Simultaneously Achieving Colossal Permittivity, Ultralow Dielectric Loss Tangent, and High Insulation Resistivity in Er-Doped SrTiO₃ Ceramics via Oxygen Vacancy Regulation

Abstract

High-performance Sr1–x Er x TiO3 (x = 0–0.014) ceramics were sintered in different atmospheres using the conventional solid-state reaction method. The phase structure and micromorphology of ceramics were analyzed using X-ray diffraction and scanning electron microscopy. Meanwhile, the Sr1–x Er x TiO3 (when x = 0.012) ceramic sintered in hydrogen attains a colossal permittivity (132 543 @1 kHz, 157 650 @1 MHz) and ultralow tan δ (0.009 @1 kHz, 0.03 @1 MHz) and has good frequency stability (20 Hz to 2 MHz) and temperature stability (−180 to 425 °C). X-ray photoelectron spectroscopy, electron paramagnetic resonance, and impedance analysis show that the colossal permittivity and ultralow dielectric loss are attributed to the defect dipoles and defect clusters [TiTi ′–VO ••–TiTi ′], [ErSr •–TiTi ′], [2ErTi ′–VO ••], and [ErSr •–ErTi ′]. The insulation resistivity is determined by the grain boundary. The dielectric properties of samples sintered in hydrogen are excellent, and then, the oxidation method is used to backfill the oxygen vacancy (VO ••), thus improving the insulation resistivity (2.8 × 1014 Ω cm) of the grain boundary. In addition, the diffusion mechanism of ceramic VO •• from low, medium, and high temperatures was studied by monitoring VO •• behavior in real time. The results reveal that the diffusion coefficient of VO •• in the grain boundary is greater than that in the grain; as a result, as the external oxygen partial pressure rises, the VO •• escapes first from the grain boundary. When the external oxygen partial pressure decreases, oxygen atoms enter the grain boundary region first and backfill oxygen vacancies.

Improving Energy Storage Properties of KNN Ceramic through Composition Modification

“…Therefore, the relaxation behavior for the ceramic mainly arises from the migration of oxygen vacancies in grain boundaries. 29 We also used the formula 2πfτ = 1 to calculate the average relaxation time τ of ceramics, 30 which was based on the Z′∼Z″ curves obtained at 500 °C, 550 °C, and 600 °C and the results are shown in Fig. 7f.…”

High insulation resistivity and low dielectric loss in (Ta, Al)‐codoped BaTiO3 colossal permittivity materials

“…Figure 6 depicts the frequency dependence of ε r and tan δ under different sintering atmospheres. The permittivity under different sintering atmospheres is significantly varied, indicating that the change in sintering atmosphere not only affects the polarization characteristics of the ceramics but also leads to a significant change in the polarization 38 . The essential factor that distinguishes the different atmospheres is the concentration of $${\mathrm V}_{\mathrm O}^{\centerdot \centerdot }$$ in the ceramic samples, which illustrates the importance of $${\mathrm V}_{\mathrm O}^{\centerdot \centerdot }$$ in the generation of CP behavior 38–40 .…”

“…The BTA0.015 ceramics sintered in N 2 not only have one to two orders of magnitude higher dielectric constants than other ceramics, but also have the lowest dielectric loss. It is suggested that the sharp increase in ε r is due to the promotion of large amounts of $${\mathrm V}_{\mathrm O}^{\centerdot \centerdot }$$ in the high‐temperature anoxic environment, where free electrons are formed in parallel with $${\mathrm V}_{\mathrm O}^{\centerdot \centerdot }$$ production 38 . The concentration of point defects and coupling into defect clusters varies due to the different content of Al 3+ ions.…”

“…38 Pu et al concluded that the level of oxygen partial pressure during sintering has an important effect in the formation of defects. 38 Ceramics prepared at low oxygen partial pressures (N 2 ) have more clusters of defective dipoles, leading to excellent dielectric properties. The possible defects in the ceramic samples during nitrogen sintering are expressed as:…”

“…It is suggested that the sharp increase in ε r is due to the promotion of large amounts of V •• O in the high-temperature anoxic environment, where free electrons are formed in parallel with V •• O production. 38 The concentration of point defects and coupling into defect clusters varies due to the different content of Al 3+ ions. By adjusting the Al 3+ ion content it is feasible to transform the internal defect state of the ceramics into an optimal state, which results in the optimal dielectric properties.…”