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.