No abstract

Heat capacity measurements off our lanthanide sesquisulfides La 2 S 3 , Ce 2 S 3 , Nd z S 3 , and Gd z S 3 , prepared in the r phase, have been obtained between 6 and 350 K by adiabatic calorimetry.The total heat capacity has been resolved into lattice, electronic, magnetic, and Schottky components. The Schottky contributions agree well with the calculated values based on the observed s~litting of the ground-state manifold of the rare earth ions occupying sites of S4 symmetry In the Th 3 P 4 structure. The observed splitting is obtained from an analysis of the hot bands in the absorption spectrum and from direct observation of the Stark levels in the far infrared. The Stark levels (all doublets) for Ce 2 S 3 eF s /2) are 0,185, and 358 cm-I ; for Nd z S 3 (4/ 9 / 2 ), they are 0, 76, 150, 180, and 385 cm -I. For La Z S 3 , which has no Schottky or magnetic contributions to the heat capacity, the thermal data can be extrapolated to ° K. The entropy for La 2 S 3 at 298.15 K (as SOIR) is 19.51. Schottky and magnetic ordering at lower temperatures in Ce Z S 3 , Nd 2 S 3 , and Gd 2 S 3 preclude such extrapolation techniques. Therefore the entropy at 298.15 K for these compounds {SO-S°(7 K)}IR, is 21. 34, 22.38, and 20.05, respectively.

Heat-capacity measurements by adiabatic equilibrium calorimetry are reported for γ-phase Pr2S3, Tb2S3, and Dy2S3 between 5 and 350 K. Highly purified samples were prepared and their composition verified by chemical analysis. Precision lattice parameters were determined for each compound and are compared with literature values. The total heat capacity has been resolved into lattice, magnetic, and Schottky components by a volumetric approach. The experimental Schottky contributions accord with the calculated curves based on the crystal-field splitting of the 2S+1LJ ground state of the lanthanide ions occupying sites of S4 symmetry in the Th3P4 lattice. The individual crystal-field electronic energy levels have been obtained in part from an analysis of the hot-band data observed in the absorption spectra of Pr2S3, Tb2S3, and Dy2S3, and from a calculated splitting in which the crystal-field parameters Bkm, were determined from a lattice-sum calculation. Molar thermodynamic properties are reported for all three compounds. The entropy at 298.15 K {S0−S0 (7 K)}, is 22.78R, 22.93R, and 23.36R, for γ-phase Pr2S3, Tb2S3, and Dy2S3, respectively.