Solid state electrochemical reactions in systems with miscibility gaps

Cyclic voltammograms of electroactive solid compounds with partial immiscibility between the oxidized and reduced phases can exhibit a splitting of the peaks. If the free energy of transformation between the oxidized and reduced phases is small, the formal potentials of the redox pair will be almost the same in both solid phases. This results in an inert potential range in which no appreciable electrochemical activity is possible. The kinetic implications of this situation have been analysed in relation to the width of the miscibility gap. The diffusion of ions in the particle, which is hindered by the immiscibility, can proceed when a transition zone between the two phases exists in which the crystal structure is changed. If there is no such transition zone the voltammogram will display several spikes, which are caused by the collapse of concentration barriers at the sharp interfaces between the two phases in the mixed crystals. Received: 14 October 1999 / Accepted: 4 November 1999