High-performance colossal permittivity for textured (Al+Nb) co-doped TiO2 ceramics sintered in nitrogen atmosphere

Giant dielectric response and relaxation behavior of Bi3+/W6+ co-doped TiO2 ceramics

With the rapid development of electronic information technology, dielectric ceramics are widely used in the field of passive devices such as multi-layer ceramic capacitors. In this paper, (Bi2/3W1/3)xTi1-xO2 (BWTOx) ceramics with superior dielectric properties have been prepared by using a traditional solid-state method. Remarkably, at a (Bi2/3W1/3)4+ doping level of 0.01, a (Bi2/3W1/3)0.01Ti0.99O2 ceramic achieved a giant dielectric permittivity of ∼1.5 × 104 and a low loss tangent of ∼0.07 at 1 kHz, as well as a good temperature independence, which could satisfy the operating temperature standards for X9R capacitors. The abnormal dielectric relaxation in the low temperature region can be explained by the interface polarization. Data based on the complex impedance spectroscopy and X-ray photoemission spectroscopy results indicate that the colossal permittivity of BWTOx ceramics is mainly ascribed to the internal barrier layer capacitance effect. The findings of this work could provide valuable insights for achieving large dielectric constants and good temperature stability simultaneously in BWTOx and other related electronic ceramic materials.

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

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.

Ultrahigh dielectric permittivity in oxide ceramics by hydrogenation

Boosting dielectric permittivity representing electrical polarizability of dielectric materials has been considered a keystone for achieving scientific breakthroughs as well as technological advances in various multifunctional devices. Here, we demonstrate sizable enhancements of low-frequency dielectric responses in oxygen-deficient oxide ceramics through specific treatments under humid environments. Ultrahigh dielectric permittivity (~5.2 × 10⁶ at 1 Hz) is achieved by hydrogenation, when Ni-substituted BaTiO₃ ceramics are exposed to high humidity. Intriguingly, thermal annealing can restore the dielectric on-state (exhibiting huge polarizability in the treated ceramics) to the initial dielectric off-state (displaying low polarizability of ~10³ in the pristine ceramics after sintering). The conversion between these two dielectric states via the ambient environment-mediated treatments and the successive application of external stimuli allows us to realize reversible control of dielectric relaxation characteristics in oxide ceramics. Conceptually, our findings are of practical interest for applications to highly efficient dielectric-based humidity sensors.