Influence of surface acceptor–donor couples on conductivity and other electrochemical properties of nonstoichiometric NiO at 200 °C

Nonstoichiometric nickel oxide, a p-type semiconductor, was tested at 200 °C as an electrode material for proton conductor-based sensors. When measured in air, its potential was found to be dependent on variable concentrations of oxidisable gaseous species, and conversely, at fixed concentrations of the latter compounds the potential was dependent on the pressure of the oxygen. The potential variations, due to changes in surface hole concentrations, induced us to measure the conductivity of the oxide under the same conditions, i.e. in the presence of a donor–acceptor couple. The results obtained were in agreement with the previous observations. A kinetic model for steady state surface hole concentration is proposed to explain the above electrochemical properties.