H₂ Sensing Properties of Metal Oxide Semiconductors as Varistor-Type Gas Sensors

Abstract

Current-voltage characteristics of semiconductive oxides have been investigated in air and in H₂ balanced with air at elevated temperatures. A shift in breakdown voltage to a high electric field was observed for Cr₂O₃, which is a typical p-type semiconductor, upon exposure to H₂, while n-type semiconductors exhibited a reverse shift in breakdown voltage. Among oxide specimens, Nb₂O₅ was found to be the most excellent candidate for a varistor-type sensor, being accompanied with high H₂ sensitivity, excellent mechanical strength and good resistance to high electric field. Further investigations have revealed that the H₂ sensing properties of Nb₂O5 could be improved by 1.0mol% Bi₂O₃ doping. Newly formed Bi₂Nb₁₀O₂₈ phase was suggested to play an important role in enhancing breakdown voltage in air and then the H₂ sensitivity.