Composition dependence of the solid state transitions in NaNO₃/KNO₃ mixtures

The results of a detailed calorimetric study of the NaNO₃/KNO₃ phase behaviour as a function of cation composition are presented. We conclude that the λ-transition in NaNO₃ is significantly depressed and broadened by the presence of K⁺ ions. The α-β-transition in KNO₃ is similarly affected. The possibility is considered that the depression of the λ-transition by addition of solute K⁺ ions is related to random field effects on model lattice transitions involving a continuous order parameter. Some brief remarks are made to contrast the fast ordering kinetics of the λ-transition with the slow kinetics, and structural arrests, obvious in supercooling liquids.