Strong hysteresis near solidification points of alkali halides with high ionic-radii ratios

A series of conductance measurements of alkali halides NaCl, NaBr, and NaI was performed in a range of 600-1100 K including liquid and solid states for both cooling and heating regimes. The hysteresis phenomenon is observed to be more pronounced for salts with higher ionic-radii ratio (200 K for NaI) with relaxation time exceeding hundreds of hours. At the cooling regime the conductivity drops slowly from a high value typical for liquids at the freezing point to a solid-salt value defined by a Na+ migration energy at the end of the hysteresis interval instead of an abrupt jump expected at the usual first-order transition. A sort of glassification is assumed to be present at the solidification interval of the salts with high ionic-radii ratios.