Synthesis and characterization of (sm, Al) co-doped SrTiO₃ with giant dielectric constant and low dielectric loss through defect engineering design

Sr_0.975Sm_0.025Ti_1−xAl_xO₃ (x = 0, 0.005, 0.01, 0.015, 0.02, 0.025) ceramics were synthesized via solid-state reaction. The sample with an x = 0.005 doping concentration exhibited the optimal dielectric properties, with an electric constant of 8832 and a dielectric loss of tanδ = 0.019, measured at 1 kHz and room temperature. This sample also exhibited excellent frequency stability (ranging from 100 Hz to 1 MHz) and temperature stability (from room temperature to 200 °C). The activation energy calculation for the dielectric modulus relaxation peak, coupled with XPS results, indicates that in the sample with x = 0.005, there is a significant presence of oxygen vacancies and Ti³⁺ ions, which form defect complexes (Ti³⁺− \(V_O^{..}\) $V_O^{..}$ −Ti³⁺). These complexes restrict the delocalization of electrons, leading to electron pinning. Consequently, the sample demonstrates a high electric constant and low dielectric loss. In addition to the defect complexes, high grain boundary resistance reduces dielectric loss and enhances temperature stability. The findings of this study offer crucial conceptual insights for the defect engineering of complex perovskite materials, facilitating the development of doped strontium titanate ceramics with colossal permittivity.