Colossal Permittivity Properties And Mechanism Of The Acceptor And Donor Ions Co-doped TiO₂-based Ceramics

The novel donor acceptor co-doped(A_（4-5n）/3B_n)_xTi_1-xO₂ colossal permittivty material systems are expected to be applied in the field of high energy storage,for its excellent comprehensive dielectric properties.However,the research of the systems is still in its infancy,and the polarization mechanism of the colossal permittivty is not yet clear,which limits the further improvement of its dielectric properties.Therefore,on the basis of broadening the(A_（4-5n）/3B_n)_xTi_1-xO₂ material systems,it is urgent to study the polarization mechanism of(A_（4-5n）/3B_n)_xTi_1-xO₂ material systems systematically and to find out the influence of different polarization modes on dielectric properties,so as to lay a theoretical foundation for the preparation of better colossal permittivty materials.The main research contents are as follows:（1）In order to solve the problem that the polarization mechanism of(A_（4-5n）/3B_n)_xTi_1-xO₂ systems is not clear,the(La_0.5Nb_0.5)_xTi_1-xO₂ ceramics were prepared by using A=La³⁺and B=Nb⁵⁺as donor and acceptor ions respectively.The ceramics were characterized by SEM,XRD,impedance spectroscopy,DC bias,XPS,wide temperature dielectric spectrum and polarization activation energy.The results show that the polarization mechanism of the systems is consisting of the electron-pinned polarization,hopping polarization and interfacial polarization.The experimental results show that the 3%LNTO ceramic has the best dielectric properties:ε=49692,tanθ=0.02896.（2）On the basis of the above studies,in order to further analyze the mechanism of different polarization modes on the dielectric properties,the(La_0.5Ta_0.5)_xTi_1-xO₂（LTTO）and(Er_0.5Ta_0.5)_xTi_1-xO₂（ETTO）ceramics were prepared.Through systematic analysis of the test results,the research shows that Ta⁵⁺ion can enhance the electron-pinned polarization instead of Nb⁵⁺ion,and the high doped La³⁺and Er³⁺ions can highlight the interfacial polarization and hopping polarization respectively,which not only verify the above polarization mechanism,but also explore the effect of different polarization modes on dielectric properties.The results show that the dielectric properties of(A_（4-5n）/3B_n)_xTi_1-xO₂ ceramics are deteriorated by excessive interfacial polarization and hopping polarization.Only when the electron-pinned polarization plays a major role,can the(A_（4-5n）/3B_n)_xTi_1-xO₂ ceramics achieve colossal permitivity with low dielectric loss,reflected in the 1%ETTO ceramics which the electron-pinned polarization plays a major role,achieving both colossal permitivity and ultra-low dielectric loss:ε=36194,tanθ=0.0088.（3）Based on the above results,(Nd_0.5Ta_0.5)_xTi_1-xO₂（NTTO）ceramics were prepared to further improve the permitivity and obtain lower dielectric loss.By adjusting the co-doped ratio,with the experiments of dielectric properties,impedance spectroscopy and fitting polarization activation energy,the results show that the polarization mechanism of 1%NTTO ceramics is mainly contributed by electron pinning polarization,showing excellent dielectric properties:not only the dielectric loss is further reduced but also the permitivity is greatly increased:ε=0.0076,tanθ=82052,which is much higher than the permitivity of the existing ultra-low loss(A_（4-5n）/3B_n)_xTi_1-xO₂ systems,laying the material foundation for the industrial production of energy storage capacitors.