2.27 A greatly exaggerated representation of the change in lattice parameter for cations of different sizes. (a) When the anion changes size (when co2-3 decomposes O2- CO2and CO2-, for instance) and the cation is large, the lattice scale changes by a relatively small amount. (b) if the cation is small, the relative change in lattice scale is large, and decomposition is thermodynamically more favorable.