Thermophysical properties of the lanthanide sesquisulfides. I. Schottky functions and magnetic and electronic properties of γ‐La2S3, γ‐Ce2S3, γ‐Nd2S3, and γ‐Gd2S3

Abstract

Heat capacity measurements of four lanthanide sesquisulfides La2S3, Ce2S3, Nd2S3, and Gd2S3, prepared in the γ 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 splitting of the ground‐state manifold of the rare earth ions occupying sites of S4 symmetry in the Th3P4 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 Ce2S3 (2F5/2) are 0, 185, and 358 cm−1; for Nd2S3(4I9/2), they are 0, 76, 150, 180, and 385 cm−1. For La2S3, which has no Schottky or magnetic contributions to the heat capacity, the thermal data can be extrapolated to 0 K. The entropy for La2S3 at 298.15 K (as S0/R) is 19.51. Schottky and magnetic ordering at lower temperatures in Ce2S3, Nd2S3, and Gd2S3 preclude such extrapolation techniques. Therefore the entropy at 298.15 K for these compounds {S0–S0(7 K)}/R, is 21.34, 22.38, and 20.05, respectively.