Influences of lithium on the defect structures and electrical properties of ZnO–Bi₂O₃ based varistors

The role of alkali metal elements in ZnO varistor is of interest because of the small ion radius and valence state. They are expected to form acceptor state and convert the n-type ZnO grain to p-type. However, researches to manufacture p-type ZnO semi-donductor by using alkali metal elements have failed. In the present work, the effects of lithium element on the defect structures, microstructures and corresponding electrical performances of ZnO varistors is investigated. According to the obtained results, the influences of lithium element on the defect structures of ZnO varistors will vary with the amount of lithium. Lithium ion occupies the interstitial site of ZnO grain at first and then occupies the substitutional site. Trace amount of lithium (0.0005–0.002 wt%) can reduce the residual voltage of ZnO varistors while the E–J characteristics at low current region remain stable.