Low-temperature Thermal Properties Research Articles

Low temperature thermal properties of two singlet ground state systems: Pr 3Tl and PrSn 3

Low temperature thermal properties of Pr 3Tl and PrSn 3, probing magnetoelastic interactions, are discussed. Emphasized is their behaviour at the magnetic phase transitions of these compounds.

Low temperature thermal properties and intrinsic defects in vitreous silica

Measurements of the low temperature specific heatC p (0.04K≦T≦2.4K) and thermal conductivityk (0.5K≦T≦20K) of high purity vitreous silica (Suprasil W) in the as-received and electron-irradiated states are reported. In the temperature range where the localized excitations inherent in glasses dominateC p (T≲0.5K) no change is observed upon electron irradiation of up to 1019e− (total dose). An anomalyδC around 1.8K is observed inC p which is reduced by 40% upon irradiation. However, ask is not affected by electron irradiation, localized excitations as origin forδC can be ruled out. The density of paramagnetic centers in the most heavily irradiated sample is 5⋅1017cm−3 as obtained from the ESR signal. It has been suggested that these centers have diamagnetic “precursors” in the unirradiated glass. Our measurements indicate that those defects are not associated with the localized excitations.

Possible existence of bound state Frenkel vacancies in solid 3He

The effects on the low temperature (T ≲ 15 mK) magnetic and thermal properties of solid 3He due to the presence of bound state Frenkel vacancies (BFV) are analyzed. The coupling of a 3He to a BFV contributes to the zero point motion of the 3He. Assuming that the BFV are strongly interacting and propagate coherently through the crystal, we find good qualitative agreement with both the specific heat and magnetic susceptibility data.

Effect of magnetocrystalline anisotropy on the low temperature heat capacity of HoAl2

Rare earth–aluminum compounds of the composition RAl2 crystallize in Laves phase cubic structure. Low temperature magnetic and thermal properties of these compounds have been investigated thoroughly during the past decade. The occurrence of large magnetocrystalline anisotropy results in significant modifications of magnetic and thermal properties of these materials. In the present study the heat capacity of ferromagnetically ordered HoAl2 was measured in the temperature range 1.5–12 K. An examination of the data reveals that the measured heat capacity Cp can be described by the relation Cp=CN(T)+CM(T)+γT+βT3, where CN is the nuclear term, CM the magnetic term; γT and βT3 are electronic and lattice heat capacities, respectively. A detailed analysis of the magnetic heat capacity term indicates a dependence of the form CM=AT3/2 exp(−Δ/kT) with Δ/k=6.0 K. The exponential dependence of CM is strong evidence of the presence of large magnetocrystalline anisotropy in HoAl2.

Low temperature heat capacities and thermal properties of DyAl 2, ErAl 2 and LuAl 2

The heat capacities of the compounds DyAl 2, ErAl 2 and LuAl 2 were measured in an adiabatic calorimeter from approximately 5 to 300 K. The compounds DyAl 2 and ErAl 2 show C P anomalies at 58.0 and 10.2 K, respectively, which are attributed to the destruction of magnetic order. In order to separate the crystal field and magnetic contributions from the measured heat capacities, it was necessary to evaluate the lattice heat capacity. The lattice term, C L was obtained from the C P data of LuAl 2 by a method of interpolation which gave values of C L for an arbitrary R Al 2 compound. Using this “interpolated lattice blank”, excess entropies associated with the crystal field and magnetic terms were computed throughout the series. These values are quite close to R In (2 J + 1). The results also indicate that, for the compounds studied, the degeneracy of the lowest ground state is completely lifted. In addition, the magnetic contribution to the heat capacity of the magnetically ordered R A1 2 phases was found to exhibit an exponential dependence below the temperature corresponding to the spin wave energy gap and a T 3 2 dependence above this temperature. Detailed calculations were performed to characterize the influence of cubic crystal field in ErAl 2 on the 4 I 15 2 ground state multiplet of the Er 3+ ion. It is concluded that the magnetic ordering in ErAl 2 takes place within the Γ 8 3 quartet state. Smoothed values of heat capacity, entropy and related thermodynamic functions are tabulated.

Low temperature heat capacities and thermal properties of DyAl 2, ErAl 2 and LuAl 2

Low temperature heat capacities and thermal properties of DyAl 2, ErAl 2 and LuAl 2

Low temperature specific heat of glasses and amorphous solids

IN a previous paper1 we attributed the anomalous low temperature thermal properties of amorphous materials to the inherent nature of the amorphous state, conceived of as the crystalline state saturated with the most favoured dislocations2. Using Granato's vibrating string model3 of a dislocation, an estimate of the excess specific heat of Pd0.775 Cu0.06 Si0.165 was provided. The purpose of the present note is to clarify several points in our earlier paper.

Mechanical and thermal properties of filamentary-reinforced structural composites at cryogenic temperatures 2: Advanced composites

The low-temperature mechanical and thermal properties of advanced-fibre reinforced structural composites are reviewed. The magnitude and range of particular properties are discussed with respect to composite type and temperature. A property-material cross reference is given with a 128-entry bibliography. This is Part 2 of a two-part series Part 1 considered glass-reinforced composites.

Evidence for a transition from strong to weak ferromagnetism in Ni-Fe alloys from an investigation on ternary (Ni-Fe)C alloys

The effect of a carbon impurity on the low-temperature magnetic, electric and thermal properties of FCC Ni1-eFec alloys (0<or=C<or=0.65) has been investigated with special emphasis on the higher iron concentration range. The results are as a whole in good agreement with a transition from strong to weak ferromagnetism at the vicinity of the equiatomic composition, and with a strong perturbation of the 'd' states of the matrix by the valence electrons of carbon.

3-Methylpentane and 3-methylheptane: Low-temperature thermodynamic properties

The low-temperature thermal properties of 3-methylpentane and 3-methylheptane were measured by adiabatic calorimetry from 10 to 330 K and 10 to 380K, respectively. Properties measured included the heat capacity of the condensed phases, enthalpy of fusion, triple point temperature, and purity of sample. The results were used to calculate the following thermodynamic functions at selected temperatures for the solid and liquid phases: − { G s ( T ) − H °(0)}/ T , { H s ( T ) − H °(0)}/ T , H s ( T ) − H °(0), S s , and C s . The entropies in the ideal gas state at 298.15 K were computed, and methylene increments of 7.69 cal th K −1 mol −1 for the liquid state and 9.23 cal th K −1 mol −1 for the vapor state were derived. Crystallization of the 3-methylpentane sample was induced (apparently for the first time) by cooling the liquid through the liquid-to-glass transition temperature (about 77 K), followed by slow warming to temperatures between the transition and the triple point (110.25 K).

Frequency Spectrum and Low-Temperature Specific Heat of Noncrystalline Solids

It is shown that an extra phonon density of states associated with the roton-like part of the dispersion of phonon excitations, which is likely to exist in almost all types of noncrystalline solids, gives rise to an excess low-temperature specific heat. This could account for the anomaly in the low-temperature thermal properties observed in a large number of noncrystalline solids and glassy polymers. It is shown that under certain conditions the excess low-temperature specific heat is nearly proportional to absolute temperature.

Contribution to the theory of spin wave conductivity in non-metallic ferro- and ferrimagnets

The low temperature thermal properties of insulating ferro- and ferrimagnetic crystals containing an arbitrary concentration of randomly located magnon scattering centers are found for slab, cylindrical or prismatic samples. The magnon distribution function, energy density, and thermal conductivity are evaluated by analytically solving the non-linear Boltzmann equation. The scattering cross section is energy-dependent and anisotropic, and the magnon dispersion relation includes the effects of crystalline anisotropy, demagnetizing fields, and an external magnetic field. Theory and experiment are compared for yttrium iron garnet.

Low-temperature thermal properties of 2-methylheptane and 2-methyldecane: the thermodynamic properties of the 2-methylalkanes

Experimental measurements were made of the low-temperature thermal properties of 2-methylheptane and 2-methyldecane from 12 to 360 K and 12 to 390 K, respectively. From these measured values and data from the literature the following chemical thermodynamic properties were calculated at selected temperatures for the condensed phases of 2-methylbutane, 2-methylpentane, 2-methylhexane, 2-methylheptane, and 2-methyldecane: Gibbs energy function, enthalpy function, enthalpy, entropy, and heat capacity. The entropies of 2-methylheptane and 2-methyldecane in the ideal gas state at 298.15 K were calculated and methylene entropy increments obtained for the 2-methylalkanes, C 5 to C 11 .

Hexafluorobenzene and 1,3-difluorobenzene low-temperature calorimetric studies and chemical thermodynamic properties

The low-temperature thermal properties of hexafluorobenzene and 1,3-difluorobenzene were measured by adiabatic calorimetry from 13 to 342 K and 11 to 355 K, respectively. The properties measured were heat capacities of solid and liquid, enthalpies of fusion, triple point temperature, and purity, and, in addition, for 1,3-difluorobenzene, the enthalpy and temperature of a solid-solid transition. From these results the following chemical thermodynamic functions were calculated for the condensed phases at selected temperature: Gibbs energy function, enthalpy function, enthalpy, entropy, and heat capacity. For 1,3-difluorobenzene the entropies in the ideal gas state were calculated at several temperatures, a revised vibrational assignment was made from Raman and infrared frequencies reported in the literature, and the chemical thermodynamic functions in the ideal gas state were calculated from 0 to 1500 K. Values of the Gibbs energy of formation and logarithm of equilibrium constant of formation for 1,3-difluorobenzene were also computed for the range 0 to 1500 K.

Trimethylamineborane and triethylamineborane: low-temperature thermodynamic properties

The low-temperature thermal properties of trimethylamineborane and triethylamineborane were determined by adiabatic calorimetry over the range 12 to 390 K and 12 to 310 K, respectively. The quantities measured include the heat capacity of the condensed phases, enthalpies of transition, transition temperatures, enthalpies of fusion, and triple-point temperatures. The results were used to calculate the following thermodynamic functions at selected temperatures for the solid and liquid phases: (G s − H 0 o) T , (H s − H 0 o) T , H s − H 0 o , S s, and C s. Third law entropies and Gibbs energies of formation in the ideal gas state at 298.15 K for both compounds were computed from the results together with vapor pressures and enthalpies of formation from the literature.

Thermal Properties of Polymers at Low Temperatures

Abstract The existing measurements and theories of the low-temperature thermal properties, heat capacity, and thermal conductivity of polymers are reviewed with particular attention paid to the differences between partly crystalline and amorphous polymers. The most striking feature of the low-temperature heat capacity of polymers is that in the liquid helium temperature range the heat capacity does not depend upon the cube of the temperature as for other solids. Further, only well below 1°K does the heat capacity approach the value predicted on the basis of the sound velocity. This behavior indicates the presence of a small number of low-frequency modes of vibration in the frequency spectrum. The fact that such anomalous behavior seems linearly related to the crystallinity implies that this behavior is associated with the amorphous structure, perhaps with motions of pendent groups within cavities formed in the amorphous structure. The thermal conductivity of semicrystalline and amorphous polymers differs ...

Low-Temperature Thermal Conductivity of Impure Insulators

The low-temperature thermal transport properties of an insulating crystal with an arbitrary concentration of randomly located phonon scattering centers are found for slab geometry. The phonon distribution function, the distribution of temperature, the Kapitza resistance at the boundaries, and the heat flux are evaluated by analytically and numerically solving the complete Boltzmann equation with energy-dependent scattering cross section.

Effects of Radiation-Induced Cross-Links on the Low-Temperature Thermal Properties of Polystyrene

Measurements of the thermal conductivity and heat capacity in the liquid-helium temperature range of polystyrene which was cross linked by exposure to an 80-MeV electron beam are reported. The measurements were performed over a range of cross-linking coefficient from 0 to 12. No significant change in the thermal conductivity was observed, but about a 25% reduction in the heat capacity occurred. The thermal conductivity results are compatible with the existing theory of the thermal conductivity of amorphous polymers, while the heat capacity result is taken to indicate a significant reduction in the ``excess heat capacity'' associated with nonacoustic, low-frequency modes.

2,3-Dithiabutane, 3,4-Dithiahexane and 4,5-Dithiaoctane: Chemical Thermodynamic Properties from 0 to 1000°K.1

Thermodynamic properties of the first three members of the symmetrical alkane disulfide series were investigated. Measurements were made of the heat of vaporization and vapor heat capacity of 2,3-dithiabutane; the low temperature thermal properties, vapor pressure and entropy of 4,5-dithiaoctane; and the heats of combustion and formation of 2,3-dithiabutane, 3,4-dithiahexane and 4,5-dithiaoctane. The new experimental data were used in revising previously published tables of thermodynamic functions for 2,3-dithiabutane and 3,4-dithiahexane. A table of thermodynamic functions for 4,5-dithiaoctane was calculated by an incremental method. Values of the heat, free energy and logarithm of the equilibrium constant of formation between 0 and 1000/sup 0/K were computed for the three compounds. The S-S thermochemical bond energy is the same in the three disulfides as in S/sub 3/ within experimental uncertainty.

Cycloheptane, Cycloöctane and 1,3,5-Cycloheptatriene. Low Temperature Thermal Properties, Vapor Pressure and Derived Chemical Thermodynamic Properties

From determinations of the low temperature thermal properties and vapor pressure of cycloheptane, cyclooctane and 1,3,5-cycloheptatriene, values of the entropy in the liquid and vapor states and the heat of vaporization, all at 298.16/sup 0/K, were obtained. These results and values of the heats of formation derivable from literature data were used to compute values of ..delta..Hf/sup 0/, ..delta..Ff/sup 0/, ..delta..Sf/sup 0/ and log/sub 10/ Kf for all three compounds in the liquid and vapor states at 298.16/sup 0/K. In the solid state the thermal behavior of each substance is complex; there are transitions between four different crystalline forms of cycloheptane, three of cyclooctane and two of 1,3,5-cycloheptatriene.