Colossal dielectric permittivity in hydrogen-reduced rutile TiO2 crystals

(Nb + In) co-doped rutile TiO2 (TINO) ceramics have received considerable attention, due to their high dielectric permittivity (on the order of 10,000) and low loss factor (<0.05) over a broad temperature/frequency range. The high dielectric permittivity of TINO has been attributed to a special defect-dipole structure. Here, we observed a similar dielectric behavior in hydrogen-reduced rutile TiO2 crystals, where the colossal dielectric permittivity of ∼30,000 and the low loss factor of ∼0.05 exist in the temperature range of 30-480 K (frequency at 10∼105 Hz). Based on the investigations on the phase microstructures, the elemental valences, impedance spectroscopy, nonlinear I-V behavior and dielectric response, the colossal dielectric permittivity of the hydrogen-reduced rutile TiO2 crystals was thought to be associated with the electronic relaxation polarization mechanism. This research further revealed that the weak-binding electron is the most critical factor for the high dielectric permittivity in rutile TiO2 system, while a special defect-dipole structure may not be a preliminary requirement.