Giant dielectric permittivity and electronic structure in (Al + Sb)co-doped TiO2 ceramics

• Sintering temperature had a great influence on microstructure of ASTO ceramics.
• ε′ of ASTO ceramics was significantly reduced as the mean grain size increased.
• The existence of Al atom and O vacancy caused creation of defect-dipole moments in the TiO2 structure.

Dielectric properties of (Al + Sb) co-doped TiO2 (ASTO) ceramics prepared by a solid state reaction method were investigated. It was found that sintering temperature had a remarkable influence on the microstructure of ASTO ceramics. The mean grain size largely increased with increasing sintering temperature from 1300 to 1500 °C. Interestingly, the dielectric permittivity of ASTO ceramics was significantly reduced from 6572 to 454 at 102 Hz as the mean grain size increased. Therefore, the primary contribution to the observed high dielectric response in ASTO ceramics is not related to the internal barrier layer capacitor effect. The charge analysis revealed that the existence of both Al and O vacancy caused creation of defect-dipole moments in the TiO2 structure. Similarly, the Sb atoms could also generate the charge trapping in this structure. Consequently, high dielectric response in the ASTO ceramics is significantly enhanced in comparison to the un-doped TiO2 ceramic.

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