A new method for the determination of pressure-interatomic separation-temperature relationship is investigated and applied for some alkali halides. The method is developed by using the Mie-Gruneisen equation of state and the Anderson thermal pressure and an ionic model based on Harrison's treatment of overlap repulsive potential which takes into account the interactions up to second neighbors. It is found that the new method yields satisfactory results in agreement with the available experimental data.
Seven hard-sphere models and Flory's statistical mechanical theory have been applied to evaluate thermal expansion coefficient of ternary liquid systems involving dimethyl sulfoxide with phenol/o-cresol in carbon tetrachloride at 293.15, 303.15 and 313.15 K. The results thus obtained are compared with the experimental values of thermal expansivity. The relative applicability of all these approaches to the present investigation has been checked and discussed. The excess values of thermal expansivity have also been calculated and utilized to study the presence and strength of intermolecular interactions in the ternary liquid systems under investigation.
We report the crystal structure evolution of CaCu_{0.2}Mn_{6.8}O_{12} as a function of temperature between 10 K and 290 K. The analysis of the diffraction data is carried out with the Rietveld method applied to the average trigonal structure of CaCu_{0.2}Mn_{6.8}O_{12}. The x = 0.2 member shows similar low temperature extrema for the unit cell parameter evolution as the previously reported x = 0.1 and x = 0 members of the CaCu_xMn_{7-x}O_{12} system. All magnetic and crystallographic transition temperatures indicated by the unit cell parameter evolution obtained by powder X-ray diffraction methods systematically decrease with increasing Cu content, x.
The lattice parameter for polycrystalline diamond is determined as a function of temperature in the 4-300 K temperature range. In the range studied, the lattice parameter, expressed in angstrom units, of the studied sample increases according to the equation a = 3.566810(12) + 6.37(41) × 10^{-14} T^{4} (approximately, from 3.5668 to 3.5673 Å). This increase is larger than that earlier reported for pure single crystals. The observed dependence and the resulting thermal expansion coefficient are discussed on the basis of literature data reported for diamond single crystals and polycrystals.
In this study, using type CEM I 42.5 R Portland cement, limestone powder, polypropylene fibers and super plasticizer, additive foam concrete specimens were produced. 28 days compressive strengths, dry densities, ultrasonic pulse velocities and thermal conductivity coefficient of these samples were determined. Analysing test results, it was noticed that there underlies a strong relationship between ultrasonic pulse velocity and thermal conductivity coefficient in the foam concrete. It is possible to estimate thermal conductivity by ultrasonic pulse velocity method, easy and credible method.
Thermal properties of polypyrrole nanotubes synthesized by the chemical oxidation of pyrrole with iron(III) chloride in the presence of methyl orange as structure-guiding template, have been investigated. As-prepared polypyrrole salt and corresponding base were compressed into pellets. Thermogravimetric analysis has shown that the heating/cooling of both polymers is connected with water desorption/re-absorption. This process influences all temperature dependences of the thermophysical properties. The specific heat of both polypyrrole forms was the same at 35°C. The thermal diffusivity of polypyrrole base was lower than that of the salt. The dilatational characteristics are strongly influenced by water desorption/re-absorption. Water desorption is connected with the contraction of polypyrrole and its re-absorption with the expansion of polypyrrole. The electrical resistivity was measured, in analogy to thermal experiments, by a four-point van der Pauw method. The electrical resistivity was 0.016 and 10.2 Ωcm at room temperature, for both materials. The electrical resistivity was also influenced by water desorption/re-absorption as well as other thermophysical properties.
We have investigated the structural, elastic, electronic, optical and thermal properties of CsBaF₃ perovskite using the full-potential linearized augmented plane wave method within the generalized gradient approximation and the local density approximation. Moreover, the modified Becke-Johnson potential (TB-mBJ) was also applied to improve the electronic band structure calculations. The ground state properties such as lattice parameter, bulk modulus and its pressure derivative were calculated and the results are compared with the available theoretical data. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young's modulus and Poisson's ratio are obtained for the first time. Electronic and bonding properties are discussed from the calculations of band structure, density of states and electron charge density. The contribution of the different bands was analyzed from the total and partial density of states curves. The different interband transitions have been determined from the imaginary part of the dielectric function. The thermal effect on the volume, bulk modulus, heat capacities C_V and the Debye temperature was predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account.
The study of the heat capacity of the intermetallic compound NdNi_{4}Si including the effect of the magnetic field is reported. This compound crystallizes in the hexagonal CaCu_5-type structure, space group P6/mmm. NdNi_{4}Si is ferromagnetic with T_C = 8 K and the saturation magnetic moment of 1.5 μ_{B}/f.u. at 4.2 K (in H = 9 T). The heat capacity was analyzed considering the electronic contribution, the Schottky anomaly, and the lattice contributions in the frames of the Debye model. The scheme of the energy levels created by the crystal electric field split is determined from the Schottky contribution to the specific heat. NdNi_{4}Si was characterized by the electronic heat capacity coefficient γ = 85 mJ/(mol K^2) and the Debye temperature Θp_D = 325 K.
The structural, elastic, thermodynamic and electronic properties of nonmetallic metal FeCrAs are studied within density function perturbation theory. The thermodynamic properties of FeCrAs were deduced based on phonon frequencies within the framework of the quasiharmonic approximation. The calculated elastic modulus under various pressures indicates that FeCrAs is mechanically stable under pressure. The pressure-dependence of bulk and shear modulus, transverse and longitudinal sound velocities V (i.e. V_{S} and V_{L}), elastic Debye temperature Θ_{E} of FeCrAs have also been investigated. The calculated values of B/G indicate that FeCrAs presents high ductility under pressure. However, it is interesting that the value of B/G reaches a maximum under 40 GPa and almost remains unchanged when the pressure is above 70 GPa. The calculations show that the heat capacity C_{V} of this material is close to the Dulong-Petit limit 3R (about 224.61 J mol^{-1} K^{-1}) at high temperature regime. The analysis of electronic properties find that as the pressure increases, the absolute value of charge for As and Fe atom increases while Cr remains nearly a constant, indicating that the mechanic properties of FeCrAs under pressure should be mostly attributed to the interaction between Fe and As atoms.
The structural, elastic anisotropy and thermodynamic properties of the I4mm-B₃C are investigated using first-principles calculations and the quasi-harmonic Debye model. The calculated elastic anisotropic suggest that I4mm-B₃C is elastically anisotropic with its Poisson ratio, shear modulus, the Young modulus, the universal anisotropic index, shear anisotropic factors, and the percentage of elastic anisotropy for bulk modulus and shear modulus. The quasi-harmonic Debye model, using a set of total energy versus molar volume obtained with the first-principles calculations, is applied to the study of the thermal and vibrational effects. The thermal expansions, heat capacities, the Grüneisen parameters and the Debye temperatures dependence on the temperature and pressure are obtained in the whole pressure range from 0 to 90 GPa and temperature range from 0 to 2000 K.
Selected alloys from the Fe-Al system are included into a group of materials on a matrix of intermetallic phases, and characteristic properties result from it and they constitute a resultant between properties of superalloys and ceramic materials. These materials are characterized, inter alia, by capacity for operating at elevated temperatures, as well as good strength related properties and resistance to oxidation and corrosion at an increased temperature. In addition, a low cost of alloy components and low density caused by aluminium content are their advantages. The basic reasons limiting application of alloys from Fe-Al system as construction materials are current: their low plasticity at room temperature, propensity for brittle cracking, low resistance at elevated temperature, and insufficient creep resistance. This unfavorable characteristics may be improved by adding to alloys such elements as molybdenum, zirconium, carbon, and boron, reducing the size of grains, increasing their purity, stabilizing the solid solution, and causing changes in phase transition temperatures. These alloys may be successfully manufactured by classic melting accompanied with refinement remelting, and ingot casting. In spite of additions and microadditions, grain refining of the initial structure of ingots manufactured in that way is rarely achieved, mainly because of low castability and high casting contraction. In this work we presented the results of structure analysis and investigations of the dilatometric study alloys on the base Fe-Al system. The alloys were obtained by classic casting technique. The studies were carried out on samples after casting and annealing. The phase transformation and thermal expansion investigations of the alloys from Fe-Al system with concentration of Fe-58Al were presented. The linear thermal expansion α was calculated by standard method. The α coefficient was noticed as a temperature function.
Lattice parameters for aluminium nitride were determined using X-ray powder diffraction at a synchrotron radiation source (beamline B2, Hasylab/DESY, Hamburg) in the temperature range from 10 K to 291 K. The measurements were carried out using the Debye-Scherrer geometry. The relative change of both, a and c, on rising the temperature in the studied range (10-291 K) is about 0.03%. The results are compared with earlier laboratory data and theoretical predictions.
The structural, elastic anisotropy and thermodynamic properties of the P4̅m2-BC₇ are investigated using first-principles density functional calculations and the quasi-harmonic Debye model. The obtained structural parameters and elastic modulus are in consistency with the available theoretical data. Elastic constants calculations show that P4̅m2-BC₇ is elastic anisotropic. The bulk modulus as well as other thermodynamic quantities of P4̅m2-BC₇ (including the Grüneisen constant, heat capacity and thermal expansion) on temperatures and pressures have also been obtained.
The present study of Ni_{2}MnGe is focused on describing the thermal properties of the alloy in the framework of first-principles electronic structure calculations coupled with a Debye treatment of the vibrating lattice. The electronic structure of Ni_{2}MnGe has been studied using the full-potential nonorthogonal local-orbital minimum basis method. Two approximations for Grüneisen parameter γ, i.e. Slater's and Dugdale and MacDonald's expressions were assumed.
Longitudinal and shear ultrasonic wave velocities were measured in binary Li_2O-2B_2O_3 glasses doped with different transition metal oxides (TMOs) (where TMO = V_2O_5, Fe_2O_3, Cr_2O_3, NiO, TiO_2, MnO_2 and CuO) using pulse echo technique. Measurements were carried out at 4 MHz frequency and at room temperature. Elastic moduli and some other physical parameters such as acoustic impedance, Debye temperature, thermal expansion coefficient, and latent heat of melting were calculated. Results indicated that these parameters depend upon the TMO modifier i.e., the ionic radius of the transition metal cation. Quantitative analysis has been carried out, in order to obtain more information about the structure of these glasses, based on bond compression model, and the Makishima and Mackenzie model, i.e., the cation-anion bond of each TMO.
Crystal structure and transport properties of the mixed praseodymium cobaltites-ferrites PrCo_{1-x}Fe_xO₃ have been studied in the temperature range of 298-1173 K by a combination of in situ X-ray synchrotron powder diffraction and temperature dependent impedance spectroscopy measurements. In situ high temperature powder diffraction examination of PrCo_{1-x}Fe_xO₃ series revealed considerable anomalies in the lattice expansion which are especially pronounced for the cobalt-rich specimens. These anomalies, which are reflected in a sigmoidal dependence of the unit cell dimensions and in the considerable increase of the thermal expansion coefficients, are obviously associated with transitions of Co^{3+} ions from low spin to the higher spin states and the coupled metal-insulator transitions, occurring in in rare earth cobaltites at the elevated temperatures. Indeed, the temperature-dependent impedance measurements clearly prove the change of conductivity type from dielectric to the metallic behaviour in the mixed cobaltite-ferrites PrCo_{1-x}Fe_xO₃ at the elevated temperatures.
In this paper, a new isothermal equation of state is developed based on an approximation for the volume dependence of the Anderson-Grüneisen parameter δ_T along isotherm. The values of interatomic separation r with the change of pressure for nine alkali halides and periclase were investigated with the help of the new isotherm equation of state. The compression data are used to predict the pressure dependence of the coefficient of volume thermal expansion. The results are compared with the available experimental data and other theoretical results.
We measured the lattice constants of bulk aluminum nitride crystals at various temperatures by high resolution X-ray diffraction. By the use of a high temperature chamber and a X-ray cryostat a temperature regime from 20 to 1210 K was available. Furthermore, the measured data were fitted by Einstein- and Debye models which yield reliable parameters for the calculation of the thermal expansion coefficients of AlN.
We investigated the lattice dynamics of the prototypic ferroelectric barium titanate close to its ferroelectric-paraelectric phase transition aiming at a better understanding of the atomistic nature of the transition. The usage of time-resolved X-ray techniques allows to disentangle lattice motion and unit cell changes, which, in part, relate to the ferroelectric polarization. In the quasi-static case both the electrical and the laser excitation show a mean-field, simple thermal behaviour, while for time scales shorter than nanoseconds the impulsive nature of the excitation becomes visible.
Crystal structures of two yttrium aluminium oxides, namely YAlO_3 and Y_3Al_5O_{12}, were investigated in the temperature range 3.4-300 K by high-resolution neutron powder diffraction. Neither traces of phase transformations nor discontinuous changes of physical properties were observed. Thermal expansion of yttrium aluminium oxides was evaluated in terms of 1st order Grüneisen approximation, where the Debye temperatures and the Grüneisen parameters have been estimated for both compositions. Anomalies in the thermal expansion of yttrium aluminium perovskite have been observed and modelled using the Einstein oscillator with negative Grüneisen parameter. Extended bond length analysis revealed significant thermally-driven modifications of the aluminium-oxygen framework.
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