Microstructural characteristics of varistors in the ZnO-BaO-P2O5 system.

Ceramic materials based on the system ZnO-BaO show a great potential for va ristor applications. However, the BaO rich phase located at the grain bound aries shows high solubility in water which causes severe damage of the mate rials. In order to overcome this problem, doping with P2O5 to form BaZn2(PO 4)(2) and Zg(PO4)(2) has been studied. The resistance of these materials to degradation by moisture has been evaluated by lixiviation experiments. Sin tering has been followed by means of dilatometric technique and microstruct ure was analysed by Scanning Electron Microscopy, SEM. The electrical prope rties of these materials evidence a varistor behaviour similar to that obse rved for materials in the system ZnO-BaO.