The origin of dielectric relaxation behavior in TiO2 based ceramics co-doped with Zn2+, W6+ ions under a N2/O2 sintering atmosphere

Abstract

Dense (Zn_0.5W_0.5)_xTi_1−xO₂ (ZWTO_x) ceramics were fabricated using a conventional solid state reaction method with sintering under a nitrogen atmosphere (ZWTO_x-N₂) and an oxygen atmosphere (ZWTO_x-O₂), respectively. Colossal permittivity (ε > 10⁴) and low loss (tan δ < 0.1) were simultaneously achieved in ZWTO_x-N₂ ceramics, and two types of dielectric relaxation behaviors observed were interpreted to be due to interface polarization and disassociation between oxygen vacancies and trivalent titanium ions, respectively. The impedance plots suggested that the ZWTO_x-N₂ ceramics are electrical heterostructures composed of semiconductor and insulator grain boundaries, which proved that the CP performance of ZWTO_x-N₂ ceramics almost originates from the internal barrier layer capacitance (IBLC) effect. In addition, a series of anomalous dielectric behaviors such as low permittivity and low frequency dispersion were observed for ZWTO_x-O₂ ceramics; polarization (P)–electric field (E) hysteresis loop curves were obtained for ZWTO_x-O₂ ceramics, and that impedance plots have shown that the ZWTO_x-O₂ ceramics display higher insulation resistivity. Density functional theory (DFT) calculations illustrated that the Zn²⁺–W⁶⁺ ion pairs are easy to form in ZWTO_x-O₂ ceramics, which causes destruction of the local lattice and thus leads to abnormal dielectric behavior. This work will provide a new strategy for defect engineering in TiO₂ and other CP materials.