First principle studies on structural,electronic, elastic,optical, and thermoelectric properties of XGeCl3 (X = Rb/Cs): Promising compounds for green energy application

This study employed density functional theory (DFT) embedded in Wien2K code to evaluate the physical features of the XGeCl₃ (X = Rb/Cs) cubic halide perovskites. The structural optimization has been performed considering generalized gradient approximation (GGA) and electronic properties have been computed considering modified Becke-Johnson potential (mBJ). The formation energy and phonon dispersion analysis establish the stability of the investigated compounds. Mechanical stability is further confirmed by the computed diverse elastic coefficients. It has been discovered that the examined substances are naturally ductile. The refractive index, reflectivity, and absorption coefficient, are among the optical parameters that have been estimated and analyzed. Interesting results have been obtained for the transport properties of XGeCl₃ (X = Rb/Cs). The XGeCl₃ (X = Rb/Cs) exhibits a high Seebeck coefficient (X = Rb/Cs) and the largest figure of merit (about 0.99), indicating significant potential for thermoelectric applications.     

Excess thermodynamic parameters of binary mixtures of methanol,ethanol, 1-propanol,and 2-butanol + chloroform at (288.15–323.15 K) and comparison with the Flory theory

In this work we used the experimental result for calculating the thermal expansion coefficients α, and their excess values α ^E , and isothermal coefficient of pressure excess molar enthalpy and comparison the obtain results with Flory theory of liquid mixtures for the binary mixtures {methanol, ethanol, 1-propanol and 2-butanol-chloroform} at 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 K. The excess thermal expansion coefficients α ^E and the isothermal coefficient of pressure excess molar enthalpy ((∂H _m^E/∂P) _T,x for binary mixtures of {methanol and ethanol + chloroform} are S-shaped and for binary mixtures of {1-propanol and 2-butanol + chloroform} are positive over the mole fraction. The isothermal coefficient of pressure excess molar enthalpy (∂H _m^E/∂P) _T,x , are negative over the mole fraction range for binary mixture of {1-propanol and 2-butanol + chloroform}. The calculated values by using the Flory theory of liquid mixtures show a good agreement between the theory and experimental.     

Structural,Thermodynamic and Transport Troperties of Liquid Noble and Transition Metals

Abstract

We have investigated a number of structural, thermodynamic and atomic transport properties of various liquid noble and transition metals. The underlying theory combines a simple form of the N-body potential and the thermodynamically self-consistent variational modified hypernetted chain (VMHNC) theory of liquid. The static structure factors calculated by using the VMHNC resemble, as expected, the hard sphere (HS) values. Consequently the HS model is used to calculate thermodynamic properties, viz. the specific heat, entropy, isothermal compressibility and the shear viscosity of liquid Ni, Cu, Ag, and Au. The results are in reasonable accord with the experimental values.     

Bulk properties of a liquid phase mixture {ethylene glycol+<Emphasis Type="Italic">tert</Emphasis>-butanol} in the temperature range 278.15–348.15 K and pressures of 0.1–100 MPa. II. Molar isothermal compressibility,molar isobaric expansibility,thermal pressure coefficient,and internal pressure

Based on the experimental data, the molar isothermal compressibilities, molar isobaric expansibilities, thermal pressure coefficients, internal pressures of a liquid phase mixture {ethylene glycol (1) + tert-butanol (2)} are calculated for a wide spectrum of compositions in the range of pressures of 0.1–100 MPa and temperatures of 278.15–323.15 K. Shown that the dependences of molar isothermal compressibilities K _{T, m} , molar isobaric expansibilities E _{P, m} , and isochoric thermal pressure coefficients β on the mole fraction of tert-butanol in the mixture are characterized by the absence of extrema typical of aqueous systems. The manifestation of negative partial expansibility and negative partial expansibility of ethylene glycol in the mixture is found. The thermal pressure coefficients decrease with an increase in the mole fraction of tert-butanol at all pressures and temperatures. A rise in the pressure increases the thermal pressure coefficient, while a rise in the temperature decreases its value due to a decrease of free space in the mixture. An increase in the concentration of tert-butanol leads to an increase in the negative temperature coefficient of internal pressure ΔP _int/ΔT, which indicates a weakening of intermolecular interaction at these compositions.     

Viscosity and thermal conductivity of some refrigerants at moderate and high densities on the basis of Rainwater–Friend theory and the corresponding states principle

The initial density dependence of viscosity and thermal conductivity was formulated on the basis of Rainwater–Friend (RF) theory. In this work, we have first focused on the calculation of viscosity and thermal conductivity of moderately dense argon by using RF theory and an accurate ab initio potential function. This theory which was originally presented for spherical potentials have been adapted for calculation of viscosity and translational contribution of thermal conductivity of some refrigerants by introducing the corresponding states correlations for the second transport virial coefficients. Then the internal states contribution for the thermal conductivity has been determined based on the Mason–Monchick and modified Enskog theories. So, we have calculated the viscosity and thermal conductivity of some refrigerants, R32, R14, R12, R13, R22, R134a, R143a, R125, R123, R142b, at moderate densities up to about 2 mol dm⁻³. At high densities, beyond the validity range of RF theory, we have applied correlation expressions for the viscosity and thermal conductivity residual functions to calculate the viscosity and thermal conductivity of supercritical refrigerants and then compared with the available experimental data. In conclusion, we have shown that the RF theory in conjunction with the corresponding states residual functions present the reliable model for calculation of viscosity and thermal conductivity of refrigerants over a comparatively wide temperature and pressure range up to 65 MPa within the experimental errors.     

Thermal decomposition reactions and kinetic parameters of nitritobismuthates(III)

Thermal studies have been carried out on nitritobismuthates(III) of the silver group having the general formula M₂Ag[Bi(NO₂)₆] where M = Cs, Rb, K, and the sodium group having the formula M₂Na[Bi(NO₂)₆] where M = Cs, Rb.Typical thermal curves, temperatures of the endothermic peaks and percentage weight loss, calculated from the TG curve, are shown. On the basis of the results of thermal and X-ray analysis the mechanisms of the thermal decomposition reaction were determined for nitritobismuthates(III).The thermal curves were used to calculate kinetic parameters, activation energy E_a and order of reaction n by Zsako's and Coats and Redfern's methods. A comparison of the thermal stabilities of the salts under study was made. Within the same group of nitritobismuthates(III), the activation energy and the decomposition temperatures of the salts increases when the difference between the radii of outer sphere cations increases.     

Hard-wall potential function for transport properties of alkali metal vapors

This study demonstrates that the transport properties of alkali metals are determined principally by the repulsive wall of the pair interaction potential function. The (hard-wall) Lennard-Jones (LJ) (15-6) effective pair potential function is used to calculate the transport collision integrals. Accordingly, reduced collision integrals of K, Rb, and Cs metal vapors are obtained from the Chapman-Enskog solution of the Boltzmann equation. The law of corresponding states based on the experimental transport reduced collision integral is used to verify the validity of a LJ(15-6) hybrid potential in describing the transport properties. LJ(8.5-4) potential function and a simple thermodynamic argument with the input PVT data of liquid metals provide the required molecular potential parameters. Values of the predicted viscosity of monatomic alkali metal vapor are in agreement with typical experimental data with average absolute deviations of 2.97% for K in the range of 700-1500 K, 1.69% for Rb, and 1.75% for Cs in the range of 700-2000 K. In the same way, the values of predicted thermal conductivity are in agreement with experiment within 2.78%, 3.25%, and 3.63% for K, Rb, and Cs, respectively. The LJ(15-6) hybrid potential with a hard-wall repulsion character conclusively predicts the best transport properties of the three alkali metal vapors.     

Electronic structure and quadrupole interactions in triple molybdates Li<Subscript>2</Subscript>M<Subscript>3</Subscript>Al(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>, M = Cs,Rb

Within the density functional theory the electronic structure of triple molybdates Li₂M₃Al(MoO₄)₄, where M = Cs, Rb, is studied for the first time. It is found that all molybdates studied belong to wide band insulators with a band gap of ~4 eV. Quadrupole frequencies and asymmetry parameters of the electric field gradient near magnetic ⁷Li, ²⁷Al, ⁸⁷Rb, and ¹³³Cs nuclei are calculated and experimental NMR spectra are interpreted.     

Vapour pressures and osmotic coefficients of binary mixtures of 1-ethyl-3-methylimidazolium ethylsulfate and 1-ethyl-3-methylpyridinium ethylsulfate with alcohols at T = 323.15 K

Osmotic coefficients of binary mixtures containing alcohols (ethanol, 1-propanol, and 2-propanol) and the ionic liquids 1-ethyl-3-methylimidazolium ethylsulfate and 1-ethyl-3-methylpyridinium ethylsulfate were determined at T = 323.15 K. Vapour pressure and activity coefficients of the studied systems were calculated from experimental data. The extended Pitzer model modified by Archer, and the modified NRTL model (MNRTL) were used to correlate the experimental data, obtaining standard deviations lower than 0.012 and 0.031, respectively. The mean molal activity coefficients and the excess Gibbs free energy of the studied binary mixtures were calculated from the parameters obtained with the extended Pitzer model of Archer.     

The calculation of Cs and Rb conductivities in the region of liquid–plasma transition

The conductivity and thermal conductivity of Cs and Rb are calculated in the liquid phase and in the region between the plasma (gas) and the liquid states. The last area is located at the temperatures higher than the critical one, near the critical point. The Ziman formalism originated from the liquid metal theory was used for the calculations. The results of present calculations were compared with available experiments and calculations of other researchers. It was found that the liquid state formalism can be applied to expanded liquid Cs and Rb at densities higher than the critical one, but another type of models is necessary at lower densities.     

Fission yield measurements of Rb,Sr, Cs and Ba isotopes far from the center of the isotopic yield distributions in 235U(nth,f)

Independent fission yields of ^92–99Rb, ^94–100Sr, ^142–148Cs and ^143–149Ba in the thermal neutron fission of ²³⁵U were determined at the SOLIS on-line mass separator. The independent fission yields of ⁹⁹Rb, ^{147, 148}Cs and ^145–149Ba were measured for the first time. For all the elements a “wing effect” is apparent, i.e. the experimental independent fission yields in the wings of the isotopic (isobaric) yield distributions are considerably higher and their decline with mass (charge) less steep than predicted by fission yield systematics. To account for this effect a corrected semi-empirical distribution function for fission yields is proposed. Comparison of the experimental fission yields with the predictions of theoretical fission models also shows the existence of the “wing effect”. Since the theory predicts primary fission yields a correction due to prompt neutron emission was calculated. It is shown that the effect of prompt neutron emission is to broaden the isotopic distributions in the wing of heavy isotopes only slightly, and in the wing of light isotopes more significantly, but it does not explain the “wing effect” which seems to originate in the fission process.     

Ab initio calculation of structural,lattice dynamical,and thermal properties of cubic silicon carbide

We present first-principles calculations of the structural, lattice dynamical, and thermal properties as well as Raman results for cubic silicon carbide (3C SiC). The plane-wave pseudopotential approach to density functional theory (DFT ) in the local density approximation has been used to calculate the equilibrium properties of 3C SiC, i.e., the ground-state energy, the band structure, the valence electron density, the lattice constant, the bulk modulus, its pressure derivative, and the ionicity factor of the chemical bonds. The linear-response theory within DFT has been used to obtain the phonon frequencies, the eigenvectors, and the mean-square atomic displacements. Furthermore, we calculated the mode Grueisen parameters, the internal-strain parameter, the elastic constants, the Born effective charge, and the high-frequency dielectric constant. The specific heat at constant volume and at constant pressure, the thermal expansion coefficient, the temperature dependence of the lattice constant, and that of the isothermal and adiabatic bulk modulus have been derived within the quasi-harmonic approximation. Finally, the second-order Raman spectrum of 3C SiC has been calculated using phenomenological polarizability coefficients and ab initio frequencies and eigenvectors. © 1995 John Wiley & Sons, Inc.     

Measurement and modeling of osmotic coefficients of binary mixtures (alcohol + 1,3-dimethylpyridinium methylsulfate) at T = 323.15 K

Measurement of osmotic coefficients of binary mixtures containing several primary and secondary alcohols (1-propanol, 2-propanol, 1-butanol, 2-butanol, and 1-pentanol) and the pyridinium-based ionic liquid 1,3-dimethylpyridinium methylsulfate were performed at T = 323.15 K using the vapor pressure osmometry technique, and from experimental data, vapor pressure, and activity coefficients were determined. The extended Pitzer model modified by Archer, and the NRTL model modified by Jaretun and Aly (MNRTL) were used to correlate the experimental osmotic coefficients, obtaining standard deviations lower than 0.017 and 0.054, respectively. From the parameters obtained with the extended Pitzer model modified by Archer, the mean molal activity coefficients and the excess Gibbs free energy for the studied binary mixtures were calculated. The effect of the cation is studied comparing the experimental results with those obtained for the ionic liquid 1,3-dimethylimidazolium methylsulfate.     

The thermal properties of Al–Mg–TM (TM = Sc,Zr): Ab initio study

Ab initio density functional theory (DFT) and density function perturbation theory (DFPT) have been used to investigate the thermal properties of the Al–Mg–Sc, Al–Mg–Zr and Al–Mg–Sc–Zr alloys over a wide range of temperature and pressure. Phonon dispersions are obtained at equilibrium and strained configurations by DFPT. Using the quasiharmonic approximation (QHA) for the free energy, several physical quantities of interest such as thermal Grüneisen parameter, heat capacity at constant pressure and at constant volume, thermal expansion coefficient, entropy, adiabatic bulk modulus and isothermal bulk modulus as a function of temperature and pressure are calculated and discussed. The present results show that the thermal expansion coefficient of the Al–Mg–Sc–Zr is far lower than that of Al–Mg–Sc and Al–Mg–Zr, and the variation features in the adiabatic bulk modulus and isothermal bulk modulus for the Al–Mg–Sc–Zr are also very different from that of Al–Mg–Sc and Al–Mg–Zr.     

Pressure–volume–temperature behavior of two polycyanurate networks

The pressure–volume–temperature (PVT) behavior was studied for two polycyanurate networks having different crosslink densities using a pressurizable dilatometer. The samples were studied at temperatures ranging from 60 to 180 °C and at pressures up to 170 MPa to yield PVT data in both rubbery and glassy states. The Tait equation is found to well describe the isobaric temperature scan and isothermal pressure scan data. The thermal expansion coefficients, instantaneous bulk moduli, and thermal pressure coefficients are extracted from the data and their dependence on crosslink density is examined. The time‐dependent viscoelastic bulk modulus (K(t)) is also calculated in the vicinity of the α‐relaxation from previously published pressure relaxation experimental data, and the strength and shape of the dispersion are found to be independent of crosslink density. The limiting bulk moduli depend strongly on temperature with those of the more loosely crosslinked sample being lower at a given temperature and pressure, although at T_g(P), the limiting moduli of the more loosely crosslinked sample are slightly higher than those of the more highly crosslinked sample. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Empirical Relationships between Transport Coefficients of Liquid Metals over a Range of Thermodynamic States

Abstract

Assuming the Wiedemann-Franz law, measured data for electrical conductivity α of liquid Cs and Rb is converted to λ_e , the electronic contribution to the thermal conductivity A. While the major part of the measured thermal conduction is thereby accounted for, the “residual” ionic contribution, denned as (^λ-1—λ_e ^?1)^?1, does not simply increase as the metal-insulator transition is approached along the coexistence curve.

Since λ is dominated by _λe, it is surprising that a hard sphere model, which predicts λ/n = 5k_B/2M with n the shear viscosity and M the ionic mass, still gives correctly a relatively constant ratio, though a difference in behaviour of λ/n as a function of thermodynamic state is noted for liquid Rb and Cs compared with liquid argon.

A generalization of Andrade's formula for shear viscosity at the melting point is also discussed, including the work of Zwanzig relating the self-diffusion coefficient D to n via the bulk viscosity.     

Low-coordination phases of both crystalline and fluid states of alkali metals under extreme conditions of high and low densities,respectively

After a brief summary of early work, involving the present authors, relating to low coordination phases of some alkalis in either dense crystalline states at high pressure (e.g. Li) or low density metallic fluids near criticality (Cs and Rb), contact is made with the very recent density functional study by Pickard and Needs (Phys. Rev. Lett. 102, 146401 (2009)). Whereas these authors predict three- and four-fold coordination numbers for extremely high pressure crystalline phases of Li, we stress here the remarkable behaviour of the heavy alkali metallic fluids Cs and Rb along the liquid–vapour coexistence curve towards the critical point. Coordination numbers ～8?10 near melting then reduce, as the density is lowered, to 2 at or near the critical point.     

Osmotic coefficients of binary mixtures of four ionic liquids with ethanol or water at T = (313.15 and 333.15) K

Measurements of osmotic coefficients of BmimCl (1-butyl-3-methylimidazolium chloride) and HmimCl (1-hexyl-3-methylimidazolium chloride) with ethanol and EmimEtSO₄ (1-ethyl-3-methylimidazolium ethylsulfate) and EmpyEtSO₄ (1-ethyl-3-methylpyridinium ethylsulfate) with water at T = (313.15 and 333.15) K are reported in this work. Vapour pressure and activity results of the studied binary systems are obtained from experimental measurements. The results for the osmotic coefficients are correlated using the extended Pitzer model modified by Archer and the modified NRTL (MNRTL) model. The standard deviations obtained with both models are also given. The parameters obtained with the extended Pitzer model of Archer are used to calculate the mean molal activity coefficients.     

The relationship between the thermal expansions and structures of ABO4 oxides

The linear thermal expansion coefficients of ABO₄ compounds are determined and the expansion tendency is analyzed from the chemical bond viewpoint. All chemical bonds contributions are involved. The contributions from different chemical bonds are compared with each other and the origin of the expansion behavior of ABO₄ oxides is revealed that the A-O bonds expansions dominate the compound expansion. The calculated expansion coefficients agree satisfactorily with the experimental data. By analyzing the expansion regularity the range of the expansion coefficients can be qualified. The thermal expansion coefficients of some ABO₄ compounds having not been measured are predicted and discussed.     

Osmotic coefficients of binary mixtures of 1-butyl-3-methylimidazolium methylsulfate and 1,3-dimethylimidazolium methylsulfate with alcohols at T = 323.15 K

Measurements of osmotic coefficients of BMimMSO₄ (1-butyl-3-methylimidazolium methylsulfate) and MMimMSO₄ (1,3-dimethylimidazolium methylsulfate) with ethanol, 1-propanol, and 2-propanol at T = 323.15 K are reported in this work. Vapour pressure and activity values for the binary systems studied are obtained from experimental results. The osmotic coefficients are correlated using the extended Pitzer model modified by Archer and the modified NRTL (MNRTL) model. The standard deviations obtained with both models are lower than 0.013 and 0.060, respectively. The parameters obtained with the extended Pitzer model of Archer are used to calculate the mean molal activity coefficients and the excess Gibbs free energy of the binary mixtures.