Effect of Microstructure on the Reliability of BaTiO3 under DC Electric Field
Date Issued
2010
Date
2010
Author(s)
Chen, Yin-Hua
Abstract
Barium titanate-based ceramics are used extensively because of their superior ferroelectric properties. The microstructure characteristics of BaTiO3 play important roles on the ferroelectric performance. In the present study, BaTiO3 specimens with different microstructure are prepared by using various sintering profiles. A discontinuous grain growth, also called abnormal grain growth (AGG) or exaggerated grain growth (EGG), is observed in some specimens. The microstructure of the specimens sintered at 1320-1360℃ exhibits a typical bimodal structure. Through the quantitative characterization, the size variation of normal and abnormal grains is determined. The average size of normal grains varies from 1.9 to 2.2 μm and abnormal grains from 122 to 211 μm. The size difference between the normal and abnormal grains is two orders of magnitude. No grain with an intermediate size is observed. A “pseudo-abnormal” region with a cluster of fine grains is found during the microstructure observation. The formation of pseudo-abnormal regions may provide a microstructure transition from normal to abnormal grains.
The reliability of barium titanate under DC electric field is also investigated in the present study. The highly accelerated life test (HALT) method is used to estimate the reliability for long-term usage. The distribution of lifetime is analyzed by using the Weibull statistics. The Weibull modulus of the BaTiO3 ceramics is in the range of 0.21-0.52. The DC breakdown voltage test is also applied to obtain the dielectric strength (DS) of the BATiO3 specimens. The dielectric strength is in the range of 5.7- 11 MV/m. When the area fraction of abnormal grains is higher, the dielectric strength is smaller. Through the microstructure observation on the fracture surface, the mechanism of the dielectric breakdown is different from that of specimens under the breakdown tests. For the DC breakdown voltage test, the growth of microcracks caused by the electrically induced effect is the reason for the breakdown. And for the HALT, it is thought to be dominated by thermal runaway (TRA) which is caused by the localized heating.
Subjects
Barium titanate
Microstructure
Abnormal grain growth
Highly accelerated life time (HALT)
Dielectric breakdown
Reliability
Dielectric strength
Thermal runaway
Type
thesis
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