Colossal Permittivity and Ferroelectricity in TiO2-Based Ceramics Induced by Defect Clusters

The substitution of donor-acceptor ion pairs in metal oxides creates local chemically unstable states, thereby altering properties and even generating functions unattainable in the host materials. Herein, ferroelectricity and colossal permittivity responses are co-evoked in rutile TiO2 ceramics via the donor-acceptor (Nb5+-Mg2+) ionic pairs co-doping strategy. The large ionic radii of the acceptor Mg2+ ions and donor Nb5+ ions replacing Ti4+ ions disrupt the local chemical stability states and induce lattice strain. Defect clusters formed by localized chemical valence imbalance undergo polarization, generating a local built-in electric field. This electric field drives the long-range ordered arrangement of defect clusters, endowing the co-doped TiO2 ceramics with room-temperature ferroelectricity. Furthermore, defect clusters and the local electric field also restrict the long-range migration of charge carriers, enabling the Nb5+-Mg2+ pairs co-doped TiO2 ceramics to achieve a high dielectric constant (ε' = 40,000) while maintaining an acceptably low loss (tan δ = 0.063). This work proposes an approach for designing centrosymmetric oxides with combined ferroelectric and giant dielectric properties, offering excellent application prospects for multifunctional microelectronic components.