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

Sr(Li 1/4 Nb 3/4) x Ti (1- x) O 3 (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 SrTiO 3 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 ε r = 17,300 (1 kHz) and an ultralow dielectric loss of tan δ = 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 N 2 atmosphere sintering provided a large number of oxygen vacancies. These oxygen vacancies contribute to the formation of some defect dipoles and defect-dipole clusters (Ti Ti ′ − V O • • − Ti Ti ′ , Nb TI • − Ti Ti ′) 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. [ABSTRACT FROM AUTHOR]