Thermodynamics of the lanthanide halides I. Heat capacities and Schottky anomalies of LaCl3, PrCl3, and NdCl3 from 5 to 350 K

Abstract

The heat capacities of LaCl3, PrCl3, and NdCl3 have been measured from 5 to 350 K by adiabatic calorimetry. No co-operative thermal anomalies were seen in the temperature range investigated but substantial magnetic heat-capacity contributions of the non-cooperative (Schottky) type were found. Subtraction of the heat capacity of the diamagnetic and isostructural LaCl3 from those of the paramagnetic members yields experimental Schottky heat-capacity contributions which are compared with heat capacities derived from spectroscopically determined energy levels. Small discrepancies between the calculated and experimental contributions are probably due to differences in lattice heat capacities between LaCl3 and the others. The values of {(So(298.15 K) - So(0)}/calth K-1 mol-1 are for LaCl3 and NdCl3, 32.88 and 36.67. Due to the possibility of a low-temperature phase transition, the entropy of PrCl3 covers only the experimental range of this research and that of Colwell, Mangum, and Utton. {So(298.15 K) - So(0.294 K)} for PrCl3 is 36.64 calth K-1 mol-1.