Colossal dielectric behavior of (Nb, Ga) co-doped TiO2 single crystal

Abstract

(Nb0.5Ga0.5)xTi1−xO2 (x = 0.05%,0.2%,0.5%,1%,5%) single crystals were prepared by Verneuil method. Even if the doping amount is 0.05%, the dielectric permittivity (ε′) is obviously higher than that of pure rutile TiO2 (260), reaching more than 104. As the doping amount x increase, the ε′ increases, and reaches the maximum value when x = 5%, but the dielectric loss increases correspondingly. The best dielectric performance (ε′=1.0 ×105, tanδ=0.034 under 1 kHz) is obtained when the doping amount is 0.5%. Even at 106 Hz, the dielectric loss is only 0.019, much lower than the reported ceramic samples. This may be due to the fact crystalline materials can effectively reduce defects such as grain boundary, second phase, porosity and segregation. The dielectric spectra, impedance analysis, XPS and DC bias results show that the colossal permittivity (CP) properties could be attributed to EPDD polarization. With the increase of doping concentration (>1%), the hopping polarization occurs, resulting in a slight increase in dielectric loss. These results indicate that TiO2 crystal materials with lower dielectric loss are good candidates for dielectric materials. Taking TiO2 crystal as the research object, we can have a clearer understanding of the origin of TiO2 dielectric properties and the influence of doping ion content, which is of great significance to the development of TiO2-based dielectric materials.