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 μA. As the La₂O₃ content increases, the donor concentration and density of interface states were increased from 0.64×10¹⁸ to 16.89×10¹⁸/cm³ and from 2.21×10¹² to 5.16×10¹²/cm², respectively. However, the barrier height greatly decreased with increasing La₂O₃ content, reaching a maximum (1.47 eV) for 0.5 mol% La₂O₃.