Victor N. Naumov

Low-temperature heat capacity of heulandite: comparison with clinoptilolite

Abstract Low-temperature heat capacity of heulandite Na 0.365 K 0.059 Ca 0.861 Al 2.138 Si 6.860 O 18 ·6.17H 2 O was measured in an adiabatic vacuum calorimeter. The results obtained were compared with those for heulandite and clinoptilolite from literature. The errors in measurements of the water content are shown to be the main reason of discrepancies among the data on heat capacities for the zeolites. The random error can be as high as 1.1%. The greatest systematic error of 2.5% was shown to be in the heat capacities of clinoptilolite. Unusual temperature dependence has been recognized in published data on heat capacity of clinoptilolite, as if free electrons are there in a silicate. Heat capacity of four different species of heulandite–clinoptilolite series are known. However, the data published do not enable one to recognize the relationship between heat capacity and a composition.

The extraction of phonon and electron properties from experimental heat capacity with new approximation based on high temperature expansion

Abstract A new approach to the high temperature expansion of heat capacity C ( T ) is proposed. The lattice heat capacity is described by two first terms of this expansion with characteristic temperatures ( θ 2 and θ 4 ) plus a remainder. The latter is approximated by some function with only parameter θ ∗ which is attributed to the upper limit of a phonon spectrum. This new form of expansion extends downwards along the range of a good approximation of a lattice heat capacity in comparison with ordinary truncated high temperature expansion. This, in turn, allows investigation of the new phenomena in some substances. This method was tested on several model curves C ( T ) with the phonon spectrum known in advance. The examples of the determination of phonon and electron characteristics for dielectrics, metals and high temperature superconductors are shown.

Electron heat capacity and moments of phonon density of states of HoBa2Cu3O7−δ

Abstract The heat capacity of superconducting HoBa2Cu3O7−δ ceramics has been measured in the temperature interval 14–315 K. The electron component of the heat capacity γT was separated in the normal-state region (above Tc). The special technique for separating the heat capacity into phonon and electron components was used. Besides the γ value, the numerical values of the second moment Θ2, of the fourth moment Θ4 and of the moment Θ ∗ attributed to the upper limit of the phonon density of states were obtained. The obtained moments appear to be somewhat smaller than the analogous ones for YBCO. This decrease characterizes the phonon spectrum softening owing to the substitution of a light ion, Y, by a heavy ion, Ho. The obtained moments allow one to calculate precisely the heat capacity at constant volume Cv(T) in the temperature region T>Θ ∗ 2π .

Correlation between Entropy and Structural Characteristics of Metal tris-Acetylacetonates

AbstractThe heat capacity of aluminum tris-acetylacetonate Al(C5H7O2)3 was measured over the temperature range 8–321 K by adiabatic calorimetry. The data obtained were used to calculate its thermodynamic functions (entropy, enthalpy, and reduced Gibbs energy). Correlation between entropy at 298.15 K and unit cell volume was observed for metal β-diketonates of the acetylacetonate group.

Thermodynamic study of compounds of the Nd-Ba-Cu-O system

Standard enthalpies of formation for solid solutions of composition Nd1 + xBa2 − xCu3Oy (x = 0–0.8, y = 6.65–7.24) from oxides were determined by solution calorimetry. The heat capacity of NdBa2Cu3O6.87 phase was measured in the range 5–320 K by low-temperature adiabatic calorimetry. The absolute entropy So(T), the difference of enthalpies Ho(T)-Ho(0 K), and the reduced Gibbs energy Φo(T) = So(T)–[Ho(T)–Ho(0)]/T were calculated on the basis of smoothed dependence Cp(T) in the 0–320 K range. An assessment was made for the heat capacities and the absolute entropies of solid solutions Nd1+xBa2−xCu3Oy. The obtained set of thermodynamic parameters can be used for the calculation of phase equilibria in the Nd-Ba-Cu-O system.

Heat capacity peculiarity of 90 K samples of YBa2Cu3O6+x above Tc

Abstract The temperature dependence of heat capacity of superconducting YBa 2 Cu 3 O 6+ x system (with x =0.85, 0.90, 0.95) was investigated above T c . For all the samples the “small” anomalies were discovered in ranges 110–180 K ( T low ), 205–235 K ( T m ) and 250–290 K ( T h ). The analysis with involving data for TmBa 2 Cu 3 O 6.95 and GdBa 2 Cu 3 O 6.95 reveals that one may consider some of these anomalies as a characteristic property of the 90 K samples.