Colossal permittivity and ultralow dielectric loss in SrTi1-xNbxO3 ceramics sintered at different atmospheres via defect chemistry improvement

Abstract

SrTiO3 is recognized as one of the most promising candidate materials for colossal permittivity. However, the origin of colossal permittivity is still not well understood. In this work, SrTi0.998Nb0.002O3 ceramics (SNT) were synthesized via typical solid-state reaction process and sintered in air, N2, and N2–H2 atmospheres (labelled as SNT-Air, SNT-N2 and SNT-H2). The SNT-H2 ceramic achieves a colossal permittivity of 89254 and a dielectric loss of 0.013 at 1 kHz and maintains a colossal permittivity (∼8 × 104) with a low dielectric loss (<0.1) throughout a wide temperature (50 °C–300 °C) and frequency (100 Hz-1 MHz) range. The mechanism of the outstanding properties of SNT-H2 ceramics was investigated by X-ray photoelectron spectroscopy (XPS), impedance spectrum and activation energy analysis. The TiTi′−VO⋅⋅−TiTi′ defect dipole and VO⋅⋅−3TiTi′−NbTi⋅ defect dipole clusters exist in SNT ceramics by sintering in the reducing atmosphere of H2. Otherwise, the grain is semi-conducting, and the grain boundary is insulating in SNT-H2 ceramics by impedance spectrum analysis. In conclusion, the defect dipole and clusters localized in the grain could be the fundamental cause for the ultra-dielectric properties. As a result, The SNT-H2 ceramic exhibits the colossal permittivity with low dielectric loss, as well as good temperature and frequency stability, potentially aiding in the development of colossal materials.