Acceptor doping induced oxygen vacancies enabling colossal permittivity with low dielectric loss in Al/In/Nb co-doped TiO2 ceramics

Oxygen vacancies in (Al x In 1- x ) 0.0025 Nb 0.0025 Ti 0.995 O 2 ceramics are regulated by tuning the Al 3+ /In 3+ acceptor ratio at a fixed Nb 5+ donor content. • The sample with x  = 0.4 achieves optimal dielectric performance: ultrahigh permittivity 2 × 10 4 and low dielectric loss ~0.05 over broad frequency and temperature ranges. • Al 3+ enrichment contracts the rutile lattice, reduces oxygen vacancies, and modulates Ti 3+ states and local lattice distortion. • Impedance, modulus and Arrhenius analyses verify thermally activated Ti 3+ /Ti 4+ carrier hopping and oxygen vacancy related dielectric relaxation in the ceramics. • Oxygen-vacancy dipoles and IBLC/SBLC interfacial polarization synergistically yield colossal permittivity in grain/grain-boundary heterostructures. TiO 2 -based colossal permittivity ceramics show promising potential for energy storage applications and sensing due to their superior dielectric performance and tunable defect structures. (Al x In 1− x ) 0.0025 Nb 0.0025 Ti 0.995 O 2 ceramics were fabricated via a solid-state reaction method, aiming to tailor oxygen vacancy defects through acceptor-ion substitution. With increasing Al content, the E g Raman mode exhibits a pronounced shift, indicating significant modulation of local lattice distortion and oxygen-vacancy concentration. Remarkably, the composition with x  = 0.4 an excellent balance between dielectric permittivity and loss, exhibiting a dielectric constant of ~ 2 × 10 4 and a low dielectric loss of ~0.05. Detailed impedance and modulus analyses reveal that the observed dielectric relaxation originates from thermally activated Ti 3+ /Ti 4+ hopping and oxygen vacancy related defect responses. Combined with the electrically heterogeneous microstructure consisting of semiconducting grains and insulating grain boundaries, the colossal permittivity behavior is primarily attributed to an IBLC/SBLC-related polarization mechanism. Overall, a high dielectric constant can be achieved via defect engineering and triple doping modulation, providing a viable strategy for the design of next-generation dielectric capacitors.