John B. Gruber

Low-temperature heat capacities, thermophysical properties, optical spectra, and analysis of Schottky contributions to Pr(OH)3☆

From values of the heat capacity of microcrystalline Pr(OH)3 determined by precise adiabatic calorimetry from 15 to 350 K, the Schottky contribution associated with all but the lowest Stark level was resolved with the aid of a model of the lattice heat capacity based upon the molar volumes of the lanthanide trihydroxides. Visible and infrared absorption spectra were taken at approximately 95 K on microcrystalline mulls and the energy-level scheme and crystalline electric-field parameters evaluated. The Schottky contribution of all levels above the first excited state (μ = 3) was resolved by a new scheme for modeling the lattice contribution and compared with the same contribution deduced from the spectral results. Excellent accord was observed. These results together with magnetic results and the first excited Stark level were used to adjust the low-temperature heat capacities and thermodynamic functions so as to evaluate CpR, SoR, and − {Go − Ho(0)}RT, at 298.15 K as 14.154, 15.84, and 7.766, respectively.

Absorption spectrum, energy levels, and crystal‐field parameters of Tm3+:LaCl3

Optical absorption spectra and energy levels of Tm3+ in LaCl3 are reported. A crystal‐field Hamiltonian of C3h symmetry is used to fit the data; a best fit rms deviation of 3.0 cm−1 is obtained between 27 experimental and theoretical energy levels with the following crystal field parameters: B20=226.9, B40=−241.0, B60=−423.6, and B66=256.3 (all in cm−1). Results obtained here for Tm3+ are compared with results on other lanthanides in LaCl3. Point–charge and dipole lattice sums are performed and compared with phenomenological crystal‐field components obtained from Bnm of various lanthanides in LaCl3.

Polarized absorption spectra and energy levels for U3+(5f3) in LaCl3

Polarized absorption spectra covering the wavelength range 5600 to 25 000 A are reported for U3+(5f 3) doped into single crystal LaCl3. Spectra were recorded at liquid helium, liquid nitrogen, and at room temperatures. Temperature‐dependent polarized spectra help establish many crystalline electric‐field (CEF) split J levels not directly excited from the ground state due to selection rules for C3h symmetry. Analysis of the data confirms the earlier (1959) assignments made by S. P. Cook at The Johns Hopkins University to the ground state manifold Stark levels. For 4I9/2, the ground state manifold, we find: μ (±5/2) =0, μ (±1/2) =210, μ (±3/2) =241, μ (±5/2) =440, and μ (±3/2) =458 all in energy units of cm−1. Uncertainty in establishing these levels is within several wave numbers and involves over 150 temperature‐dependent transitions.

Average magnetic susceptibility of rare earth sesquisulfides

Abstract Measurements of the average magnetic susceptibility of Nd 2 S 3 , Gd 2 S 3 and Dy 2 S 3 are reported over the temperature range 4–300 K. Paramagnetic Gd 2 S 3 becomes ferromagnetic below about 30 K. Magnetic ordering in Nd 2 S 3 appears to take place near 60 K. Dy 2 S 3 appears to remain paramagnetic to the lowest temperatures investigated. Reasonable agreement has been obtained between a calculation using Van Vlecks theory and the data obtained from these Faraday experiments.

Electrical Resistivity of (NdxGd1−x)3−yS4: Magnetic Effects

We wish to report the electrical resistivity p of single crystal (NdxGd1−x)3−yS4 where (0 ≤ × ≤ 1, 0 < y < 0. 33) between 2 and 300 K. X-ray diffraction analyses reveal that all samples possess the high temperature γ-phase structure which is represented as the bcc Th3P4 defect structure. The electrical resistivity was measured by a four point DC-technique with pressure contacts at the gold-coated bars of samples with dimensions of 1 × 2 × 8 mm. The measured resistivity values without and with a magnetic field of 7. 7 kG as a function of 1/T are shown in Fig. 1. As shown in the figure, the resistivity in each sample decreases linearly with decreasing temperature and goes through a minimum as the Curie temperature is reached. The variations in ρmin. and temperatures of ρmin. are attributed to different rare earth concentrations as well as the total metal to sulfur ratios in the samples. Application of a magnetic field reduces the resistivity below about 60 K in all samples. The ρ vs T curves for all samples strongly suggest that the increase in resistivity is directly related to the state of magnetic ordering through temperature or applied magnetic field. Since the carrier concentration is greater than 8 × 1019/cm3 in all samples, the model of Cutler and Mott (1) suggests that EF(Fermi energy) lies near but above Ec (conduction band energy).

Thermophysics of the Lanthanide Trichlorides—Reanalysis of the Schottky Heat Capacity Contributions

The heat capacity data on the anhydrous lanthanide trichlorides from 5 to 350 K of Sommers and Westrum provide an excellent opportunity to further test the volumetric lattice heat-capacity approximation method. Schottky contributions in PrCl3, SmCl3, and EuCl3 were calorimetrically derived using the volume-weighted interpolation between the lattice heat capacities of the La and Gd homologs. Previously qualitative agreement had been observed upon comparison of these calorimetrically derived Schottky contributions with those calculated from spectroscopic data obtained for Ln(III) doped LaCl3 crystals. Excellent accord between “spectroscopic” and “calorimetric” Schottky contributions is achieved by adjusting the Stark-level energies to represent those of the concentrated salts through extrapolation of the Ln(III) doped LaCl3 energies to stronger crystal fields either empirically or by means of estimated crystal-field parameters. These methods are described and the resulting energy levels are compared with the spectroscopic data that do exist for the concentrated trichlorides.

Absorption spectrum of Yb3+(4f13) IN[(C6H5)3PH]3 YbCl6☆

Abstract Optical absorption spectra taken at 300 and 77 K are reported for six-fold octahedrally coordinated Yb 3+ (4f 13 ) in [(C 6 H 5 ) 3 PH] 3 YbCl 6 . In addition to vibronic spectra we observe electronic transitions which suggest that inversion symmetry is lifted by a small distortion similar to that reported for the Nd 3+ (4f 3 ) spectrum of the corresponding salt. The vibronic as well as the electronic transition have been analyzed on the basis of six-fold octahedral symmetry. The analysis appears reasonable and consistent in comparison with other rare-earth ions that have been studied in similar cubic and octahedral environments.

Magnetic and Thermal Properties of Ce3−xS4

The high temperature phase of cerium sesquisulfide is characterized by the Th3P4 bcc defect structure and usually expressed as Ce3−xVxS4 (0 ≤ × ≤ 0. 33) to indicate the vacancies Vx in the rare earth sublattice. (1) Between the extremes of Ce3S4 (x = 0) and Ce2S3 (x = 0. 33) various ratios between Ce and S are possible and when prepared and melted into ingots or single crystals all samples show the same Th3P4 defect structure. (2) This note reports the magnetic susceptibility (X) and the heat capacity (Cp) for two such samples, namely CeS1.39 and CeS1.46.

Abstract: Magnetic and thermal properties of YbS1.387

Magnetic and thermal properties of Ybs1.387 are presented between 4 and 300 K for the magnetic susceptibility of (χ) and between 2 and 20 K for the heat capacity (Cp). The sample appears to be paramagnetic over the temperature range studied. A plausible explanation for both the Cp and the χ data obtained can be made by considering the Yb3+(4f) ions to be found in a crystal line environment where the ground state level 2F7/2 is split by the crystalline electric field into four Kramers doublets found at 0, 6, 120, and 300 cm−1.