Effect of La2O3 addition on microstructure and electrical properties of ZnO-Pr6O11-based varistor ceramics

The microstructure, electrical properties, and stability of the varistor ceramics, which are composed of ZnO-Pr6O11- CoO- Cr2O3- La2O3 (ZPCCL)-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 mu A. As the La2O3 content increases, the donor concentration and density of interface states were increased from 0.64 x 10(18) to 16.89 x 10(18)/ cm(3) and from 2.21 x 10(12) to 5.16 x 10(12)/ cm(2), respectively. However, the barrier height greatly decreased with increasing La2O3 content, reaching a maximum (1.47 eV) for 0.5 mol% La2O3. (C) 2005 Springer Science + Business Media, Inc.