Abstract
Current (I)‐voltage (V) characteristics of porous ZnO varistors with different Bi2O3 content have been investigated in air as well as in H2‐air mixtures in the temperature range room temperature (RT)‐600°C. The I‐V characteristics measured at RT remained unchanged in the presence of H2, but the breakdown voltage clearly shifted to a lower electric field in the temperature range 400–600°C. The breakdown voltage decreased with increasing H2 concentration in air. The optimum amount of Bi2O3 for the largest decrease was found to be 1.0 mol%. Thus, ZnO varistors can be used as a new type of H2 sensor. The results presented in this study also suggest the important role of excess oxygen ions existing at the ZnO‐ZnO grain boundaries in developing the Schottky barrier as well as in the H2‐sensing mechanism of the varistors.
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