| The electrical properties of zinc oxide varistors were examined during and after heat treatments using AC impedance spectroscopy and DC electrical conductivity techniques.; Impedance spectroscopy and DC electrical conductivity measurements were conducted in situ for a simple (1-x)ZnO {dollar}{lcub}cdot{rcub}x rm Bisb2Osb3{dollar} varistor system with {dollar}0le xle 0.05{dollar} to gain an understanding of the solid- and liquid-state sintering kinetics over the range {dollar}rm 600le T(spcirc C)le 1100.{dollar} Compositions with {dollar}x < 0.002{dollar} retarded sintering, whereas compositions with {dollar}x > 0.004{dollar} accelerated sintering above the eutectic temperature of {dollar}740spcirc{dollar}C. The results were interpreted in terms of limited solid solubility of {dollar}rm Bisb2Osb3{dollar} in ZnO at {dollar}x {lcub}buildrel{lcub}sim{rcub}over{lcub}={rcub}{rcub} 0.004pm 0.002,{dollar} solid state-sintering in the subsolidus, and liquid-state sintering above the solidus. A phase diagram for the ZnO-rich end of the system is proposed, based on these results.; The electrical properties of the ZnO grain boundaries were studied for post-processed Matsuoka varistor samples sintered at {dollar}1200spcirc{dollar}C from {dollar}rm 0le t(h)le 6.5{dollar} using two-point AC impedance spectroscopy and four-point pulsed DC electrical measurements. Conditions, such as measurement temperature and contact choice, are very important parameters for accurately measuring the varistor samples. A two-state grain boundary varistor model is proposed for the experimental impedance results. |
