| varistor ceramics, a new composite semiconductor devices with capacitance and varistor function, has excellent nonlinear characteristics, high dielectric constant. TiO2 varistor ceramics is easy to implement low voltage by the simple single sintering process in the air. It is used widely in the field as low voltage protection and surge absorption components for its excellent electrical performance.In order to obtain good electrical properties of TiO2 varistor ceramics, experiments are often used in the form of doping to improve the electrical properties of TiO2 varistors, which led to the material system appear second phase, the second phase with the formation and doping elements, the amount of doping, sintering process and other work-related sample preparationThe influence of material properties and the formation principle of the second phase in La, Nb and co-doped TiO2 pressure-sensitive ceramic system were focused on in This paper. In the certain preparation process, the phase of the system was characterized by the phase diagram and XRD, the microstructure was detected by SEM,The grain and interface of the crystals, the content and distribution of the second phase elements were measured by EDS,what show the reason of the second phase formation is segregation of doping elements. The electronic of pure structure second phase was simulated by castep module in Materials studio software. The potential high of La, Nb and co-doped TiO2 pressure-sensitive ceramic was calculated by CASTEP,what show the doping content and variation trend of the potential high. The results show that:(1) the second phase exist in La and co-doped TiO2 pressure-sensitive ceramic. La is easy to segregate and form the second phase, La4Ti9024 is formed in La doped TiO2 pressure-sensitive ceramic; the second phase change LaNbO4 to LaNbTiO6 with sintering temperature increasing in co-doped TiO2 pressure-sensitive ceramic,and they are La4Ti9O24,LaNbO4 and LaNbTiO6; there is no second phase in Nb doped TiO2 pressure-sensitive ceramic.(2) The forming mechanism of the second phase was analysised according to the test results, phase diagram and the constants of the crystalline structure. the second phase will exhalate at interface in order to reduce the interface energy because of the second phase and the original phase forming the coherency interface with high energy.(3) The electrical properties of TiO2 pressure-sensitive ceramic is effected by the second phase. The high pressure sensitive voltage and nonlinear coefficient are in La doped pressure-sensitive ceramic, the minimum V1mA is 110.94 V/mm, nonlinear coefficient is about 28.2; The lower pressure sensitive voltage and nonlinear coefficient are in Nb doped pressure-sensitive ceramic, the V1mA is 3-5V/mm, nonlinear coefficient is 2-4; The low pressure sensitive voltage and nonlinear coefficient are in co-doped pressure-sensitive ceramic, the V1mA is 2-5V/mm, nonlinear coefficient is 3-4.(4) The single structure LaNbO4 in samples is tested by XRD,and the pure single LaNbO4 is insulator. The orthogonal structure LaNbTiO6 in samples is tested by XRD, and the pure orthogonal LaNbTiO6 is insulator. Pure La4Ti9024 is four structure, have relative small forbidden band width (< 3eV).(5) Barrier heightΦB increase with the content of Nb increasing,When the Nb atoms percentage is in 0%-2%, barrier heightΦB is round 0.5 ev in fluctuation. When x (Nb2O5) change 0 to 1%, the height of potential was less influenced by Nb. Barrier heightΦB increase with the content of La increasing in La doped TiO2 pressure-sensitive ceramic. In co-doped TiO2 pressure-sensitive ceramic barrier heightΦB increase with the content La increasing when the concent of Nb is 1at% constantly in the grain and interface of the crystals... |
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