Improved microstructure and significantly enhanced dielectric properties of Al3+/Cr3+/Ta5+ triple-doped TiO2 ceramics by Re-balancing charge compensation

The charge compensation mechanism and dielectric properties of the (AlxCr0.05-x)Ta0.05Ti0.9O2 ceramics were studied. The mean grain size slightly changed with the increase in the Al3+/Cr3+ ratio, while the porosity was significantly reduced. The dielectric permittivity of the co-doped Cr0.05Ta0.05Ti0.9O2 ceramic was as low as epsilon 'similar to 10(3), which was described by self-charge compensation between Cr3+-Ta5+, suppressing the formation of Ti3+. Interestingly, epsilon ' can be significantly increased (6.68 x 10(4)) by re-balancing the charge compensation via triple doping with Al3+ in the Al3+/Cr3+ ratio of 1.0, while a low loss tangent (similar to 0.07) was obtained. The insulating grains of [Cr0.053+Ta0.055+]Ti0.94+O12 has become the semiconducting grains for the triple-doped Al-x(3+)[Cr0.05-x3+Ta0.05-x5+][Tax5+Tix3+Ti0.9+x4+]O12+3x/2. Considering an insulating grain with low epsilon ' of the Cr0.05Ta0.05Ti0.9O2 ceramic, the electron-pinned defect-dipoles and interfacial polarization were unlikely to exist supported by the first principles calculations. The significantly enhanced epsilon ' value of the triple-doped ceramic was primarily contributed by the interfacial polarization at the interface between the semiconducting and insulating parts, which was supported by impedance spectroscopy. This research gives an underlying mechanism on the charge compensation in the Al3+/Cr3+/Ta5+-doped TiO2 system for further designing the dielectric and electrical properties of TiO2-based ceramics for capacitor applications.

Automated summary

The research shows that the charge compensation mechanism and doping ratio play a significant role in controlling the dielectric properties of (AlxCr0.05-x)Ta0.05Ti0.9O2 ceramics. Triple doping with Al3+ can greatly increase the dielectric permittivity by rebalancing the charge compensation, while maintaining a low loss tangent. The enhanced dielectric properties of the ceramics are primarily attributed to the interfacial polarization at the interface between semiconductor and insulating grains.