摘要
MAKAROV and Trontelj first reported the WO<sub>3</sub>-based low voltage varistor material doped with MnO<sub>2</sub> and Na<sub>2</sub>CO<sub>3</sub> in 1994. This material is worth further study because of its low threshold voltage （ 【 10 V/mm）. We have found that the doping of Co<sub>2</sub>O<sub>3</sub> can obviously improve the nonlinearity of WO<sub>3</sub>-MnO<sub>2</sub>-Na<sub>2</sub>CO<sub>3</sub> series with nonlinear coefficient α≈ 2,and a may be higher than 5 when the amount of Co<sub>2</sub>O<sub>3</sub> is 1% （mole percentage）. However, the nonlinear characteristic almost vanished when 0.5% Al<sub>2</sub>O<sub>3</sub> was doped into this system at room temperature, and Al<sub>2</sub>O<sub>3</sub> showed very stable
