xTi1-xO2 Ceramics Research Articles

Origin of giant permittivity in Ta, Al co-doped TiO2: Surface layer and internal barrier capacitance layer effects

In order to achieve optimized electric properties, Ta, Al co-doped TiO2 was researched by carefully tuning the composition of ceramics in this work. X-ray diffraction patterns and Raman spectra co-evidenced that all samples were in pure tetragonal rutile TiO2. (Al0.5Ta0.5)0.08Ti0.92O2 ceramics showed relatively good dielectric properties including a colossal permittivity (CP) over 104, a low dielectric loss (0.05) and a good temperature stability. Especially, physical origins of giant permittivity were explored by a combined analysis of impedance spectroscopy, XPS and reflection spectra. Impedance and modulus spectrum verified three relaxation peaks indicating the electronic heterogeneity of materials. Combined with nonlinear I-V behavior, it can be concluded that the origin of the CP was attributed to the internal barrier layer capacitance (IBLC) effect. In addition, based on the results of XPS and reflection spectra, significant changes of oxygen vacancy and Ti3+ concentration were observed for the samples with different thickness, which further proved the contribution of surface layer effect to low-frequency dielectric response. Finally, the CP of (Al0.5Ta0.5)xTi1-xO2 ceramics were attributed to a synergy effect of the IBLC and surface layer effect.

Dielectric properties of (Bi0.5Nb0.5)xTi1-xO2 ceramics with colossal permittivity

The (Bi0.5Nb0.5)xTi1-xO2 (BNTO, 0 ≤ x ≤ 0.05) ceramics were synthesized by a standard conventional solid-state reaction. The effects of sintering temperature and composition x on the crystal structure, microstructure, and dielectric properties of BNTO ceramics were investigated. A pure rutile phase is achieved as x ≤ 0.01, and secondary phase Bi1.74Ti2O6.624 is detected as x ≥ 0.025. BNTO ceramic with x = 0.025 shows a high dielectric constant (155.1 k) and low dielectric loss (0.042) at 1 kHz (room temperature). Colossal permittivity is primarily related to Maxwell-Wagner effect, electron-pinned defect-dipoles or weak-binding electron. The low dielectric loss is argued to Bi ions which are doped into TiO2 lattice and the formation of Bi1.74Ti2O6.624 phase.

Preparation, characterization, and giant dielectric permittivity of (Y3+ and Nb5+) co–doped TiO2 ceramics

The microstructure and giant dielectric properties of Y3+ and Nb5+ co–doped TiO2 ceramics prepared via a chemical combustion method are investigated. A main rutile–TiO2 phase and dense ceramic microstructure are obtained in (Y0.5Nb0.5)xTi1-xO2 (x=0.025 and 0.05) ceramics. Nb dopant ions are homogeneously dispersed in the microstructure, while a second phase of Y2O3 particles is detected. The existence of Y3+, Nb5+, Ti4+ and Ti3+ as well as oxygen vacancies is confirmed by X–ray photoelectron spectroscopy and X–ray absorption near edge structure analysis. The sintered ceramics exhibit very high dielectric permittivity values of 104–105 in the frequency range of 40–106Hz. A low loss tangent value of ≈0.08 is obtained at 40Hz. (Y0.5Nb0.5)xTi1-xO2 ceramics can exhibit non–Ohmic behavior. Using impedance spectroscopy analysis, the giant dielectric properties of (Y0.5Nb0.5)xTi1-xO2 ceramics are confirmed to be primarily caused by interfacial polarization.