Dielectric properties of B-doped CaCu₃Ti₄O ₁₂ ceramics

CaCu₃Ti₄O₁₂ (CCTO) exhibiting high dielectric constants has recently attracted considerable attention because of the high dielectric constant of about 10⁵ at radio frequency and good temperature stability over a wide temperature range. But high dielectric loss and low breakdown strength seriously affect its application. B₂O ₃ is chosen as glassy phase and it can make grain grow rapidly and decrease the sintering temperature. Meanwhile, B₂O₃ can improve the breakdown strength of CCTO and decrease dielectric loss due to the increase of the density. It can be observed that B₂O₃ precipitate in grain boundaries and increase the resistance of grain boundary. The main CaCu₃Ti₄O₁₂ phase was confirmed by X-ray diffraction, the microstructure with obvious grain and grain boundary structures was observed by scanning electron microscopy. This study indicates that the amount of B₂O₃ can increase the dielectric constant of CCTO keeping 10⁴ in the frequency range from 10 ^-1 Hz to 10⁶ Hz and can also decrease the dielectric loss of CCTO since it can increase the resistance of the grain boundary. For the sample doped with 3 wt % B₂O₃, its dielectric constant is stable from 10^-1 Hz to 10⁶ Hz, the tanδ decrease to 0.06 compared with 0.7 at 1 kHz of the undoped CCTO sample, and its grain boundary resistance is obvious much bigger than other samples.