Abstract :
The microstructure, electrical properties,
and stability against DC accelerated aging stress of the
varistor ceramics, which are composed of ZnO–Pr6O11–
CoO–Cr2O3–La2O3-based ceramics, were investigated
for various La2O3 contents. The increase of La2O3
content led to more densified ceramics, whereas
abruptly decreased the nonlinear properties by incorporating
beyond 1.0 mol%. The highest nonlinearity
was obtained from 0.5 mol% La2O3, in which the nonlinear
exponent is 81.6 and the leakage current is 0.1 lA.
As the La2O3 content increased, the donor concentration
increased in from 0.64 · 1018 to 16.89 · 1018/cm3
and the barrier height greatly decreased with increasing
La2O3 content, reaching a maximum (1.47 eV) in
0.5 mol% La2O3. The varistors doped with 0.5 mol%
La2O3 exhibited high stability, in which the variation
rates of varistor voltage, nonlinear exponent, and
leakage current were –1.14%, –3.7%, and +100%,
respectively, for stressing state of 0.95 V1 mA/150 C/
24 h.
