Effect of sintering temperature on electrical properties and stability of Pr6O11-based ZnO varistors

The electrical properties and stability of ZPCCE varistors, which are composed of ZnO-Pr6O11-CoO-Cr2O3-Er2O3-based ceramics, were investigated as a function of sintering temperature and time in the range of 1325-1345 degreesC for 1-2 h. As the sintering temperature and time increased the nonlinear exponent decreased, whereas the leakage current was improved, and overall, its stability was also improved. Among all ZPCCE-based varistors, the varistors sintered at 1335 degreesC for 1 h exhibited the highest nonlinearity, with a nonlinear exponent of 70.53 and a leakage current of 1.92 muA, but revealed comparatively low stability. The varistors sintered at 1340 degreesC for 2 h, with a nonlinear exponent of 43.37 and a leakage current of 1.18 muA, exhibited the highest stability, in which the variation rates of the varistor voltage, nonlinear exponent, leakage current were -1.54%, -2.49%, and +240.68%, respectively, under continuous DC stress, such as (0.80 V-1mA/90(degrees)C/12h)+(0.85 V-1mA/ 115(degrees)C/12h)+(0.90 V-1mA/120degreesC/12h)+(0.95 V-1mA/125degreesC/12h)+(0.95 V-1mA/150(degrees)C/12h). These varistors will be usefully applied to surge protectors in the future. Conclusively, it was found that the electrical properties and stability of ZPCCE varistors are strongly affected by the sintering temperature and time. (C) 2002 Kluwer Academic Publishers.