Effect of Na2O and B2O3 Addition on Nonlinear Electrical Properties of WO3-Based Capacitor–Varistors

WO3-based varistors with added Na2O and B2O3 were synthesized by the solid-state reaction. The undoped and B2O3-doped WO3 ceramics exhibited weak nonlinear I–V characteristics. The nonlinear I–V characteristics of the ceramics increased slightly after the addition of Na2O and more significantly after the addition of Na2O and B2O3. The nonlinearity coefficients α of the WO3, Na0.005WO3, and Na0.005WO3–5 wt % B2O3 ceramics were 1.86, 2.03, and 5.22, respectively. The breakdown voltages of the WO3, Na0.005WO3, and Na0.005WO3–5 wt % B2O3 ceramics were 1.56, 6.05, and 12.42 V/cm, respectively. The dielectric constant and the dielectric loss of the Na0.005WO3–5 wt % B2O3 ceramic were ~50–150 and less than 0.3, respectively, for frequencies ranging from 1 to 1000 kHz.