Colossal permittivity and low dielectric loss in (Li, Nb) co-doped SrTiO3 ceramics with high frequency and temperature stability

Sr(Li1/4Nb3/4)xTi(1-x)O3 (0.000 ≤ x ≤ 0.04) (STLN) ceramics were synthesized via a solid-state reaction under a flowing nitrogen atmosphere. Co-doping with Li+ and Nb5+ considerably enhanced the dielectric properties of SrTiO3 ceramics. These dielectric properties increased with the co-doping concentration x up to x = 0.012 and decreased for higher x. The STLN ceramic with x = 0.012 exhibited a colossal permittivity of εr = 17,300 (1 kHz) and an ultralow dielectric loss of tanδ = 0.017 (1 kHz), with excellent frequency (20–106 Hz) and temperature (room temperature to 450 °C) stabilities. Their dielectric relaxation mechanisms and point-defect structures were also investigated. With an excessive increase in x, the formation of point defects is inhibited, resulting in the deterioration of the dielectric properties of the STLN ceramics. Further studies showed that acceptor doping Li+ and N2 atmosphere sintering provided a large number of oxygen vacancies. These oxygen vacancies contribute to the formation of some defect dipoles and defect-dipole clusters (TiTi′−VO••−TiTi′, NbTI•−TiTi′) related to oxygen vacancies. These defect dipoles and defect-dipole clusters restrict non-localized electrons, leading to electron-pinning. Consequently, the sample exhibits colossal permittivity and low dielectric loss. In addition, a high grain boundary resistance also contributes to the reduced dielectric loss.