Characterization of ZnO-Based Multilayer Varistor Sintered by Hot-Press Sintering

Abstract

To attain the homogeneous microstructure of ZnO-based multilayer varistors (MLVs), hot-press sintering is conducted. To determine the effect of hot-press sintering on the microstructure, the dielectric and varistor properties of ZnO-based MLVs were investigated and compared with those of ZnO-based MLVs fabricated by free sintering. In hot-press sintering, the average grain size and the distribution of grain size of a ZnO-based MLVs are both reduced. The results show that the leakage current and nonlinear coefficient ( α) of ZnO-based MLVs can be improved. The increase in nonlinear coefficient ( α) is directly related to the inhibition of grain growth of ZnO grains when hot-press sintering is performed instead of free sintering. Note that the energy absorption capabilities in terms of peak current (PC) measurements of ZnO-based MLVs are remarkably improved due to the homogeneity of microstructure when hot-press sintering is conducted.

LOW-TEMPERATURE SINTERING OF ZnO-Bi₂O₃-BASED VARISTOR CERAMICS FOR ENHANCED MICROSTRUCTURE DEVELOPMENT AND CURRENT-VOLTAGE CHARACTERISTICS

“…Temperatures below 1000°C would also enable the use of cheaper Ag contacts instead of the much more expensive Pd-or Ptcontaining ones [9][10][11][12][13][14][15]. Different approaches have been reported in order to prepare dense varistor ceramics with good I-U characteristics at temperatures below 1000°C, such as the use of fine starting powders with a high sinterability prepared by a polymerized complex method [16], a two-stage, low-temperature thermal processing [17,18], hot pressing [19] or the addition of low-melting glass frit [10,20]. They resulted in a high density of varistor ceramics; however, the breakdown voltages of the ceramics were still above 1000 V·mm -1 , which is much too high for most applications.…”