IMPEDANCE SPECTROSCOPIC INVESTIGATION OF THE INTERFACE SILVER-HALIDE OXIDE - DETECTION OF AN IONIC DEPLETION LAYER

For the first time a single ionic space-charge layer in the system ionic conductor/oxide is detected and investigated with impedance spectroscopy. The interface between silver halide (AgCl, AgBr) single crystals and electronically conducting oxides (Fe3O4, La0.5Sr0.5CoO3, RuO2, and NbO2.5-x) is investigated under conditions where, according to the model of "heterogeneous doping," a poorly conducting depletion layer (with respect to the silver ions) is expected. Besides the bulk response (i), and besides processes which are caused by incomplete contact (ii), and by Wagner-Hebb polarization (iii), an additional semicircle appears in the impedance spectra which is not observed when Pt-electrodes are used, and which is attributed to the depletion region. The absolute value of the capacitance, its temperature dependence, and the temperature dependence of the resistivity part are shown to be in line with the underlying model. The bias dependence of the response is complex, chiefly due to the superposition of space-charge and volume (Wagner-Hebb) polarization. The results are compared with those of analogous investigations of the AgX/metal electrode (Ag, Pt) interface.