Characteristics of the thermodynamics of the electronic subsystem in intercalated titanium dichalcogenides

Results of an electrochemical experiment are used to calculate the concentration dependences of the chemical potential and entropy of silver in Ag_xTiTe₂. It is shown that the electronic contribution to the thermodynamic functions must be taken into account in any explanation. The thermodynamic functions are modeled and the density of states in the conduction band is refined. It is confirmed that a band of localized states exists near the Fermi level, as was hypothesized previously to explain kinetic experiments. Various mechanisms are considered for the formation of these localized states. Fiz. Tverd. Tela (St. Petersburg) 40, 1187–1189 (July 1998)     

Structure of the mantle discontinuities

Abstract

The results of thermodynamic calculations in the FeO-MgO-SiO₂ (FMS) system show that the elastic properties and density across the 400-km discontinuity might be consistent with a transition zone of isochemical pyrolite composition and do not require chemical stratification. However, phase changes in pyrolite do not explain the 650-km discontinuity.     

On the deconfinement phase transition in the resonance gas

We obtain the constraints on the governing parameters of the dense hadronic gas model at the critical temperature and propose quasiuniversal ratios of the thermodynamic quantities. The possible appearance of thermodynamic instability is discussed. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 487–491 (10 April 1996) Alexander von Humboldt Fellow. Published in English in the original Russian journal. Edited by Steve Torstveit.     

Thermodynamic theory of the equation of state of materials

A universal derivation of the thermodynamic equations on the basis of a combined analysis of the exact relations for any material — the virial theorem, the shock adiabat, and the differential thermodynamic identity relating the thermic and caloric equations of state of matter — is given. This combination makes it possible to reduce the fundamental problem of thermodynamics to a boundary-value problem of mathematical physics. Analytic relations T _s=T(P _s,ρ _s and T _s=T(D,u) are obtained for classical systems. Zh. Tekh. Fiz. 68, 1–9 (October 1998)     

Inhibition of the growth of excrescences in mixed electronic-ionic conductors

The thermodynamic aspects of the diagnosis, prevention, and inhibition of the growth of excrescences in mixed electronic-ionic conductors are considered in the case of the representative material copper selenide. Zh. Tekh. Fiz. 68, 67–71 (November 1998)     

The melting line of the WCA lennard-jones reference system

Abstract

The Melting line of the WCA L-J reference system, i.e. the part of the L-J potential representing the repulsive forces, is determined by means of Monte Carlo calculations. The Gibbs free energy of the fluid is calculated by thermodynamic integration and that of the solid by using the Einstein-crystal method of Frenkel and Ladd (1984).     

The statistical theory of the condensed system equation of state at high pressures

Abstract

One of the main problems in the statistical physics of condensed systems is the problem of the adequate equation of state to describe the thermodynamical properties of the substance in the wide range of pressure values. Here it is being solved by means of thermodynamic perturbation theory and the integral equations of the statistical theory of dense gases and liquids.     

Nearest-neighbor two-point correlation function of the Z-invariant eight-vertex model

The nearest-neighbor two-point correlation function of the Z-invariant inhomogeneous eight-vertex model in the thermodynamic limit is computed using the free-field representation. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 243–247 (10 August 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Low-temperature specific heat of CeAl2 at high pressures

Abstract

We have obtained new data of the low-temperature specific heat of CeAl₂ under pressure with the aim to complete the phase diagram and to solve an existing discrepancy between results of magnetic and thermodynamic measurements.     

Thermodynamics of self-assembly of sodium octanoate: comparison with a fully fluorinated counterpart

The isotherms of conductivity of sodium octanoate were measured and the critical micelle concentration (cmc) and degree of ionization of the micelles, β, determined in a range of temperatures (273–343 K) above the Krafft point. The thermodynamic parameters, Gibbs free energy ΔG _m ⁰, enthalpy ΔH _m ⁰, and entropy ΔS _m ⁰ of micelle formation, were determined from polynomial adjustments of the temperature dependence of cmc and from a proposed thermodynamic model based on the works of Muller [1993, Langmuir, 9, 96] and Rodríguez et al. [2002, J. Colloid Interface Sci., 250, 438]. The increase in heat capacity upon micellization, ΔC _pm ⁰, was estimated from the parameters of the model and the enthalpy—entropy compensation phenomena discussed. Finally, for information on their structural differences, hence to understand their different behaviours, thermodynamic parameters are discussed, comparing the corresponding fluorocarbon compound. A remarkable shift in minimum temperature in the U-shaped curve of cmc versus temperature was found when hydrogen was substituted by fluorine in the hydrophobic chain of the surfactant. This behaviour is a consequence of the special characteristics of the fluorine substituent in the hydrophobic tail and was reflected in the thermodynamic parameters and in the enthalpy—entropy compensation parameters, presenting different intercepts at the same compensation temperature.     

Transition states in the melting of germanium in dynamic and quasistatic regimes

The conditions under which transition states arise and exist during the melting of germanium are identified by digital differential-thermal analysis. The pre-and postmelting cooperative effects arising under real conditions in dynamic and quasistatic regimes are nonequilibrium phase transitions and can be characterized by a system of thermodynamic parameters. Instability of the thermodynamic parameters of the transition states is observed in quasistatic regimes as a result of dynamic instability. The system of parameters introduced characterizes the formation of a special phase state — pre-and postmelting mesophases. Zh. Tekh. Fiz. 69, 57–61 (December 1999)     

The method of moments and the nonequilibrium thermodynamics of rarefied gases

A generalized variant of the nonequilibrium thermodynamics of rarefied gases based on the linearized equations of Grad’s method of moments is studied. It is shown that despite the more complicated form of the thermodynamic forces, which include spatial derivatives of the fluxes, entropy production remains a bilinear combination of generalized thermodynamic fluxes and forces. Using perturbation theory in the small Knudsen number, the expressions obtained can be reduced to the well-known results of the Chapman-Enskog method at the level of the linearized Burnett approximation. Zh. éksp. Teor. Fiz. 113, 2081–2095 (June 1998)     

On Quantum Systems of Particles with Singular Magnetic Interaction

Abstract

For systems of particles with singular magnetic interation for special choice of a selfadjoint extension of the Hamiltoniam equilibrium reduced density matrices are calculated in the thermodynamic limit for simplest pair magnetic potentials.     

Size effect on thermodynamic properties of free nanocrystals

We demonstrate that the discrete character of the vibrational spectrum of a small crystal accounts for size dependence of its thermodynamic properties and melting temperature. Using a self-consistent statistical method [Phys. Rev. B 66, 054302 (2002)] we derive the Gibbs free energy of free nanocrystalline plates and calculate the thermodynamic parameters as functions of plate thickness for Cu.     

A thermodynamic basis for the electronic properties of molten semiconductors: the role of electronic entropy

Abstract

The thermodynamic origin of a relation between features of the phase diagrams and the electronic properties of molten semiconductors is provided. Leveraging a quantitative connection between electronic properties and entropy, a criterion is derived to establish whether a system will retain its semiconducting properties in the molten phase. It is shown that electronic entropy is critical to the thermodynamics of molten semiconductor systems, driving key features of phase diagrams including, for example, miscibility gaps.     

High pressure influence on the phase diagram construction of 3-d transition metals with carbon systems

Abstract

The results of experimental studies and thermodynamic calculations of melting diagrams of the 3-d transition metal-carbon systems are discussed in this paper. The authors present their theoretical and experimental results which complement the earlier available data. The Fe-Ni-C, Fe-Co-C, and Mn-Ni-C systems are shown to be suitable for diamond synthesis at relatively low p, T-parameters.     

Thermodynamics of phonon-stabilized Fermi distributions with application to uranium

Since phonons are built on the free energy of electrons, their frequencies can be altered by thermal electronic excitations, implying that thermal electronic excitations can alter the phonon entropy. The effect of this extra phonon entropy on electronic distribution functions and thermodynamic properties is calculated in the limit of classical vibrations. The phonon entropy stabilizes electrons above the Fermi level by more than the usual k _B T. The thermodynamic coupling of electron and phonon degrees of freedom allows far more heat capacity than in equivalent independent systems. The method developed is used to explain uranium data from the literature.     

Magnetostriction of the high-temperature non-cuprate superconductor BaBiKO

Measurements of the magnetostriction of the isotropic high-temperature superconductor Ba_0.66K_0.34BiO₃ revealed an effect of the order of 10⁻⁶ which exceeds that for conventional superconductors but is not as high as the giant magnetostriction of cuprate high-temperature superconductors. A thermodynamic analysis of the results enables comparison with the results of numerical calculations of effects induced by magnetic flux pinning. Fiz. Tverd. Tela (St. Petersburg) 40, 1199–1203 (July 1998)