Thermophysical properties of the lanthanide sesquisulfides. III. Determination of Schottky and lattice heat-capacity contributions of γ-phase Sm2S3 and evaluation of the thermophysical properties of the γ-phase Ln2S3 subset

Abstract

We report the experimental heat capacity of γ-phase Sm2S3 and derived thermophysical properties at selected temperatures. The entropy, enthalpy increments, and Gibbs energy function are 21.50R, 3063R⋅K, and 11.23R at 298.15 K. The experimental heat capacity is made up of lattice and electronic (Schottky) contributions. The lattice contribution is determined for all γ-phase lanthanide sesquisulfides (Ln2S3 ) using the Komada/Westrum model. The difference between the experimental heat capacity and the deduced lattice heat capacity is analyzed as the Schottky contribution. Comparisons are made between the calorimetric Schottky contributions and those determined based on crystal-field electronic energy levels of Ln3+ ions in the lattice and between the Schottky contributions obtained from the empirical volumetric priority approach and from the Komada/Westrum theoretical approach. Predictions for the thermophysical properties of γ-phase Eu2S3 and γ-phase Pm2S3 (unavailable for experimental determination) are also presented.