Structure And Electric Properties Of Donor-Acceptor Co-Doped SrTiO₃ Ceramics

SrTiO₃ is an important dielectric material with a typical ABO₃ perovskite structure at room temperature,with a high dielectric constant??_r?300?,low dielectric loss(tan??10^-3)and better dielectric strength?E_b?10kV/mm?.Numerous studies have shown that the microstructure of SrTiO₃ can be controlled by external electric field,stress or chemical doping to obtain different electrical properties.In this paper,donor-acceptor co-doped SrTiO₃ ceramics were prepared.The effects of doping ion species,doping concentration and sintering temperature on the structure and electrical properties of SrTiO₃ ceramics were analyzed,and the stable colossal permittivity and low dielectric loss of SrTiO₃ ceramics over a wide frequency range and a wide temperature range are realized.The experimental results reveal the formation of oxygen vacancies in SrTiO₃ ceramics and its effect on the properties of ceramics.The influence mechanism of different doping ions on the structure and electrical properties of SrTiO3 ceramics is illustrated.The effects of different preparation processes on the microstructure of SrTiO₃ceramics were investigated by analyzing the phase structure and surface morphology of doped SrTiO₃ ceramics.The results show that the SrTiO₃ ceramics obtained by different preparation processes are single-phase,and the doping ions successfully enter the crystal lattice of the ceramic instead of the original SrTiO₃ ions.High concentration of La³⁺-Li⁺ions doping leads to a smaller ceramic grain size,while Al³⁺-Li⁺ions doping has little effect on grain size.In addition,In addition,the grain size of both doped ceramics increases as the sintering temperature increases.By doping the SrTiO₃ ceramic with La³⁺-Li⁺ions,a stable colossal permittivity and low dielectric loss in the frequency range of 100 Hz to 10 MHz and the temperature range of 25?to 500?are obtained.The ceramic having a doping concentration of x=0.02 had a dielectric constant of 12,199 and a dielectric loss of0.031 at 25?and 1 kHz.The colossal permittivity properties of La³⁺-Li⁺ions co-doped SrTiO₃ ceramics are derived from the defect complexes formed by La³⁺-Li⁺ions in ceramics,the defect complexes has a strong confinement effect on electrons,so the ceramic has both low dielectric loss and high dielectric constant.Al³⁺-Li⁺ions co-doped SrTiO₃ ceramics did not obtain colossal permittivity,and its dielectric properties are not significantly different from those of pure SrTiO ₃ceramics.The results show that the Al³⁺-Li⁺ion doping makes SrTiO₃ ceramics have strong interfacial polarization,which is mainly due to the large conductance difference between grains and grain boundaries.The space charge at the grain boundary leads to the leakage behavior of the Al³⁺-Li⁺ion doped SrTiO₃ ceramic.In addition,the relaxation phenomenon of dielectric loss is found in both doped ceramics.The AC impedance spectroscopy analysis shows that the relaxation behavior of La³⁺-Li⁺ions co-doped SrTiO₃ ceramics is mainly attributed to the secondary ionization of oxygen vacancies and the thermal motion of oxygen vacancies,while the relaxation behavior of Al³⁺-Li⁺ions co-doped SrTiO₃ ceramics is only attributed to the thermal motion of the oxygen vacancies.