Giant dielectric permittivity and electronic structure in (A3+, Nb5+) co-doped TiO2 (A = Al, Ga and In)

Abstract The dielectric properties of (A 3+ , Nb 5+ ) co-doped TiO 2 (A = Al, Ga and In) ceramics prepared by a solid state reaction method were studied. Sintered (A 3+ , Nb 5+ ) co-doped TiO 2 ceramics with A = Al and Ga were found with a dense ceramic microstructure. Besides the internal barrier layer and surface barrier layer capacitor effects, the formation of electron pinned defect dipoles at a specific region may have probably an influence on the dielectric response in these co-doped TiO 2 ceramics doping with different A 3+ dopants (A = Ga and In). All of the sintered ceramics exhibited giant dielectric permittivity ranging from 10 3 –10 4 and low loss tangent (tanδ≈0.05 at 1 kHz). To understand the cause of large dielectric permittivity in these materials, the theoretical modellings based on density functional theory were carried out. Our calculation results revealed that triangular shape of A 2 V O Ti (V O =oxygen vacancy) was found in (A 3+ , Nb 5+ ) co–doped TiO 2 with A = Ga and In. Moreover, the diamond shape of 2 Nb doped TiO 2 was observed to be the most preferable configuration. These shapes may generate large defect-dipole clusters in this structure and hence, the dielectric constants are dramatically improved.