The Effect of Reducing Gases on the Conductivities of Metal Oxide Semiconductors

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Abstract
The electrical resistance of a disk of silver oxide (Ag2O) decreases enormously at room temperature when it is exposed to carbon monoxide gas. Using this effect, carbon monoxide in air can be detected selectively and quantitatively over a wide range from 10 ppm to 105 ppm. The direction of the change in resistance due to carbon monoxide is difficult to explain from a simple adsorption model of electron-donating gases on a semiconductor if Ag2O is assumed to be a p-type semiconductor. We conclude that this change can be explained by taking into account the reduction of the Ag2O surface by carbon monoxide. A similar resistance change due to carbon monoxide has been found in p-type CoO, MnO2 and NiO.