Enthalpies of phase transition in the lanthanide chlorides LaCl 3, CeCl 3, PrCl 3, NdCl 3, GdCl 3, DyCl 3, ErCl 3 and TmCl 3

Abstract

The enthalpies of phase transition in the lanthanide chlorides have been measured with a differential scanning calorimeter and also with a Calvet-type microcalorimeter to within an experimental error of ±2%. The molar enthalpies of fusion of LaCl 3, CeCl 3, PrCl 3, NdCl 3, GdCl 3, DyCl 3, ErCl 3 and TmCl 3 are 55.7, 55.5, 52.1, 48.1, 40.6, 22.8, 31.1 and 35.6 kJ mol −1 respectively. The existence of a solid-solid phase transition was found in DyCl 3 and ErCl 3 at 611 and 1025 K with a molar enthalpy of transition of 1.4 and 5.3 kJ mol −1 respectively. A significant difference (8.5 kJ mol −1) between the absolute values of molar enthalpies of crystallization and fusion was found for LaCl 3 at 1124±3 K; this unusual behaviour was explained by an “after-fusion” effect. The entropies of fusion are discussed in terms of structural types of the lanthanide chlorides.