Low-temperature specific heat of layered compounds

Specific heat measurements in the temperature range from 1 to 10 K and in magnetic fields up to 1.2 T have been made on a number of layered transition metal dichalcogenide crystal complexes. The thermodynamic critical fieldH _c and the Ginzburg-Landau coherence length and penetration depth have been calculated. For TaS₂ (pyridine)_1/2 and TaS_1.6Se_0.4 (pyridine)_1/2, the coherence length perpendicular to the layers is slightly less than the interlayer separation.Research at Stanford supported by Air Force Office of Scientific Research, Air Force Systems Command, USAF, under grant AFOSR 73-2435B.     

Low-temperature specific heat of Ti-Hf alloys

The effect of alloying on the specific heat of Ti-Hf alloys has been investigated in the temperature range 1.2–4.5 K. A maximum is observed in the electronic specific heat coefficient γ around 35 at % Ti and the Debye temperature θ _D decreases from titanium to hafnium. No superconductivity is found down to the lowest temperature studied.     

Rigid band behavior of platinum-Vanadium alloys: Low-temperature specific heat

Measurements are reported of the specific heat of a number of PtV alloys. The results can be analyzed by using a simple rigid band model. The band shape of platinum is deduced and the number of holes in the platinum d band is estimated to be 0.35, which agrees very well with other determinations. Deviations from the simple rigid band behavior were observed for higher vanadium concentrations and are believed to be caused by interactions between impurity atoms. Using the critical concentration of 6 at %V for interactions to start, the interaction range is estimated.     

Low-temperature specific heat anomalies in the group V transition metals

Anomalies previously reported in the specific heat curve of normal-state niobium at 3 and 9.5 K prompted new measurements on single crystals of niobium, tantalum, and vanadium from their superconductingT _c 's up to 20 K. The upper anomaly was confirmed in Nb and found to occur at 10.3 K. At this temperature theC/T vs. T ² curve changed abruptly from a line with constants ₂ =7.67 mJ/K ² mole and ₂ =241 K to one with ₃ =9.16 mJ/K ² mole and ₃ =250 K. The NbT _c was 9.275 K. Anomalies similar to that occurring at 3 K in the niobium curve were discovered to exist in tantalum and vanadium as well, but at the higher temperatures of 7.19 and 7.47 K, respectively. The tantalum data yielded line constants of ₁ =5.42 mJ/K mole, ₁ =238 K, ₂ =4.36 mJ/K ² mole, and ₂ =228 K and aT _c of 4.475 K. For vanadium ₁ =397 K is higher than previous specific heat values of ₁ =382 K, and in agreement with that obtained from elastic constant measurements (399 K). The discontinuities in the slopes of the specific heat curves are analyzed in terms of anomalies in the electron and phonon spectra of the materials investigated.     

Low-temperature specific heat of beryllium compounds of the first transition-metal series

The low-temperature specific heat of beryllium compounds (Cr-Mn)Be ₂ , (Mn-Fe)Be ₂ , and (Fe _0.95 T _0.05 )Be ₂ , where T represents Cr, Mn, Co, or Ni, was measured between 1.2 and 4.2 K. The variation of the electronic specific heat coefficient as a function of the transition-metal electron/atom ratio is analyzed. There is an increase of for 6<e/a<7, a peak enhanced by clustering effects fore/a 7.15 due to the appearance of ferromagnetism, and a minimum fore/a=8 for the transition from weak to strong ferromagnetism.This paper has been presented at the Second International Conference on Calorimetry and Thermodynamics at Orono, U.S.A., July 1971.Work supported by the Direction des Recherches et Moyens d'Essais, Laboratoire Pierre Weiss, Convention no. 70.34.204.00.480.75.01.     

Low-temperature specific heat of a semiconductor in a strong magnetic field

We calculate the electronic specific heat of a semiconductor (GaAs) at very low temperatures when subjected to a magnetic field strong enough to make the electron distribution nondegenerate. The transition to nondegeneracy is characterized by a large and rapid increase in the specific heat. For large fields the value approaches that of a one-dimensional nondegenerate gas, after first exceeding this value. Zeeman splitting, even with a very smallg factor (0.32), almost doubles the maximum in the specific heat as a function of field.On leave from Centre de Recherches sur les Très Basses Températures, Grenoble, France.     

Ferromagnetic and antiferromagnetic ordering in platinum-manganese alloys: Low-temperature specific heat

Measurements are reported of the specific heat of a number ofPtMn alloys. Interaction between the manganese impurities gives rise to antiferromagnetic or ferromagnetic ordering depending on the impurity concentration, the critical concentration for ferromagnetism being 0.8 at % Mn. Using the effect on the specific heat anomaly of the statistical fluctuations in the number of the impurities in a given volume, the interaction range of the impurities is estimated and found to agree with the band structure of platinum.     

Low-temperature specific heat,thermal conductivity,and ultrasonic velocity of glassy carbons

We have measured the specific heat (0.1<T < 1 K) and thermal conductivity (0.07 <T<300 K) of two glassy carbons, one pyrolysed at 1000C, the other at 2500 C. The temperature dependence of ultrasonic velocity (0.2–300K) was also measured on the 2500C material. The above properties are remarkably similar to those of amorphous materials, yet it appears that these features arise from origins other than the localized excitations responsible for the low-temperature behavior of amorphous materials.Supported in part by U.S. Energy Research and Development Administration grant EY-76- C-02-1198.     

Low-temperature quadrupole and crystalline field effects in the specific heat of solid D2

Measurements have been made of the specific heat of solid D ₂ with concentrations of para-D ₂ between approximately0.9 and6%. The measurements are an extension of previously reported results to 150 mK and to various para-D ₂ concentrations. An anomalous specific heat is observed below 0.6 K which cannot be accounted for by the nearest-neighbor electric quadruple-quadrupole (EQQ) interactions betweenJ=1 molecules. This anomaly is explained in terms of next- and next-next-nearest-neighbor interactions between pairs and nearest-neighbor interactions between triple configurations ofJ=1 molecules. In addition, estimates are presented of the crystalline field splitting parameter (/k) in solid deuterium with lowJ=1 concentration.This work was partially supported by a grant from the National Science Foundation and by a contract with the Office of Naval Research.     

Low-temperature heat capacity of urea

The heat capacity of urea was measured with an adiabatic calorimeter in the temperature range 15–310 K. The data were extrapolated to 0 K by a model function to derive some standard thermodynamic functions including the enthalpy increments ₀ ^T H, the entropy increments ₀ ^T S, and the Giauque function (= ₀ ^TS – ₀ ^T H/T). A simple model for the reproduction of the experimental heat capacities of urea, based on the Debye and Einstein functions, is described. The Debye characteristic temperature determined in this way was compared with those calculated from properties other than the heat capacity. Any positive evidence of a suggested phase transition in urea around 190 K was not observed in the present heat capacity measurements. Possible existence of a phase with a Gibbs energy lower than that realized in the present investigation is discussed briefly.     

Low-temperature heat capacity of yttrium orthotantalate

The heat capacity of yttrium orthotantalate has been determined as a function of temperature by adiabatic calorimetry in the temperature range 0–340 K. Smoothed heat capacity data have been used to calculate the thermodynamic functions of yttrium orthotantalate.     

Low-temperature heat pipes with vapor injection

Two types of heat pipe with low-pressure injectors are considered. The pipes are intended for operation on any orientation in the gravitational field.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 4, pp. 573–580, October, 1977.     

Low-temperature semiconductor resistance thermometer with heat conductor

A 0.5–100 K GaAs thermometer with a toroidal element and a heat conductor improving the thermal contact and mechanical strength is described. At 4.2 K the reproducibility is 10 mK and the thermal resistance is about 10⁴ KW⁻¹ for P ≈ 10⁻⁶ W.     

Low-temperature heat capacity and thermodynamic properties of InSe

The heat capacity of InSe has been measured at temperatures from 11.14 to 325.26 K using an adiabatic calorimeter. The results differ significantly from earlier data (by ～2.2% at 200 K). The smoothed heat capacity data have been used to evaluate temperature-dependent thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) of indium selenide. Its thermodynamic properties under standard conditions are C _p ⁰ (198.15 K) = 49.43 ± 0.10 J/(K mol), S ⁰(298.15 K) = 82.20 ± 0.16 J/(K mol), H ⁰(298.15 K) ? H⁰(0) = 10.94 ± 0.02 kJ/mol, and Φ⁰(298.15 K) = 45.50 ± 0.09 J/(K mol). The Debye characteristic temperature of InSe evaluated from the heat capacity data is 275 ± 15 K.     

Low-temperature heat capacity and thermodynamic functions of GaTe

The heat capacity of GaTe is measured from 6.8 to 337.95 K using adiabatic calorimetry. The results are used to calculate the heat capacity, entropy, enthalpy increment, and reduced Gibbs energy of GaTe in the temperature range 10–320 K under standard conditions. The 298.15-K thermodynamic properties of GaTe are C _p ⁰ (298.15 K) = 48.96 ± 0.10 J/(K mol), S ⁰(298.15 K) = 81.30 ± 0.16 J/(K mol), H ⁰(298.15 K) ? H ⁰(0 K) = 10.84 ± 0.02 kJ/mol, and Φ⁰(298.15 K) = 44.95 ± 0.09 J/(K mol).     

Low-temperature heat capacity and thermodynamic functions of DyVO4

The heat capacity of dysprosium orthovanadate has been determined by adiabatic calorimetry in the range 6.12–343.26 K. The present and earlier data have been used to calculate the thermodynamic functions of DyVO₄ in the temperature range 0–350 K. We have determined the absolute entropy and Gibbs energy of formation of dysprosium orthovanadate: S ⁰(298.15 K) = 148.34 ± 0.11 J/(mol K), Δ_f G ⁰(298.15 K) = ?1671.6 ± 2.1 kJ/mol. An anomaly has been detected at temperatures below 42 K, due to the Jahn-Teller phase transformation (T _C = 14.42 K). We have determined the thermodynamic characteristics of the transformations in the temperature range 0–42.63 K.