The electrical properties and d.c. degradation characteristics of Dy2O3 doped Pr6O11-based ZnO varistors

The electrical properties and degradation of Pr6O11-based varistors, which are composed of ZnO–Pr6O11–CoO–Dy2O3 systems, were investigaed with Dy2O3 content. Highly densified ceramics sintered at 1350°C were obtained by doping with 0.5 mol% Dy2O3, reaching 97% of theoretical density. The addition of Dy2O3 to the ternary system ZnO–Pr6O11–CoO greatly improved the V–I characteristics in terms of with and without Dy2O3 addition. The stability of varistors sintered at 1350°C was far higher than that at 1300°C. The varistors with 0.5 mol% Dy2O3 showed excellent stability as well as relatively good nonlinear V–I characteristics, which are 37.8 in the nonlinear exponent and 5.4 μA in the leakage current. Their variation rate of varistor voltage was −1.7% even under very severe stress (0.80 V1 mA/90°C/12 h)+(0.85 V1 mA/115°C/12 h)+(0.90 V1 mA/120°C/12 h)+(0.95 V1 mA/125°C/12 h).