Bruce H. Justice

Molecular Freedom of the Ammonium Ion. Heat Capacity and Thermodynamic Properties of Ammonium Perchlorate from 5°–350°K

The heat capacity of NH4ClO4 has been determined by adiabatic calorimetry from 5°–350°K and found to be of simple sigmate character without thermal anomalies. The heat capacity (Cp), entropy (S°), enthalpy function (H°−H°0) / T, and Gibbs energy function (G°−G0°) / T evaluated at 298.15°K from these data are 30.61, 44.02, 20.24, and −23.78 cal/(gfm °K). Combination of these values with aqueous NH4ClO4 thermochemical data suggests the absence of zero‐point entropy. Comparison with the heat capacity of isostructural KClO4 permits resolution of the molecular dynamics of the ammonium ions and leads to the conclusion that these ions are restricted rotators, prevented from freely rotating by comparatively low‐energy barriers.

Optical spectra and thermal Schottky levels in the high temperature γ-phase of the lanthanide sesquisulfides

Abstract The detailed crystal-field splitting of the energy levels of the trivalent lanthanide ions (Ln 3+ ) in the high temperature γ-phase of the lanthanide sesquisulfides (Ln 2 S 3 ) are compared with calculations that employ lattice-sum and three-parameter theory models. The results are also compared with the thermal Schottky levels deduced from heat capacity measurements on samples of Ln 2 S 3 having similar composition and physical properties. Good agreement is reached between the calculated levels and the experimental levels that come from the two independent sources of data. It appears that the Ln 3+ site symmetry (S 4 ) in the Th 3 P 4 defect structure of the high-temperature phase of Ln 2 S 3 can be represented by a slightly higher symmetry (D 2d ) that reflects the symmetry of the Ln 3+ polyhedra in a lattice that has random cation vacancies throughout the unit cell.

Optical spectra and thermal Schottky levels in dysprosium sesquisulfide

We report a detailed crystal-field splitting analysis of the energy levels of Dy3+(4f9) in single crystals of Dy2S3 that have the Th3P4 cubic defect structure. From an analysis of the temperature-dependent absorption spectra, we have identified seven of the eight crystal-field split energy (Stark) levels of the ground-state multiplet manifold, 6H15/2. Sixty-two experimental Stark levels from various multiplet manifolds of Dy3+ are compared with a calculated crystal-field splitting, whose initial crystal-field parameters, Bnm, were determined from lattice-sum calculations. The rms deviation between experimental and calculated levels is 7 cm−1. Both the experimental and calculated crystal-field splitting of the 6H15/2 manifold are compared with an assignment of Schottky levels obtained from a reassessment of heat capacity data reported earlier. Based on entropy considerations and verification of the Schottky level assignments by analyses of the optical and magnetic susceptibility data, we conclude that the ...

Thermophysical properties of CeB6 and PrB6 at subambient temperatures

Equilibrium adiabatic heat-capacity measurements have been made on zone refined samples of CeB6 and PrB6. Companion measurements made on LaB6, NdB6, and GdB6 have been reported elsewhere. These show cooperative lambda-type anomalies associated with antiferro-magnetic ordering. Except for lanthanum hexaboride, Schottky internal crystal field levels result in significant contributions to the thermodynamic functions. The gross thermodynamic properties at 298.15 K heat capacity (Cp/R), entropy increment (ΔT0,mS0/R), and Gibbs energy function are correlated with the nature of the lanthanide. For LaB6, CeB6, PrB6, NdB6, and GdB6 the three properties are, respectively: {11.654, 12.014, 11.997, 11.916, 11.695} Cp/R; {10.001, 11.803, 12.430, 12.558, 13.982} S0/R, and finally {4.379, 5.912, 6.232, 6.451, 7.905}Φ0m/R.