Low temperature specific heat of intercalation compounds M x TiS2 (M = 3d transition metals)

Specific heats of intercalation compounds Fe_x TiS₂ (x = 0–1/3) and M_1/4 TiS₂ (M = Mn, Fe, Co and Ni) have been measured in the temperature range 0.35–5 K using an ac calorimetry method. The temperature dependence of the specific heats for these materials is written as the sum of electronic, lattice and anomalous terms. The anomalous specific heats show a Schottky type behavior, which is due to a very small amount of localized 3d atoms with crystal-field splittings, but the remaining majority of the intercalated guest 3d atoms are regarded as having itinerant electron character that contributes to the enhancement of the density of states at the Fermi energy or of electronic specific heat coefficient.     

Thermal Expansion and Isothermal Compressibility of TlGaS2

The thermal expansion and isothermal compressibility of TlGaS₂ were measured between 77 K and room temperature. No anomalies in the temperature dependences of these properties were detected. The experimental data were used to evaluate the Debye temperature, rms dynamic atomic displacements, the difference between the specific heats at constant pressure and constant volume (C _p – C _V), and the Grüneisen parameter. The appreciable discrepancy between the C _p – C _V values calculated using thermodynamic relations and an empirical formula is attributed to the pronounced anisotropy of TlGaS₂.     

Constant-volume specific heat of solid argon

Specific heats of solid argon were measured between 25 K and 120 K in a closed pressure vessel. Between 60 K and the melting point of 120 K the solid filled the vessel, and at the m.p. the pressure was 1.6 kbar. After correction for the nonrigidity of the container, we find thatC _v increases by 7.3% between 60 K and 120 K, reaching 2.8 R. Comparison with recent calculations based on self-consistent phonon theory reveals substantial discrepancies from the data, indicating the necessity of including higher-order terms in the theory.Research supported by the National Science Foundation and the Rutgers University Research Council.     

Anisotropic gap distortion due to superflow and the depairing critical current in superfluid 3He-B

The specific heats of UAs and the isostructural nonmagnetic homolog ThAs have been measured in the temperature range 5–300 K. While the latter compound displays a regular smooth curve C _p (T), UAs shows two sharp anomalies. The first anomaly, around 64 K, may be ascribed to the magnetic transition from type IA to type I antiferromagnetic structure; the second anomaly, at 122.8 K, corresponds to the Néel temperature. An analysis of the experimental curve C _p (T) for UAs has been carried out by several different methods to get the magnetic contribution to the specific heat with the best possible accuracy. The resulting magnetic entropy depends on the method and its maximum value at 250 K is 0.8 R ln 4, assuming a high-temperature value of the electronic heat capacity coefficient – 33 mJ/K² mole. No anomaly at 41 K was observed whatever thermal treatment was used to prepare the UAs samples.     

Molecular-dynamics simulation of the high-pressure properties of rubidium

An embedded-atom potential for rubidium has been calculated with the parameters chosen with the use of the results of the static tests at a temperature of 300 K and pressures up to 45 GPa, as well as the results of the shock tests at pressures up to 39 GPa. The molecular-dynamics simulation has been performed for temperatures of 300–10 000 K and pressures up to ∼94 GPa. The potential determined from the shock-test data does not provide complete agreement with the static data for 300 K. The pressure, energy, and specific heats C _V and C _p have been calculated for the compression up to 20% of the normal pressure and for temperatures up to 10 000 K. The derivative (∂p/∂T) _V is positive for all of the molar-volume and temperature values except for a compression ratio of 30%. Compression up to a factor of 2.5 or more is accompanied by the partial amorphization of the models, which is enhanced with heating. The calculations of the temperature along the Hugoniot curve under the assumption that the Grüneisen parameter and adiabatic compression modulus are independent of the temperature provide an incorrect molar-volume dependence of the pressure at 0 K.     

Heat capacity studies of ThP and UP0.5As0.5 solid solution. Reanalyzing UP data

The specific heats of ThP and the solid solution UP_0.5As_0.5 have been measured in the temperature range 5–300 K. While ThP has a regularC _p (T) behavior, the mixed compound exhibits several low-temperature anomalies. An analysis of the experimental data for UP_0.5As_0.5 and reanalysis of previously published heat capacity results for UP have been performed. The temperature dependence of the magnetic entropy, which at 300 K reaches a value close toR ln 4 for both species, confirms the U³⁺ state for uranium atoms in these compounds. The value of the electronic heat capacity coefficient _p in the paramagnetic state has also been extracted from the experimental data. It is far smaller than the respective low-temperature value (0).     

Structural transformation-induced magnetic ordering in degenerate magnetic semiconductors

Electrical properties and molar specific heats have been measured in the temperature range 2–300 K of Bridgman-grown Sn_1–x Cr _x Te crystals. In addition to the paramagnetic-to-ferro or ferrimagnetic transition temperatureT _c (= 150–300 K), in this magnetic system there is another characteristic temperatureT _AHE (= 4–5 K), above which the anomalous Hall effects vanish and around which the specific heats show a small peak, indicating an extra magnetic transition. The low-temperature transition is considered as induced by a cubic-to-rhombohedral structural phase transition of the host SnTe crystal occurring at a critical temperature ofT _s (= 80–100 K). Data on the isothermal annealing of these crystals are also presented.     

Low temperature heat capacity measurements on HoBa2Cu3O7−δ

Specific heats were measured on two samples of HoBa₂Cu₃O_7−δ in the temperature range 1·7 K to 10 K. In addition to the known Schottky behaviour, a peak in the specific heat curve was observed near 7·9 K in both the samples. This peak is probably due to impurity contribution and the specific heat measurements were undertaken in holmium oxide (Ho₂O₃), which was the suspected impurity. However, no peak was observed in the specific heat curve of holmium oxide     

Effect of magnetic field on the specific heats of intercalation compounds Mx TiS2 (M=3d transition metals)

Specific heats of single crystals of intercalation compounds M_xTiS₂ (M=Mn, Fe, Co, and Ni) have been measured using ac calorimetric method over the temperature range T = 0.38–14 K under magnetic fields up to 4.5 T. Considering the lattice dynamical properties of these intercalates, we have analyzed the observed specific heat data C, which can be expressed by the sum of electronic, lattice, magnetic, and anomalous terms, C = T + T³ + C_mag + C_a, where C_a is of a Schottky type. The temperature and magnetic field dependences of and C_mag are discussed from various viewpoints, such as existing spin fluctuation model, which reveals that the itinerant electron picture is appropriate to understand the electronic and magnetic properties of this material system.     

Normal-state transport properties of fullerene superconductors

The normal-state transport properties of alkali-metal-doped fullerene crystals are explored. The Hall effect has been measured in K_xC₆₀ from room temperature toT _c . The electrical resistivity for K₃C₆₀ and Rb₃C₆₀ has been measured over a wide temperature range (20–650 K), and notable differences are observed for the materials at both low and high temperatures. The electrical resistivity of Rb₃C₆₀ has been measured in hydrostatic pressures up to 9 kbar. The resistivity is highly pressure sensitive. The transport results give an insight into the normal-state conduction mechanism and thus have consequences for the superconductivity mechanism.     

Specific heat studies of lanthanum and yttrium sesquicarbides

The specific heats of the sesquicarbides LaC_1.35 and La_0.9Th_0.1C_1.6 (prepared by arc melting) and YC_1.35 (prepared by a high-pressure technique) have been measured for the first time. No bulk specific heat anomaly appears in either lanthanum compound, even though (1) inductively measured super-conducting transition temperatures are respectively high (11.0 K for LaC_1.35 and 12.7 K for La_0.9Th_0.1C_1.6) and (2) YC_1.35 is a bulk superconductor with aT _c =10.5 K and Y_0.7Th_0.3C_1.58 (also prepared by high pressure) was previously reported to be a bulk superconductor with aT _c =17.1 K. The apparent correlation with preparation technique is discussed.Work performed under the auspices of the Department of Energy.     

Volumetric measurements under pressure for 2,2,4-trimethylpentane at temperatures up to 353.15 K and for benzene and three of their mixtures at temperatures up to 348.15 K

(p, V, T) data have been obtained in the form of volume ratios relative to 0.1 MPa for benzene (298.15 to 348.15 K), 2,2,4-trimethylpentane (TMP) (313.15 to 353.15 K), and their mixtures near 0.25, 0.5, and 0.75 mole fraction of benzene (313.15 to 348.15 K) for pressures up to near the freezing pressures for benzene and the mixtures, and up to 400 MPa for TMP. Isothermal compressibilitiesκ _T, isobaric expansivitie α, changes in heat capacity at constant pressureΔC _p, and excess molar volumesV ^E have been determined from the data. Literature data at atmospheric pressure have been used to convert theΔC _p toC _p at several temperatures. The isobars for α over the temperature range 278.15 to 353.15 K for TMP intersect near 47 MPa and reverse their order in temperature when plotted against pressure; normalization of the α's by dividing the values at each temperature by the α at 0.1 MPa prevents both the intersection and the reversal of the order. TheV ^E are positive and have an unusual dependence on pressure: they increase with temperature and pressure so that the order of the curves for 0.1, 50, and 100 MPa changes in going from 313.15 to 348.15 K.     

Constant-volume specific heat of solid xenon

Specific heats of solid xenon were measured between 110 and 223 K in a closed pressure vessel. In this temperature interval the pressure increased from the vapor pressure of the solid at 110 K to about 1.7 kbar at the melting point. After a small correction for the nonrigidity of the container, we find that c_v increases from 2.9R at 110 K to the classical Dulong-Petit value of 3R at 200 K. The behavior of the specific heat in the vicinity of the melting point depended on the treatment of the samples.Research supported by the National Science Foundation. This paper is based on a thesis submitted to the Graduate Faculty of Rutgers University in partial fulfillment of the requirements for the PhD degree.     

Thermodynamic properties by levitation calorimetry — V. High-temperature heat content of liquid gallium

The heat content (enthalpy) of liquid gallium relative to the supercooled liquid state at 298.15 K has been measured by levitation calorimetry over the temperature range 1412–1630 K. Thermal energy increments were determined using an aluminum block calorimeter of conventional design. The sharp decrease of C _p with increasing temperature observed just above the melting point does not persist up to the high temperatures of the present work. When combined with recent laser-flash calorimetry results from the literature, the present work indicates that C _p is 26.46 ± 0.71 J · g-atom^–1 · K^–1 over the temperature range 587–1630 K.Paper presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.     

The specific heat of copper at temperatures below 0.2 K

The specific heat of high-purity copper has been measured over the temperature range of 0.03–0.2 K. It is shown that an anomaly appears in the specific heats of some samples. The temperature dependence is ~T ^\s-2 at T \> 0.03 K, and at 0.03 K the magnitude is equal to that of the contribution from conduction electrons. We have not been able to explain the origin of this anomaly.This work was supported in part by the U.S. Department of Energy under contract DE-AC02-76ER01198.     

Thermal Property Measurements and Enthalpy Calculation of the Lithium Bromide+Lithium Iodide+1,3-Propanediol+Water System

The lithium bromide+lithium iodide+1,3-propanediol+water [LiBr/LiI mole ratio=4 and (LiBr+LiI)/HO(CH₂)₃ OH mass ratio=4] solution is being considered as a potential working fluid for an absorption chiller. Heat capacities at four temperatures, 283.15, 298.15, 313.15, and 333.15 K, were measured in the range from 50 to 70 mass%. In addition, the differential heats of dilution at 298.15 K were measured in the range from 45.3 to 71.8 mass%. Each individual data set was correlated with a proper regression equation with a high accuracy. A new enthalpy calculation method for the working fluids containing organics was proposed. The calculation method correlated the heat capacity (at various temperatures and concentrations) and the differential heat of dilution (at ambient temperature and various concentrations). The present method was applied for the construction of enthalpy–concentration (H–T–X) diagrams with high confidence.     

Heat capacity and thermodynamic functions of LaVO<Subscript>4</Subscript> and LuVO<Subscript>4</Subscript> from 7 to 345 K

The heat capacities of lanthanum and lutetium orthovanadates have been measured at temperatures from 7 to 345 K using an adiabatic calorimeter. No anomalies have been detected in the heat capacity data. The thermodynamic functions (C _p ⁰(T), S ⁰(T), and H ⁰(T) − H ⁰(0)) of the two compounds have been calculated in the temperature range studied, and their Debye characteristic temperatures have been estimated.     

Specific heats of solid hydrogen,solid deuterium,and solid mixtures of hydrogen and deuterium

Measurements have been made in the temperature range 0.5–5 K of the specific heats of pure solid H₂, pure solid D₂, and four solid mixtures of H₂ and D₂ with D₂ fractions between 15 and 95%, all of which systems had low concentrationc of molecules in the rotational stateJ=1. For the H₂,c=0.0023, and for the D₂,c=0.030. It was found that the observed specific heats could be described as the sum of three terms as follows. (1) A lattice specific heat. This was found to follow aT ³ function with _D =122 K for solid H₂ and _D=113.8 K for solid D₂. For the solid mixtures the lattice specifi heats have in first approximation values given by a weighted mean of the lattice specific heats of the pure components. (2) A Schottky term with a maximum at about 1.3 K for solid H₂ and 1.4 K for solid D₂, which can quantitatively be described in terms of electric quadrupole-quadrupole (EQQ) interactions in nearest-neighbor pairs and triples of molecules in the rotational stateJ=1. This term led to evaluation of , the EQQ interaction energy, giving /k=0.9 ± 0.1 K for solid H₂ and 0.93 ± 0.05 K for solid D₂. It was found, moreover, that in solid H₂ there was an appreciable enhancement with time of the number of clusters of molecules in the rotational stateJ=1 at the expense of the number of isolated singles of similar molecules, due to rotation diffusion. On the other hand no rotation diffusion was observed in solid D₂ or in the solid mixtures of H₂ and D₂, except possibly in those mixtures containing 85% H₂. (3) A second anomalous term occurring at temperatures below about 0.8 K and, by extrapolation, having its maximum below 0.5 K (the lowest temperature of our measurements). This anomaly was observed only in those samples containing D₂ and is, as yet, unexplained in detail. A further major conclusion from our results in the temperature range 0.5–5 K is that there was no evidence in the form of a sharp anomalous jump in the specific heat of any of the mixtures which could be interpreted as indicating the occurrence of isotopic phase separation. This absence of phase separation is noted, in spite of the fact that thermodynamically it is energetically favorable in the temperature range of observation.Work partially supported by a grant from the National Science Foundation and by contracts with the Office of Naval Research and DOD (Themis Program).     

Equation of State for <Emphasis Type="Italic">C</Emphasis><Subscript>60</Subscript> Fullerene Aqueous Solutions

In the present work PVT data of the C₆₀ fullerene aqueous solution (C₆₀ FAS) were measured as a function of the concentration of C₆₀ molecules using the variable cell method with metal bellows in the temperature range from 295 to 360 K at pressures from 0.1 to 103.2 MPa. On the liquid–vapor equilibrium line the density (ρ) of the C₆₀ FAS was measured using the pycnometer method. As a result, numerical values for the isothermal modulus of elasticity (K_T), isobaric expansivity (α_P), isothermal deviation of entropy factor (TΔS), enthalpy (ΔH), and internal energy (ΔU) have been determined. Finally, an equation of state for the C₆₀FAS was obtained for the first time.     

Low-temperature adsorption isotherms of 3He and para-H2 on grafoil and their normalization

Measurements have been made of the adsorption isotherms of ³He and of para-hydrogen (p-H₂), on bare Grafoil, the former in the temperature range 0.88–1.23 K, and the latter in the temperature range 10.0–20.0 K. For p-H₂ the quantity of material adsorbed plotted against (p/p ₀) ^T yields a single temperature-independent curve, as would follow from the potential theory for multilayer adsorption, and as emphasized by Chester et al. in 1974. The same behavior was found for ³He on Grafoil, except that deviations from a single temperature-independent curve occurred at the higher temperatures. For p-H₂ on Grafoil it is to be noted that the isotherms taken below the triple point of free, bulk p-H₂ fit the same single temperature-independent curve as do the isotherms measured at temperatures between the triple point and the boiling point. From the data, the isosteric heats of adsorption were calculated over a wide range of coverage and this provided further experimental evidence for the similarity between the uppermost layers of thick adsorbed films and the free liquid of the same substance.Supported by the National Science Foundation and the Brazilian National Council of Scientific and Technological Development (CNPq).