Study On Additive-doping Effects On Microstructure And Electrical Properties Of TiO₂ Based Varistors

Ti O2 based varistors has low varistor voltage, high the nonlinear coefficient and dielectric constant of Ti O2 compared with other varistors. The preparation procedure of Ti O2 based varistors is simpler when compared with other varistors for low-voltage application. Accordingly, Ti O2 based varistors have been widely used in the electrical circuit of voltage absorbing, voltage limiting, nonlinear compensation and function transformation. The effects of doping Fe2O3、Zr O2 into Ti O2 based varistors were studied in this passage and it was found that:(1) The doping of Fe2O3 has some effect on the microstructure and electrical properties of the Ti O2-Ta2O5 based varistor ceramics. It was revealed that the doped Fe2O3 could enter into the lattice of Ti O2, and no second phase could be observed in the present samples. The measured electric-field vs current-density characteristics of the samples indicated that the nonlinear coefficient of the prepared varistors slightly decreased, and the varistor voltage increased dramatically with increasing contents of Fe2O3. For the samples doped with 0.1 mol% Fe2O3, the highest varistor voltage of 299 V/cm with the lowest non-linear coefficient of 3.6 was obtained.(2)Ti O2-Nb2O5-Cr2O3 varistors doped with different contents of Fe2O3 were notan density system with a number of pores in samples. Certain doping amount of Fe2O3 could increase the density of samples. As the doping content of Fe2O3 increased, the nonlinear coefficient first increased to 16.0 and then decreased, when the doping amount of Fe2O3 reached 2 mol%, the nonlinear property disappeared.The varistor voltage showed an increasing tendency from 5.9 V/mm to 249 V/mm. The leakage current of the doping samples were larger than the none-doped one.(3) In Ti O2-Nb2O5-Cr2O3 based varistor ceramics, the doping of Zr O2 was beneficial for decreasing the porosity of the samples. In the non-doped Ti O2-Nb2O5-Cr2O3 varistors, second phase can be observed between grains and was supposed to be Cr0.1Nb0.1O2Ti0.8. When doping amount of Zr O2 reached 2.0 mol%, no obvious second phase could be observed. When the Zr O2 doping content was no more than 1.0 mol%, the varistor voltage increased up to 11.8 V/mm with increasing doping amount of Zr O2, but decreased down to 5.1 V/mm when the doping amount of Zr O2 reached 2 mol%. As the doping amount of Zr O2 increases, the nonlinear coefficient decreased continuously from 5.7 to 3.6 and then disappeared when doping amount went 2 mol%.The leakage current showed an increasing tendency from 199 to 376 μA/cm2.