Improved microstructure and significantly enhanced dielectric properties of Al 3+ /Cr 3+ /Ta 5+ triple-doped TiO 2 ceramics by Re-balancing charge compensation.

The charge compensation mechanism and dielectric properties of the (Al x Cr 0.05- x )Ta 0.05 Ti 0.9 O 2 ceramics were studied. The mean grain size slightly changed with the increase in the Al 3+ /Cr 3+ ratio, while the porosity was significantly reduced. The dielectric permittivity of the co-doped Cr 0.05 Ta 0.05 Ti 0.9 O 2 ceramic was as low as ε '∼ 10 3 , which was described by self-charge compensation between Cr 3+ -Ta 5+ , suppressing the formation of Ti 3+ . Interestingly, ε ' can be significantly increased (6.68 × 10 4 ) by re-balancing the charge compensation via triple doping with Al 3+ in the Al 3+ /Cr 3+ ratio of 1.0, while a low loss tangent (∼0.07) was obtained. The insulating grains of [Cr 0.05 3+ Ta 0.05 5+ ]Ti 0.9 4+ O 12 has become the semiconducting grains for the triple-doped Al x 3+ [Cr 0.05- x 3+ Ta 0.05- x 5+ ][Ta x 5+ Ti x 3+ Ti 0.9+ x 4+ ]O 12+3 x /2 . Considering an insulating grain with low ε ' of the Cr 0.05 Ta 0.05 Ti 0.9 O 2 ceramic, the electron-pinned defect-dipoles and interfacial polarization were unlikely to exist supported by the first principles calculations. The significantly enhanced ε ' 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 Al 3+ /Cr 3+ /Ta 5+ -doped TiO 2 system for further designing the dielectric and electrical properties of TiO 2 -based ceramics for capacitor applications.