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

• Published in: Ceramics international Vol. 51; no. 20; pp. 31430 - 31441
• Main Authors: Wang, Lei, Wu, Yilin, Li, Jinsheng, Li, Fengxu, Liu, Xudong, Zhang, Mu, Bi, Xiaoguo, Li, Xiaodong, Xu, Mengjia, Sun, Xudong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2025
• Subjects: Colossal dielectric constant; Defect dipoles; Doped TiO2 single crystal; Polarization mechanisms; Defect dipoles; Doped TiO2 single crystal; Colossal dielectric constant; Polarization mechanisms
• ISSN: 0272-8842
• DOI: 10.1016/j.ceramint.2025.04.332

Donor-acceptor co-doped TiO2-based materials have attracted consideration attention because of their excellent dielectric properties, however, the effect of different acceptor ions on the dielectric properties of TiO2 single crystals has been the subject of little study. In this paper, (Nb0.5A0.5)0.5 %Ti99.5 %O2 (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 TiO2 ceramic samples. In contrast, as the radius of the acceptor ion increases, the ions encounter greater difficulty in entering the TiO2 lattice. In addition to electron-pinned defect-dipole (EPDD) polarization, hopping polarization occurs in (Nb0.5Sc0.5)0.5 %Ti99.5 %O2 single crystal, while interfacial polarization occurs in (Nb0.5La0.5)0.5 %Ti99.5 %O2 and (Nb0.5Nd0.5)0.5 %Ti99.5 %O2 single crystals, both of which adversely affect the dielectric properties. In the (Nb0.5Ga0.5)0.5 %Ti99.5 %O2 single crystal, the defect clusters of triangular structure Ga23+VO··Ti3+ and diamond structure Nb25+Ti3+XTi (X = A3+/Ti3+/Ti4+) 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 × 105, 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 TiO2-based materials, thereby facilitation a more scientific design of TiO2-based giant dielectric materials.