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 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.

Revisiting the thermophysical properties of the A-type hexagonal lanthanide sesquioxides between temperatures of 5 K and 1000 K

“…Corresponding data points were read from the compromise curve between T = 180 K and 298 K, while placing no statistical weight on Lutsareva's points above T = 185 K. (6) These data were combined to yield the final curve shown in figure 2. The thermodynamic functions in table 4 are materially the same as those of Pankratz, (28) but they are referenced to T = 0 K with this analysis.…”

“…Giauque (27) was able to measure both the co-operative transition and the Schottky peak on other salts, using the co-operative transition as the cooling lever in adiabatic demagnetization experiments with the concomitant correlation of the entropy and the temperature scale. Using the volumetric priority method, (28) the lattice heat capacity C p,lat for either Ce 2 O 3 or Pr 2 O 3 is expressed as,…”

“…The resolution of the components of the heat capacity of Nd 2 O 3 with the available data (4,11,14) supports the aforementioned volumetric priority scheme (15) up to temperatures above 1000 K. Thus, the resolution of the components of the heat capacities of Ce 2 O 3 and Pr 2 O 3 is a test of the volumetric lattice interpolation and the lattice-sum calculations of the crystal field spectra. By using lattice-sum models together with the three-parameter theory for trivalent rare earth ions, (17) calculations of the crystal-field splitting of the electronic states (4f n ) determine the Schottky heat capacity.…”

“…In concert with crystal field spectra and concomitant calculations such resolution can be verified. The lattice contribution is obtained from the volumetric priority scheme of Westrum et al (15) described in detail below. In the present study, the lattice heat capacities of La 2 O 3 and Nd 2 O 3 , acting as anchors for the volumetric interpolation, are derived with some accuracy and precision from consistent spectral and thermal data to yield further lattice heat capacities of Ce 2 O 3 and Pr 2 O 3 .…”

The thermal capacity and enthalpy of gadolinium sesquiselenide over a wide temperature range

“…The specimens were made from the elemental components of high purity: Se (OSCh 22- temperatures (a) and high ones (b): curves 2 and 4 have been constructed from the data of [12] and [14], respectively crucibles had previously been annealed at 900-1000 K. The tubes were evacuated to 0.1-0.3 Pa with intermediate fourfold flushing with pure inert gas and were sealed. The heat treatment was conducted in several stages: synthesis at 700-900 K in electrical resistance ovens until selenium had reacted completely with the gadolinium; synthesis at 1400-1450 K for 20-30 h; short-time melting by high-frequency heating; and homogenizing annealing at 1500-1700 K for 3-4 h. Microstructure in XRD analyses show that the selenide was of single-phase structure (structure type Th 3 P 4 )…”