The admittance boundary at an Ag″>cdBr<inf>2</inf> · 4H<inf>2</inf>O interferfcae during a dehydration process

Abstract

A dehydration process of the crystallohydrate CdBr2 · 4H2O has been investigated by the method of faradaic admittance. It was shown that the change in the mechanism of electrical conductivity caused by dehydration during the heating of a sample also gave rise to a change of the type of admittance behaviour. The analysis of admittance diagrams indicates the fact that the Randless equivalent circuit, where the parallel connection between the double electric layer capacitance Cdl and the resistance of Faradaic reaction Rf is preceded by a serial bounded ohmic electrolyte resistance Rs, corresponds to an electrochemical cell. The rise of temperature caused these resistances to change in different ways. The resistance of the faradaic impedance Rf decreases most rapidly. At the dehydration temperature only an ohmic resistance Rs, a real impedance component, remained in a cell's equivalent circuit while Rf and Cdl became so small that they depended no longer on frequency. This phenomenon can be explained by the activation of considerable concentration of Cd2+ ions that can easily move and be reduced at the voltages of these measurements up to Cd. © 1986.