Colossal permittivity properties of Zn,Nb co-doped TiO₂ with different phase structures

Colossal permittivity properties were studied in Zn,Nb co-doped TiO₂ with different phase structures. The (Zn_1/3Nb_2/3)_0.05Ti_0.95O₂ rutile ceramics were prepared by the solid state sintering technique, while the amorphous and anatase films were respectively fabricated by a pulsed laser deposition method and a subsequent rapid thermal annealing. The ceramics showed a frequency (10²-10⁶ Hz) independent dielectric response with a colossal dielectric permittivity (∼30 000), and a relatively low dielectric loss (∼0.05) at room temperature. The excellent colossal permittivity properties are comparable to those of the previously reported rutile TiO₂ ceramics by co-doping trivalent and pentavalent elements. For amorphous films, the dielectric permittivity decreased, and the dielectric loss increased slightly compared to those of the ceramics. Compared with the amorphous thin films, the annealed anatase ones exhibited a simultaneous increase in both dielectric permittivity and loss at low frequency while kept almost unchanged at high frequency. These results suggest that co-doping of bivalent elements with Nb into TiO₂ with various phase structures can yield colossal permittivity effects, including ultra-high dielectric permittivity, relatively low dielectric loss. Furthermore, the colossal permittivity properties may be mainly attributed to the effect of the electron-pinned defect-dipoles in Zn,Nb co-doped TiO₂ with different phase structures rather than the grain boundary capacitance effect. Besides, the frequency and bias dependent dielectric properties were also investigated in thin film forms, which could be affected by the electrode-film interface and mobile ions. Our results are helpful for not only investigating the new class of colossal permittivity materials, but also developing dielectric thin film device applications.