Polarization Effects in the Ionic Conductivity of Silver Bromide

Abstract

Alternating current impedance measurements on samples of silver bromide with silver and with gold electrodes show the presence of polarization effects. These effects appear as a capacitive component of the impedance and a slight dependence of the resistance on the frequency of the measurement, and their dependence on temperature, frequency, pressure, voltage, and impurity content has been investigated. A macroscopic theory is developed to describe the motion of the mobile charge carriers (ionic defects) which exist in AgBr at elevated temperatures. The general equations contain the effects of conduction and diffusion currents, space charge, and formation and recombination. Since these equations are nonlinear, an approximation procedure is developed, which is valid for small values of the applied voltage. The results of the theory with appropriate boundary conditions give semiquantitative agreement with the temperature and frequency dependence of the observed results and afford a good qualitative description of all of the observed effects. It is concluded that Frenkel defects are responsible for the polarization effects and that the formation and recombination rate is smaller than might at first be expected.