Study On Preparation And Properties Of SrTiO₃-based Giant Permittivity Ceramics

The search for new high-performance dielectric materials,exhibiting temperature-and frequency-stable,colossal permittivity as well as sufficiently low dielectric loss,continue to arouse considerable interest motivated by their myriad device miniaturization and high-energy-density storage application.SrTiO₃ ceramics have really low dielectric loss,but its permittivity is only about 300,which restrict its applications in DRAM and high dielectric capacitor.So this paper takes SrTiO₃ as the study material and improves the dielectric properties of SrTiO₃ by donor/acceptor doping as well as co-doping.SrNb_x Ti_1-xO₃（SNT）ceramics were prepared via a traditional solid state reaction method and sintered in nitrogen atmosphere at 1530℃.N₂-SNT6 ceramics exhibit a giant permittivity of about 59191 and low dielectric loss of 0.023 measured at room temperature and 1 kHz,which is better than that of SNT ceramics sintered in oxygen atmosphere.With the increase of Nb content,the dielectric loss Peak 1 appeared between 10¹00 kHz was enhanced and permittivity decreased obviously,dielectric loss Peak 1 was attributed to electrons hopping between polyvalent ions.Research showed that the distribution of elements and electrical response between grain and grain boundary of N₂-SNT ceramics was homogeneous,which meant that the interfacial polarization was not the main reason for the giant permittivity response.But permittivity of SrAl_yTi_1-yO₃（SAT）ceramics sintered in nitrogen atmosphere was below 300,the introduction of Al reduced the permittivity and dielectric loss at the same time.The dielectric properties of all doped SAT samples kept stable in the range of 25²50℃,the obvious interfacial polarization was found between grain and grain boundary.Sr(Nb_0.5Al_0.5)_zTi_1-zO₃（SNAT）ceramics sintered in air exhibited a high permittivity of 8078 and relatively low dielectric loss of 0.032 when the doping amount was 10mol%,the relaxation Peak A and Peak B with activation energy of0.692⁰.707eV and 0.933eV were attributed to two stage ionization of oxygen vacancies and movement of fully ionized oxygen vacancies respectively.No obvious interface polarization was found between grain and grain boundary.The XPS results indicated that the introduction of Nb⁵⁺would be the likely reason for the partial reduction of Ti⁴⁺to Ti³⁺(Ti⁴⁺?e)in N₂-SNT and air-SNAT ceramics,then Ti³⁺and fully ionized oxygen vacancies caused by oxygen-poor sintering environment or acceptor Al doping formed[Ti⁴⁺?e-V_O^··-Ti⁴⁺?e]defect-dipoles,in which the electrons were bound by Ti⁴⁺andV_O^··,leading to the giant dielectric response in N₂-SNT and air-SNAT ceramics.