CONDUCTANCE EFFECTS OF AMMONIA ON SILVER-CHLORIDE BOUNDARY-LAYERS

The influence of the Lewis base NH3 on the conductivity of AgCl films is investigated. Three types of films are studied: epitaxial films on NaCl (100), polycrystalline films on sapphire, as well as 'freestanding' films. In the case of films in contact with s substrate, annealing is necessary in order to achieve equilibrium values for the conductivity even under an inert atmosphere. Two counteracting effects of NH3 are discussed: core effects due to increased transfer resistivities and space-charge effects due to an increase of the Ag+-vacancy concentration. The latter phenomenon can lead to an increase in the overall conductance, if the interstitial contribution to the total conductivity is not too large. As far as the first effect is concerned, the conductance change involved can be quantitatively correlated with the ammonia partial pressure using a simple adsorption model. The conductance response is below 5 min in the temperature range 100-170 °C (103 Pa < p(NH3) < 105 Pa) for the freestanding films and is reproducible within the limits of experimental error. © 1990.