Effect of trivalent acceptor ions size on the dielectric properties of donor-acceptor co-doped TiO2 single crystals

Donor-acceptor co-doped TiO 2 -based materials have attracted consideration attention because of their excellent dielectric properties , however, the effect of different acceptor ions on the dielectric properties of TiO 2 single crystals has been the subject of little study. In this paper, (Nb 0.5 A 0.5 ) 0.5 % Ti 99.5 % O 2 (A = Ga, Sc, La, Nd) single crystals were prepared by the Verneuil method, and their dielectric properties were investigated. It was found that the dielectric properties of co-doped single crystals do not become superior with increasing radius of the doped ions as in the case of TiO 2 ceramic samples. In contrast, as the radius of the acceptor ion increases, the ions encounter greater difficulty in entering the TiO 2 lattice. In addition to electron-pinned defect-dipole (EPDD) polarization, hopping polarization occurs in (Nb 0.5 Sc 0.5 ) 0.5 % Ti 99.5 % O 2 single crystal, while interfacial polarization occurs in (Nb 0.5 La 0.5 ) 0.5 % Ti 99.5 % O 2 and (Nb 0.5 Nd 0.5 ) 0.5 % Ti 99.5 % O 2 single crystals, both of which adversely affect the dielectric properties. In the (Nb 0.5 Ga 0.5 ) 0.5 % Ti 99.5 % O 2 single crystal, the defect clusters of triangular structure Ga 2 3 + V O · · Ti 3 + and diamond structure Nb 2 5 + Ti 3 + X Ti (X = A 3+ /Ti 3+ /Ti 4+ ) are interspersed with each other. This results in the formation of large defect dipole clusters, where EPDD polarization is the primary polarization mechanism and the optimal dielectric properties are obtained (ε′ = 1.003 × 10 5 , tanδ = 0.0342 under 1 kHz). This work contributes to a better understanding of the effects of diverse polarization mechanisms on the dielectric properties of TiO 2 -based materials, thereby facilitation a more scientific design of TiO 2 -based giant dielectric materials .