Solid state electrochemical reactions in systems with miscibility gaps

Cyclic voltammograms of electroactive solid compounds with partial immiscib ility between the oxidized and reduced phases can exhibit a splitting of th e peaks, If the free energy of transformation between the oxidized and redu ced 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 imp lications of this situation have been analysed in relation to the width of the miscibility gap. The diffusion of ions in the particle. which is hinder ed 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 su ch transition zone the voltammogram will display several spikes, which an c aused by the collapse of concentration barriers at the sharp interfaces bet ween the two phases in the mixed crystals.