Low-temperature Maxwell-Wagner relaxation in (Na + Nb) co-doped rutile TiO2 colossal permittivity ceramics

The exact mechanism of the stunning colossal permittivity behavior found in (donor-acceptor) co-doped TiO₂ system still remains enigmatic. This behavior results from a thermally activated dielectric relaxation occurring below 50 K. Herein, thermally stimulated depolarization current analysis combined with dielectric investigation was used to disentangle this relaxation in (Na + Nb) co-doped TiO₂ ceramics. We find that this relaxation is related to frozen electrons and features the Vogel-Fulcher behavior and negative dielectric tunability. Our results reveal that this low-temperature relaxation is a new kind of Maxwell-Wagner relaxation. Differences between the low-temperature Maxwell-Wagner relaxation and its high-temperature counterpart are discussed. This study provides new insights into the physics of the eye-catching dielectric properties in co-doped TiO₂ system.