HYDROGEN-SENSING MECHANISM OF ZINC-OXIDE VARISTOR GAS SENSORS

The hydrogen-sensing properties of ZnO varistors have been investigated as a function of their Cr2O3 content. The addition of an appropriate amount of Cr2O3 results in an enhancement of the H-2 sensitivity, since a relatively large shift in the breakdown voltage towards the direction of a low electric field is observed in the presence of H-2. The results presented in this study strongly suggest the important role of excess oxygen ions existing at ZnO-ZnO grain boundaries in both the H-2 - sensing mechanism and in the formation of a double Schottky barrier, the latter being responsible for the nonlinear I-V characteristics of the varistors.