Low voltage TiO_2 varistors dopped with Ta_2O_5 and Cr_2O_3

摘要

Ta-Mn-Cr-doped TiO_2 varistors were investigated with the purpose to clarify the roles of the dopants over the electric properties. The structural and electrical properties were studied by using scanning electron microscopy (SEM),Ⅰ―Ⅴmeasurements and x―ray diffraction (XRD). The varistors sintered at 1400°C for 2h in air presented density values about 95% of the theoretical density. From the experimental results, it was observed that an optimum addition of Ta_2O_5 (> 0,05 mol %) leads to an improvement of the electrical characteristics, presenting a low breakdown voltage (0,15― 0,3 V per grain boundary). The non― linearity coefficient increased from 2,6 to 8 as Cr_2O_3 was added and a low voltage (0,16 V per grain boundary) was observed. X-ray diffraction analyses showed the crystalline TiO_2 rutile phase without no other phases. Therefore, low voltage Ta― Mn-Cr doped TiO_2 varistors can be produced after adequate addition of Ta_2O_5 and Cr_2O_3 with excellent varsitors properties.