Effects of microstructures on the dielectric and ferroelectric properties of BaTiO3
Date Issued
2006
Date
2006
Author(s)
Lu, Shih-Chun
DOI
en-US
Abstract
Due to the unique dielectric and ferroelectric properties, barium titanate has been widely used as positive temperature coefficient thermistors, piezoelectrics, capacitors, and dynamic memory etc. In the present study, five sintering conditions are applied to produce the specimens with various microstructures. The effects of microstructures such as grain size and density on the dielectric and ferroelectric properties are then investigated.
Abnormal grain growth is formed in the Ti-excess BaTiO3 due to the formation of liquid phase at > 1330℃. By applying image analysis, the relationships between grain size distribution and sintering conditions are established. As the sintering temperature reaches 1335℃, abnormal grain growth is occurred; a bimodal microstructure of both fine grains and coarse grains is formed. As the sintering temperature is raised to 1350℃, the bimodal microstructure disappeared, a 100% coarse grains microstructure formed instead.
The dielectric constant increases with decreasing grain size and increasing density. The insulation resistivity is dependent of the density, showing a increase with increase of density. The dissipation factor is dependent of both the grain size and the density due to the domain wall movement and the absorbed water in the pores. The specimen with density＜88% shows no ferroelectric properties and a large leakage current. The coarse-grained specimen shows a higher value of remanent polarization and behaves as a soft ferroelectric material.
The fine-grained specimen shows a better resistance under cyclic electric field and exhibits a better reliability. It is due to the dielectric strength and fracture strength of fine-grained specimen is higher. We also found that silver migration is taken place when a cyclic electric field is applied. It may due to that the Ag migrate through the fatigue cracks and flaws produced by the cyclic electric field.
Subjects
鈦酸鋇
微結構
晶粒分布
介電
鐵電
絕緣電阻率
損失因子
交流電場
銀遷移
BaTiO3
microstructure
grain size distribution
dielectric
ferroelectric
insulation resistivity
dissipation factor
remanent polarization
cyclic electric field
silver migration
Type
thesis