Colossal permittivity and ultralow dielectric loss in SrTi_1-xNb_xO₃ ceramics sintered at different atmospheres via defect chemistry improvement

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, SrTi_0.998Nb_0.002O₃ 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 Ti_Ti^′−V_O^⋅⋅−Ti_Ti^′ defect dipole and V_O^⋅⋅−3Ti_Ti^′−Nb_Ti^⋅ 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.