Preparation And Mechanisms Of(A_1/3Ta_2/3)_x Ti_1-x O₂?A=Ca,Sr,Ba?ceramics With Colossal Permittivity

With the development of miniaturization,integration and high performance of electronic devices,colossal permittivity?CP?materials with high dielectric constant,low dielectric loss,and good frequency and temperature stability has been increasingly studied.Recently,donor Nb element and acceptor In element co-doped TiO₂ ceramics exhibit good dielectric properties,which possess colossal electric constant 104 the wide frequency range,dielectric loss was as low as 0.05,and the dielectric properties are relatively stable over a broad temperature range from 100 to 400 K.Due to the excellent performance of co-doped TiO₂ ceramics,it has become a reseach focus in the field of giant dielectric.However,the giant dielectric mechanism,the influence of preparation process and different doping ion combinations on the dielectric properties of the system is still unclear.It is of great significance to systematically study the micro-morphology,dielectric properties and mechanism of co-doping TiO₂ ceramics.In this paper,the second main group element?Ca,Sr,Ba?and Ta element co-doped TiO₂ ceramics were prepared by the traditional solid-phase method.The microstructure and dielectric properties of co-doped TiO₂ ceramics were studied.Firstly,?Ca,Ta?co-doped TiO₂ ceramics were successfully prepared by traditional solid phase method.The effects of different components on their crystal structure,morphology and dielectric properties were investigated.The sample with the high desity were got at sintered at 1400°C about 4h.As the amount of doping increases,the dielectric constant increases first and then decreases,while the dielectric loss decreases first and then increases.(Ca_1/3Ta_2/3)_x Ti_1-xO₂ ceramic with x=3% shows the high dielectric constant??r =2.1×105?and low dielectric loss?tan? = 0.15?.The nonlinear coefficient is up to 7.3,the leakage current is as low as 124?A,and the threshold voltage is 3.02V/mm.Through XPS analysis,it is found that Ta doping causes electrons to be generated inside the material,Ca doping contributes to the generation of vacancies,and the generated defect dipole cluster contributes to the improvement of dielectric properties.Secondly,considering that the larger ionic radius will produce larger defects,so the dielectric properties can be improved.we choose the Sr element of the same main group as Ca and the Ta co-doped TiO₂.By testing the dielectric properties,the dielectric properties of(Sr_1/3Ta_2/3)_x Ti_1-xO₂ ceramics are significantly improved.As the amount of doping increases,the dielectric constant increases first and then decreases,while the dielectric loss decreases first and then increases.A giant permittivity??r?3.2×105?and a low dielectric loss?tan??0.12?were observed for x=3% at 1 k Hz.The temperature stability coefficient is-10.56%¹1.4%,and the overall stability stability coefficient is better than that of(Ca_1/3Ta_2/3)_x Ti_1-xO₂ ceramics,which has met the needs of electronic devices.XPS energy spectrum analysis showed that with the increase of doping amount,the content of Ti3+ increased,while the content of oxygen vacancies gradually decreased,mainly because the electrons trapped by oxygen vacancies were confined in the crystal lattice,and there was a defect complex inside the material.Finally,Ba with larger ionic radius and Ta are selected to improve dielectric properties by producing larger defects.The results show that the dielectric properties of?Ba1/3Ta2/3?x Ti_1-xO₂ ceramics are worse than(Ca_1/3Ta_2/3)_x Ti_1-xO₂,(Sr_1/3Ta_2/3)_x Ti_1-xO₂ ceramics.As the amount of doping increases,the dielectric constant increases first and then decreases,while the dielectric loss decreases first and then increases.When x=7%,the dielectric constant is 2.4 × 105,and the dielectric loss is 0.2.It was found that the decrease in dielectric properties may be related to the content of second phase by XRD and SEM.Through XPS analysis,compared with the same doping amount of(Sr_1/3Ta_2/3)_x Ti_1-xO₂ ceramics,the content of Ti3+ and oxygen vacancies is significantly reduced,mainly because the radius of Ba ions is too large,resulting in the formation of the second phase,Instead of forming a replacement solid solution.The content of defects is not proportional to the ionic radius.Appropriate ionic radius can simultaneously achieve high dielectric constant and low dielectric loss.