The contribution of doped-Al to the colossal permittivity properties of AlxNb0.03Ti0.97−xO2 rutile ceramics†
The search for colossal permittivity (CP) materials continues to attract considerable interest motivated by not only academic research but also potential applications. Very recently, CP with low dielectric loss was reported in In + Nb co-doped rutile TiO2 polycrystalline ceramics. However, the mechanism of CP in this material system and the effect of doping ions are still unclear. Here, we investigated the dielectric properties of AlxNb0.03Ti0.97−xO2 (x = 0, 0.01, 0.03 and 0.05) ceramics. CP with low dielectric loss was found in AlxNb0.03Ti0.97−xO2 samples (x ≤ 0.03). Once the amount of Al-doping exceeds Nb, the CP disappears. The change in dielectric response with varying Al-doping concentration and Ti3+ concentration together with the conductive activation energy in AlxNb0.03Ti0.97−xO2 ceramics clearly suggest that the CP mechanism in co-doped TiO2 ceramics could be attributed to the internal barrier layer capacitor effect. We believe that our research provides comprehensive guidance for the development of CP materials.