共查询到20条相似文献,搜索用时 15 毫秒
1.
The effect of germanium addition on the physical properties, i.e. density, molar volume, compactness, number of lone-pair electrons, average coordination number, heat of atomization, mean bond energy, cohesive energy and glass-transition temperature, of (Se80Te20)100? x Ge x (x = 0, 2, 4, 6) bulk glassy alloys was investigated. The density of the glassy alloys is found to decrease with increasing Ge content. The molar volume and compactness of the structure of the glass were determined from the measured density. The mean bond energy is proportional to the glass-transition temperature. The cohesive energy of the samples has been calculated using a chemical bond approach and is correlated with an increase in the optical energy gap with increase in the Ge content. The heat of atomization was also calculated and correlated with the optical energy gap. The glass-transition temperature has been estimated using different methods and is found to increase with an increase of Ge content. 相似文献
2.
Abstract The nonlinear decrease of Gibbs free energy (gF) for the formation of Frenkel defects in Agx accounts for the anomalous increase of electrical conductivity and self-diffusion in this system. Using an analytical expression for gF(T) the excess heat capacity for Frenkel defects is calculated. A comparison with experimental data indicates that all the anomalies of heat capacity at high temperature is not accounted for. A contribution from Schottky defects is thus probable. 相似文献
3.
Crystal structure and thermochemical properties of phase change materials bis(1-octylammonium) tetrachlorochromate
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A new crystalline complex (C8H17NH3)2CdCl4(s) (abbreviated as C8Cd(s)) is synthesized by liquid phase reaction. The crystal structure and composition of the complex are determined by single crystal X-ray diffraction, chemical analysis, and elementary analysis. It is triclinic, the space group is P-1 and Z = 2. The lattice potential energy of the title complex is calculated to be UPOT (C8Cd(s))=978.83 kJ·mol-1 from crystallographic data. Low-temperature heat capacities of the complex are measured by a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K. The temperature, molar enthalpy, and entropy of the phase transition for the complex are determined to be 307.3± 0.15 K, 10.15± 0.23 kJ·mol-1, and 33.05± 0.78 J·K-1·mol-1 respectively for the endothermic peak. Two polynomial equations of the heat capacities each as a function of temperature are fitted by the least-square method. Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials. 相似文献
4.
《Comptes Rendus de l''Academie des Sciences Series IV Physics》2001,2(2):191-202
The marked increase in second-order thermodynamic properties observed at the glass-transition signals the onset of configurational changes in viscous liquids. Experimental determinations in the glass-transition range will illustrate this point for thermal expansivity and demonstrate that the kinetics of volume, enthalpy and structural relaxation are identical for silicate liquids. Within the framework of the Adam–Gibbs theory, heat capacity and viscosity data may be combined to calculate configurational entropies and gain insights into the potential energy barrier to viscous flow. Finally, the considerable effect of water on the glass transition temperature of geologically relevant silicates is presented. 相似文献
5.
P. Ruello L. Desgranges G. Calvarin G. Petot-Ervas 《Journal of Physics and Chemistry of Solids》2005,66(5):823-831
X-ray and neutron powder diffraction studies of UO2 were performed under controlled oxygen partial pressure between room temperature and 1673 K. More than 40 neutron diffraction patterns were recorded. The thermal expansion coefficient of UO2 and the temperature dependence of Debye-Waller factors for oxygen and uranium atoms were determined. The dependence of Debye-Waller factors as a function of temperature is linear and the thermal expansion coefficient follows the classical Debye regime within the temperature range 300-1000 K. Above 1200 K, a departure from this quasi-harmonic behavior is clearly observed. Both an abnormal increase of the thermal expansion and of the oxygen sublattice disorder are evidenced. The departure of the lattice parameter from a linear thermal variation is found to be thermally activated with an effective activation energy close to 1 eV, very similar to the activation energy already found for the electrical conductivity. This new result suggests that polarons may affect the mean lattice parameter. A new thermodynamic model is then proposed to explain the heat capacity thermal variation by only three contributions: harmonic phonons, thermal expansion and polarons. 相似文献
6.
Nanoparticle Distribution in Three‐Layer Polymer–Nanoparticle Composite Films: Comparison of Experiment and Theory
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Astrid Drechsler Peter Friedel Sebastian Rauch Petra Uhlmann Manfred Stamm Reinhold Rennekamp 《Particle & Particle Systems Characterization》2015,32(1):123-131
The distribution of hydrophobic nanoparticles deposited on a hydrophilic polymer film is investigated by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy before and after spin‐coating a polymer solution on the particle film and drying it at room temperature. Various polymers and solvents are used. To reach equilibrium, all investigated systems are annealed additionally above the glass transition temperature (Tg) of the polymers. The compatibility of the interacting components is estimated by calculating their surface energy, solubility, and mutual interaction parameters. The experimental results show a redistribution of the particles on both interfaces of the polymer film. This corresponds to the calculated immiscibility of particles and polymers. The distribution of the nanoparticles at the interfaces is related mainly to the vapor pressure of the solvent, that is, kinetic effects during spin‐coating. Only minor contributions result from surface energy, solubility, and interaction parameters. 相似文献
7.
The high temperature heat capacities of LaSn3 compound and CeSn3 intermediate valence compound have been obtained from enthalpic contents measurements, using the technique of drop calorimetry in the 400–1200 K temperature range.The heat capacity behaviour of CeSn3 has been compared with that of LaSn3 and the quantitative difference between the two trends is explained in terms of residual promotional energy of the 4? electron of Ce to the conduction band. 相似文献
8.
The perturbation theory with non-spherical reference system is used for molecular fluid with angle-dependent square-well type
potential. Simple analytic expressions are given for the thermodynamic properties such as the equation of state, excess free
energy per particle, internal energy and internal heat capacity. The effects of anisotropy on the thermodynamic properties
are discussed. The anisotropy effects increase with increase of density and decrease of temperature and depends on the anisotropy
parameterx
0. 相似文献
9.
M.M. Al Shorman F.S. Nammas H. Haddad A.A. Shukri 《Chinese Journal of Physics (Taipei)》2018,56(3):1057-1063
The thermodynamic properties of two electrons in two dimensional parabolic GaAs quantum dot are studied where both the magnetic field and the e–e interaction are fully considered. The e–e interaction has been treated by a model potential which makes the Hamiltonian exactly solvable. The energy spectrum is used to calculate the canonical partition function, and then we obtain the thermodynamic properties; mean energy, heat capacity and entropy as a function of temperature (T) and magnetic field (B).A steep transition from zero to 4kB is observed in the heat capacity as a function of temperature for small values of magnetic field and saturates within a small temperature range, also the heat capacity has a peak-like structure at low temperature, while for high magnetic field heat capacity develops a shoulder at 2kB then it approaches the saturation value with further increase in temperature. The entropy increases with increasing temperature, but at higher temperature, it remains almost independent of the magnetic field. It is shown that, at low magnetic field values, the effect of magnetic field on heat capacity is tangible and it attains a constant value with further increase in magnetic field. Entropy is almost linearly proportional with increasing magnetic field strength. 相似文献
10.
Peter J. Meschter James W. Wright Charlie R. Brooks Thomas G. Kollie 《Journal of Physics and Chemistry of Solids》1981,42(9):861-871
Heat capacity data for solid nickel have been re-evaluated and analyzed into physical contributions, 0–1726 K. Two new sets of measurements of Cp(Ni), 333–1500 K, have been combined with literature data to produce an evaluated data set with uncertainty ? ± 2%. These smoothed data have been analyzed into vibrational harmonic, electronic, magnetic and dilatational contributions with the aid of auxiliary measurements of expansion coefficient, compressibility, vibrational and electronic densities of states, elastic constants, and magnetic exchange integral and susceptibility obtained from the literature. The vibrational harmonic term is interpreted in terms of a θD-vs-T curve in accord with predictions of the density-of-states distribution. The electronic contribution is smaller than predicted by free-electron theory due to a large electron-phonon effect. The electronic term for paramagnetic nickel is in good agreement with that predicted from band calculations. The magnetic contribution yields a magnetic entropy in accord with theoretical predictions, and a magnetic internal energy and critical-point behavior in agreement with the isotropic Heisenberg model. The experimental heat capacity can be accounted for without reference to vibrational anharmonic and vacancy contributions, in accord with recent calculations. 相似文献
11.
T. Inoue S.G. Sankar R.S. Craig W.E. Wallace K.A. Gschneidner 《Journal of Physics and Chemistry of Solids》1977,38(5):487-497
The heat capacities of the compounds DyAl2, ErAl2 and LuAl2 were measured in an adiabatic calorimeter from approximately 5 to 300 K. The compounds DyAl2 and ErAl2 show CP 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, CL was obtained from the CP data of LuAl2 by a method of interpolation which gave values of CL for an arbitrary R Al2 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 (2J + 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 A12 phases was found to exhibit an exponential dependence below the temperature corresponding to the spin wave energy gap and a T dependence above this temperature.Detailed calculations were performed to characterize the influence of cubic crystal field in ErAl2 on the 4I ground state multiplet of the Er3+ ion. It is concluded that the magnetic ordering in ErAl2 takes place within the Γ83 quartet state. Smoothed values of heat capacity, entropy and related thermodynamic functions are tabulated. 相似文献
12.
M. Madani Nabila A. Maziad Rasha M. Khafagy 《Journal of Macromolecular Science: Physics》2013,52(6):1191-1203
Thermally stimulated depolarization current (TSDC) and thermal analysis studies of gamma irradiated LiOH/PVA blends were done. To study the mechanisms of conduction and TSDC in poly(vinyl alcohol) (PVA) and LiOH/PVA blends, short circuit TSDC at a polarizing temperature 353 K with a polarizing field of 3 kV cm?1 have been analyzed in the temperature range 300–410 K. Two peaks are evident from the global TSDC measurements on the pure PVA homopolymer. Meanwhile, in all blended samples; there is only one broad peak with a shoulder on the high temperature side due to the relaxation of the poly‐blend system. The temperature dependence, 300–408 K, of the current density (J) for pure PVA and its blended samples has been studied. It was observed that J values increase dramatically with increasing temperature (in the low temperature region from 300–340 K) owing to the formation of local ordered regions in the otherwise disordered amorphous matrix of PVA. Further increase in the temperature caused a marginal increase in J values. The temperature dependence of the specific heat for all samples was measured. A linear increase of C p was observed with an increase in temperature, which is ascribed to the increase in lattice vibration of linear macromolecules and consequently, increases in the number of internal degree of freedom of phonons. 相似文献
13.
For the first time, the specific heat of single phase, stoichiometric, high transition temperature (21.8 K) A-15 Nb3Ge has been measured. From the data between 4 and 29 K, the linear term coefficient, γ, of the specific heat is found to be 30.3±1. mJ/mole-K2 and the Debye temperature, ?D, is 302±2 K. The bulk energy gap parameter, 2Δ/kTc, is found to be 4.2±0.2, in agreement with tunneling measurements. 相似文献
14.
T. E. Hargreaves D. F. Brewer S. Chastin C. Chen N. E. Hussey A. Lappas C. S. McMenamin J. Osborne K. Prassides A. L. Thomson 《Czechoslovak Journal of Physics》1996,46(3):1215-1216
A single crystal of La2CuO4 was made superconducting after treatment in a high pressure oxygen furnace. Measurements are presented of the low temperature heat capacity of the insulating crystal in zero field between 1K and 3K, and of the superconducting crystal in fields of 0, 2 and 4 Tesla applied parallel to the ab plane between 0.2K and 3K. A linear heat capacity contribution is observed for the crystal in both the insulating and superconducting states. This linear heat capacity contribution is larger in the superconducting state and is insensitive to the applied magnetic field. 相似文献
15.
Two different procedures for the preparation of bimorph structures within nonlinear optical polymer layers are reported. One technique consists of thermally assisted poling above the glass-transition temperature followed by photo-induced poling below the glass-transition temperature. In this poling scheme, the second step is based on the photoisomerization of the dipole molecules. The other method comprises two consecutive thermally assisted poling steps with opposite field polarity in a double layer of two nonlinear optical polymers with different glass-transition temperatures. Pyroelectric thermal analysis is employed for analyzing the stability of the resulting bimorph structures, while pyroelectric depth profiling allows for a non-destructive qualitative analysis of their polarization distributions. 相似文献
16.
A novel complex bis(1-dodecylammonium) tetrachlorochromate (C12H25NH3)2CdCl4(s) (abbreviated as C12Cd(s)) was synthesized by liquid phase reaction. Crystal structure and composition of the complex were determined by X-ray crystallography, chemical analysis, and elemental analysis. It is triclinic, the space group is P?1 and Z = 2. Lattice potential energy (LPE) of the complex was calculated to be kJ·mol?1 from crystallographic data. Low-temperature heat capacities were measured by a precise automatic adiabatic calorimeter over the temperature range from 78 to 370 K. The temperature, molar enthalpy, and entropy of the phase transition of the complex were determined to be 331.88 ± 0.02 K, 55.79 ± 0.46 kJ·mol?1, and 168.10 ± 1.38 J·K?1·mol?1, respectively. Two polynomial equations of the heat capacities as a function of temperature were fitted by least-square method. Smoothed heat capacities and thermodynamic functions of the complex were calculated. 相似文献
17.
The precise measurements of the specific heat and the linear expansion coefficient of polygrain samples of the ordered icosahedral
phase Al63Cu25Fe12 have been performed in the temperature range 1.8–400.0 K. The deviations from the Grüneisen law, according to which the temperature
dependences of the lattice specific heat at constant volume and the linear expansion coefficient are identical to each other,
have been analyzed. The proofs that the specific heat of the quasicrystals contains latent electronic and lattice contributions
of the Schottky type have been obtained. The revealed contributions can be thermodynamic consequences of the fractal energy
spectra. 相似文献
18.
S. E. Bogorodskii L. I. Krotova A. V. Mironov V. K. Popov 《Russian Journal of Physical Chemistry B, Focus on Physics》2013,7(8):916-923
A new method for fabrication of highly porous bioresorbable polymer structures on the basis of various aliphatic polyesters for tissue engineering has been successfully designed and worked out. It has been shown that injection of polymer compositions plasticized in sub- or supercritical carbon dioxide into press forms at temperatures from 20 to 40°C through a nozzle of a certain diameter under atmospheric or elevated (up to 6 MPa) CO2 pressure allows obtaining polymer matrices with a desired structure and morphology and mean porosity of up to 96 vol % with high reproducibility and avoiding the use of toxic organic solvents. The effect of chemical composition and molecular mass of starting polymers, as well as temperature and CO2 pressure in the reaction cell and the receiver, on the morphology and internal structure of fabricated samples was studied using the method of scanning-electron microscopy. 相似文献
19.
Results of heat capacity measurements for LnNi5 compounds with Ln La, Ce, Nd and Gd are presented for the temperature range 5–300°K. Electrical resistivities are given for the Ce, Nd and Gd compounds over the same temperature range. The heat capacities are consistent with the previously observed magnetic behavior of LaNi5, CeNi5 and NdNi5. The La compound is a Pauli paramagnet and its heat capacity behavior is that of a solid exhibiting only vibrational and electronic excitation. CeNi5 remains paramagnetic to 4°K and its Cp behavior closely resembles that of LaNi5. NdNi5 exhibits a A-type thermal anomaly peaking at 6·4°K, which is ascribed to the break-up of ferromagnetism. It also shows excess heat capacity at higher temperatures resulting from excitation in the crystal field spectrum. Results for GdNi5, are unusual. Magnetic entropy is introduced over an anomalously wide range of temperature. The process culminates in two λ-type thermal anomalies peaking at 29·8 and 30·6°K, suggesting that the development of the cooperative phase occurs in two stages. The magnetic transformations are also evident in the resistivity-temperature behavior of NdNi5 and GdNi5, the loss of the spin-disorder resistivity being readily apparent in the former material. The usual thermodynamic properties are computed from the heat capacity data. Magnetic entropies of NdNi5 and GdNi5 at 300°K are observed to be 95 and 86 per cent, respectively, of R In(2J + 1). 相似文献
20.
D. Moses A. Denenstein A. Pron A.J. Heeger A.G. MacDiarmid 《Solid State Communications》1980,36(3):219-224
The temperature dependences (0.8 K ? T < 7 K) of the specific heats of pure polyacetylene (both and isomers) and heavily doped metallic [CH(AsF5)0.12]X are reported. Results for undoped -(CH)X indicate behavior typical of crystalline polymers, whereas isomerization to the -form leads to a small term linear in temperature signifying increased disorder. Comparison of the data from and starting material indicates that isomerization is induced during doping. The increased coefficient of the linear term in the metallic polymer is discussed in terms of two contributions; an electronic term expected for a metal, and the increased effect of disorder in the doped polymer. 相似文献