Colossal permittivity and ferroelectric properties regulation of different kinds of doped TiO₂

TiO₂, a typical incipient ferroelectric material, has been extensively studied for its ferroelectric or dielectric properties, which can be achieved via donor and acceptor co-doping. However, the influence of doping ions on the performance of TiO₂ remains unclear. In this study, the relationship between the properties of TiO₂ and doping ions was investigated by selecting acceptors with various ionic radii. Colossal permittivity in TiO₂ was achieved by doping large-ionic-radius acceptors, forming defect complexes to pin electrons and mitigate dielectric loss. For small acceptor ionic radii, donor–acceptor co-doped TiO₂ exhibited ferroelectricity at room temperature. The electric dipole moment formed by the donor and acceptor readily rotated under an external electric field, resulting in ferroelectricity at room temperature. This study provides a design perspective for the selection of doping ions to achieve various properties in rutile-type TiO₂ ceramics.