Experimental and theoretical investigations on the lattice defects and sintering atmosphere tuning the colossal permittivity of SrTiO3 ceramics

Abstract

The Sr0.995La0.005TiO3 ceramics were fabricated with traditional solid-state methods under diverse sintering atmospheres. The dielectric properties have a significant correlation with the sintering atmosphere, while showing favorable temperature and frequency stability. As sintered in a mixed hydrogen-nitrogen atmosphere, Sr0.995La0.005TiO3 ceramics exhibited a colossal permittivity (ԑr ∼ 31307), low dielectric loss (tanδ ∼ 0.038) and good frequency stability synergistic temperature stability (−70 °C-180 °C, ΔC/C25°C ≤ ±15 %). The association mechanism of oxygen vacancies, lattice defects, and dielectric characteristics is evaluated in the context of experiments and first-principles. The phase structure and microstructure analysis revealed that the ceramics contained a two-phase structure with a SrTiO3 phase and a TiO2 second phase. The analysis of elemental valence and dielectric characterization demonstrated that defective dipoles, oxygen vacancies, and defect clusters resulting from non-homogeneous ion substitution are the major reasons for contributing to the colossal permittivity and low dielectric loss of the ceramics. This revealed that the electron-pinned defect dipole (EPDD) effect dominates in Sr0.995La0.005TiO3 ceramics. In addition, it can be established that the SrTiO3 phase and TiO2 phase contribute to the EPDD effect simultaneously, with SrTiO3 main phase taking the main role. According to the ELF plot analysis, when the content of oxygen vacancies is high, electrons accumulate at oxygen vacancies and defect clusters, leading to a high localization of electrons, which contributes to colossal permittivity and low dielectric loss of ceramics. The results are promising in colossal permittivity (CP) materials.