary and the abnormal grain growth was performed by the lateral migration of these ledges in the presence of the liquid phase. The liquid pockets were found in the KN grains. They have various external shapes mainly due to the kinetic factors. They have atomically flat interfaces with some ledges with one atomic height. The slight deficient K2O by evaporation might somewhat reduce the melting point of KN from the reported at 1,058oC. The liquid pockets play an important role in supplying the liquid phase during the abnormal grain growth in the sintering process of KN ceramics.
Abstract
A homogeneous KNbO3 (KN) phase was formed by sintering at 1,040oC for 1 hour, without formation of the K2O-deficient secondary phase even though suffering the minor loss of K2O. KN liquid phase was formed during sintering and abnormal grain growth occurred in this specimen. The detailed microstructural observations on KN during sintering were carried out using high resolution transmission electron microscopy. The ledged structures were found at the KN grain boundary and the abnormal grain growth was performed by the lateral migration of these ledges in the presence of the liquid phase. The liquid pockets were found in the KN grains. They have various external shapes mainly due to the kinetic factors. They have atomically flat interfaces with some ledges with one atomic height. The slight deficient K2O by evaporation might somewhat reduce the melting point of KN from the reported at 1,058oC. The liquid pockets play an important role in supplying the liquid phase during the abnormal grain growth in the sintering process of KN ceramics.
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