Thermophysics of the lanthanide hydroxides I. Heat capacities of La(OH)3, Gd(OH)3, and Eu(OH)3 from near 5 to 350 K. Lattice and Schottky contributions

Abstract

From values of the heat capacity of microcrystalline La(OH)3, Gd(OH)3, and Eu(OH)3 determined by precise adiabatic calorimetry from near 10 to 350 K, the Schottky contribution associated with the low-lying J-manifolds of Eu(OH)3 was resolved with the aid of a new lattice-heat-capacity approximation based upon volumetric interpolation between the lattice heat capacities of the La(OH)3 and Gd(OH)3 homologs. This calorimetrically deduced Schottky contribution to the heat capacity of Eu(OH)3 was compared with the same contribution calculated from spectral data. Excellent accord was observed over the entire temperature range investigated. The experimental heat capacities of this study together with previously published low-temperature (0.45 to 18 K) magnetic and heat-capacity data for Gd(OH)3 permit evaluation of thermophysical functions relative to T = 0 for each compound.