Thermophysical properties of the lanthanide sesquisulfides. II. Schottky contributions and magnetic and electronic properties of γ-phase Pr2S3, Tb2S3, and Dy2S3

Abstract

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.

Optical spectra and thermal Schottky levels in dysprosium sesquisulfide

“…Both the experimental and calculated crystal-field splitting of the ground-state multiplet manifold of Dy 3ϩ ( 6 H 15/2 ) are compared with Schottky levels obtained from a recent reassessment of the heat capacity data of ␥-phase Dy 2 S 3 measured by both the Taher and Westrum groups. 17,19 Our analysis of the temperature-dependent ͑hot-band͒ absorption spectra, confirmed by the crystal-field splitting calculations, is able to verify seven of the eight expected twofold degenerate Schottky levels. The eighth level likely corresponds to the highest-energy Stark level in the 6 H 15/2 manifold that cannot be identified with any certainty from the optical data.…”

“…[15][16][17] One of the most complete studies was carried out by Westrum and his co-workers. [18][19][20] Their interpretations were strengthened when analyses of optical and magnetic data were also available to support the Schottky level assignments deduced from analyses of the heat capacity data. [21][22][23] The success of these comparative studies depended on making measurements on samples of similar composition.…”

“…Calorimetric measurements made by Westrum and his group between 5 and 350 K on samples of similar composition could not be reconciled to this explanation. 19 Based on entropy considerations, they proposed that the anomaly was likely due to magnetic ordering. Paramagnetic susceptibility data obtained from the Westrum samples between 2 and 350 K indicated that antiferromagnetic ordering takes place around 3.4 K. 24 However, establishing the low-energy Schottky levels is complicated by the residue of magnetic ordering that contributes to the overall heat capacity observed above 5 K in the Dy 2 S 3 samples.…”

“…Moreover, the optical spectra reported by Taher et al 17 was obtained at temperatures too low to verify the Schottky-level assignments reported by the Westrum group. 19 To resolve these differences, and to establish an independent experimental basis for establishing the Schottky levels, we report a detailed crystal-field splitting analysis of the Dy 3ϩ ion-energy levels in ␥-phase Dy 2 S 3 , having the same composition as the samples used in measuring the heat capacity data. Sixty-two experimental energy ͑Stark͒ levels identified from the optical spectra of various multiplet manifolds, 2Sϩ1 L J , of Dy 3ϩ (4 f 9 ) are compared with a calculated crystal-field splitting, whose initial crystal-field parameters, B nm , were determined from lattice-sum calculations.…”

Investigation on thermophysical properties of RE6UO12(s) (RE=La, Pr, Nd, Sm)

“…The accuracy in various energy levels can be verified from the measured and calculated Schottky heat capacity. This type of correlation of heat capacity with spectroscopy data is largely studied for compounds like RE2O3 [33][34][35][36][37][38][39][40][41], RE2S3 [42][43][44][45][46][47], RE (OH)3 [48][49][50][51][52] and REPO4 [53][54][55][56][57][58][59][60][61][62][63][64]. …”