The charge compensation mechanism and dielectric properties of the (Al x Cr0.05-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 ε'∼ 103, which was described by self-charge compensation between Cr3+-Ta5+, suppressing the formation of Ti3+. Interestingly, ε' can be significantly increased (6.68 × 104) by re-balancing the charge compensation via triple doping with Al3+ in the Al3+/Cr3+ ratio of 1.0, while a low loss tangent (∼0.07) was obtained. The insulating grains of [Cr0.05 3+Ta0.05 5+]Ti0.9 4+O12 has become the semiconducting grains for the triple-doped Al x 3+[Cr0.05-x 3+Ta0.05-x 5+][Ta x 5+Ti x 3+Ti0.9+x 4+]O12+3x/2. Considering an insulating grain with low ε' 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 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 Al3+/Cr3+/Ta5+-doped TiO2 system for further designing the dielectric and electrical properties of TiO2-based ceramics for capacitor applications.
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