Temperature Dependence Of Thermodynamic Properties Research Articles

Effect of hydrostatic compression on physical properties of Li2TmSi3 (Tm = Ir, Pt, Rh, Os) with ground-state optical features

Using density functional theory (DFT) the first-principles calculations are employed to systematically investigate the effect of hydrostatic compression on the structural, elastic, electronic, thermal and thermodynamic properties of ternary silicides Li2TmSi3 (Tm = Ir, Pt, Rh, Os) with the ground-state optical features. The gradual decrease of bond length, unit cell volume and a smooth change of c/a with pressure deny the possibility of pressure induced phase transition up to 50 GPa. All the compounds studied here are mechanically stable within the considered pressure range. The constants C11, C12, C13 and C33 exhibit an almost linear increase trend with increase of pressure, while C44 shows anomalous behavior. The bond-stretching and bond-bending force constants are calculated based on the data of elastic constants and their pressure dependent behavior are discussed. Hydrostatic pressure enhances the inherent elastic anisotropy of Li2TmSi3. The ternary silicides studied here cannot be easily compressed under uniaxial stress. The atomic bonds between the nearest neighbors along [001] direction are stronger than those along [100] direction in the whole range of pressure. All ternary silicides except Li2PtSi3 are brittle in nature at ambient pressure. Under elevated pressure all studied compounds show brittle to ductile transition except Li2PtSi3 that exhibits brittle nature under 10 GPa. The shear modulus of Li2OsSi3 shows anomalous change under pressure, which may be attributed from its anomalous change of θD. The higher melting point of all silicides implies that they might have possible uses in harsh environments. The TDOS at EF in Li2TmSi3 decreases almost linearly with pressure. Pressure and temperature dependent thermodynamic properties and ground-state optical functions are described with implications, which may be supportive for further investigation of these compounds through experiments and theories.

First-Principles Study of Mechanical and Thermodynamic Properties of Binary and Ternary CoX (X = W and Mo) Intermetallic Compounds.

In this study, the structural, elastic, and thermodynamic properties of DO19 and L12 structured Co3X (X = W, Mo or both W and Mo) and μ structured Co7X6 were investigated using the density functional theory implemented in the pseudo-potential plane wave. The obtained lattice constants were observed to be in good agreement with the available experimental data. With respect to the calculated mechanical properties and Poisson’s ratio, the DO19-Co3X, L12-Co3X, and μ-Co7X6 compounds were noted to be mechanically stable and possessed an optimal ductile behavior; however, L12-Co3X exhibited higher strength and brittleness than DO19-Co3X. Moreover, the quasi-harmonic Debye–Grüneisen approach was confirmed to be valid in describing the temperature-dependent thermodynamic properties of the Co3X and Co7X6 compounds, including heat capacity, vibrational entropy, and Gibbs free energy. Based on the calculated Gibbs free energy of DO19-Co3X and L12-Co7X6, the phase transformation temperatures for DO19-Co3X to L12-Co7X6 were determined and obtained values were noted to match well with the experiment results.

Information processing and thermodynamic properties of microtubules

The Shannon entropy dependence on temperature, dipole moment and thermodynamic properties of microtubules (MTs) have been investigated using the Landau–Ginzburg phenomenological theory through continuum Boltzmann distribution function. By minimising the loss in energy, we found that there is a possibility that MTs formed from the heterodimers can process information over a long time at higher temperature. We also found that multiple heterodimers under the influence of dipole moment, has the tendency to process information whenever the amount of information stored or transferred decreases with increasing electronegativity of the system. We analyse the dynamic instability phenomenon that infinitely occurs in polymerisation and depolymerisation processes in MTs. Also, under physiological conditions, temperature dependence of thermodynamic properties was investigated and our results exhibited critical behaviour of heat capacity and chemical potential giving room for phase transitions around 302 K.

An efficient approximation of the supercell approach to the calculation of the full phonon spectrum

The supercell approach to first-principles calculations of an alloy's full phonon spectrum is computationally expensive. It is therefore rarely used for calculating temperature dependent free energies of alloy phases or for calculating alloy phase diagrams. Amid the wider acceptance of uncertainty evaluation and the use of more efficient methods for materials design, the supercell approach is revisited and a simpler and more computationally efficient approximation is proposed. The new method is then used to calculate the Cr-Ni temperature dependent thermodynamic properties and phase diagram, resulting in predictions that are in good agreement with previous thermodynamic assessment. The new approach can facilitate accurate and rapid CALPHAD thermodynamic assessments of multi-component systems.

Quantum mechanical computation, spectroscopic exploration and molecular docking analysis of 2-Bromo-4-fluoroacetanilide

The optimized structural parameters and vibrational frequencies of the elemental modes of 2-Bromo-4-fluoroacetanilide are obtained using density functional theory (DFT) technique within the B3LYP approximation and 6–311++G (d, p) basis set. The elaborated vibrational assignments of the ascertained FT-IR and FT-Raman bands were projected on the premise of P.E distribution (PED). Most of the modes have wavenumbers are within the expected range. The primary static hyperpolarizability, MEP and therefore the contour map of the molecule were mapped as a primarily for predicting sites and relative reactivity towards electrophilic and nucleophilic attack. The steadiness of the molecule arising from the hyper conjugative interaction and charge delocalization were scrutinized with NBO. HOMO-LUMO energy calculations have exposed the charge transfer within the molecule. Absorption wavelengths and their assignments in UV–vis region were forecasted by based on time-dependent density functional theory (TD-DFT) calculations. The temperature dependence of thermodynamic properties were analyzed. Associate with a symptomatic antidiabetic activity of the title compound were confirmed from the molecular docking.

Gas-to-Liquid Phase Transition of PAH at Flame Temperatures.

Significant evidence has shown that soot can be formed from polycyclic aromatic hydrocarbon (PAH) in combustion environments, but the transition of high molecular PAH from the gas phase to soot in a liquid or solid state remains unclear. In this study, the relationships between the boiling points of various planar PAHs and their thermodynamic properties are systematically investigated, to find a satisfactory marker for the phase transition event. Temperature-dependent thermodynamic properties, including entropy, specific heat capacity, enthalpy, and Gibbs free energy, are simultaneously calculated for PAHs, using density functional theory and three composite compound methods. Comparison of the results indicates that the individual G3 method, plus an atomization reaction approach, produces the most accurate thermochemistry parameters. Compared to entropy, enthalpy, and Gibbs free energy, the specific heat capacity at 298 K is found to be a better marker for the boiling point of PAHs due to the observed linear correlation, predictable characteristics, and fidelity of accuracy as a function of temperature. The correlation equation Y = 10.996X + 122.111 is proposed (where Y is the boiling temperature (K) and X is Cp at 298 K (cal/K/mol)). The standard deviation is as low as 16.7 K when comparing the calculated boiling points and experimentally determined values for 25 different aromatic species ranging from benzene to ovalene (C32H14). The effects of carbon number, structural arrangement, and partial pressure on the boiling point of large planar PAH are discussed. The results reveal that the carbon number in large planar PAH is the dominant factor determining its boiling points. It is shown that PAHs containing about 60-65 carbon atoms are likely to exist as liquids in flames, although the partial pressure of such species is very low.

Temperature-induced structural change through the glass transition of silicate glass by neutron diffraction

Supercooled silicate liquids exhibit several orders of magnitude increase in viscosity at the glass-transition temperature (${T}_{\mathrm{g}}$) towards the glassy state. Such a drastic dynamical slowdown leads to an abrupt change in the slope of temperature-dependent thermodynamic properties because the measurements reflect the equilibrium-to-nonequilibrium change from liquid to glass. However, an underlying structural change associated with such a transition remains elusive. For instance, understanding the structural origin of the variation in the coefficient of thermal expansion (CTE) of silicate glasses upon vitrification is critical for glass-manufacturing processes and applications. Here, based on temperature-dependent neutron diffraction, we demonstrate that the temperature dependences of both short- and medium-range order structural parameters show a pronounced change of slope at ${T}_{\mathrm{g}}$ for a range of silicate glasses of industrial importance. Interestingly, the short- and medium-range order structural parameters are found to be mutually correlated, both below and above ${T}_{\mathrm{g}}$. Based on these results, we find that the slope change of the area of the first sharp diffraction peak at ${T}_{\mathrm{g}}$ is correlated with the extent of the CTE jump at ${T}_{\mathrm{g}}$, which offers a structural origin for the discontinuity in the CTE of glasses at ${T}_{\mathrm{g}}$. This study can therefore shine light on solving critical industrial problems, such as glass relaxation.

First Principles Investigation on Thermodynamic Properties and Stacking Fault Energy of Paramagnetic Nickel at High Temperatures

Reliable data on the temperature dependence of thermodynamic properties of alloy phases are very useful for modeling the behavior of high-temperature materials such as nickel-based superalloys. Moreover, for predicting the mechanical properties of such alloys, additional information on the energy of lattice defects (e.g., stacking faults) at high temperatures is highly desirable, but difficult to obtain experimentally. In this study, we use first-principles calculations, in conjunction with a quasi-harmonic Debye model, to evaluate the Helmholtz free energy of paramagnetic nickel as a function of temperature and volume, taking into account the electronic, magnetic, and vibrational contributions. The thermodynamic properties of Ni, such as the equilibrium lattice parameter and elastic moduli, are derived from the free energy in the temperature range from 800 to 1600 K and compared with available experimental data. The derived temperature dependence of the lattice parameter is then used for calculating the energies of intrinsic and extrinsic stacking faults in paramagnetic Ni. The stacking fault energies have been evaluated according to three different methodologies, the axial-next-nearest-neighbor Ising (ANNNI) model, the tilted supercell approach, and the slab supercell approach. The results show that the elastic moduli and stacking fault energies of Ni decrease with increasing temperature. This “softening” effect of temperature on the mechanical properties of nickel is mainly due to thermal expansion, and partly due to magnetic free energy contribution.

A first principle study of the structural, electronic, and temperature-dependent thermodynamic properties of graphene/MoS2 heterostructure.

After an initial assessment of the structural and electronic properties of graphene, monolayer MoS2, and graphene/MoS2 bilayer hetero-structure, the temperature-dependent thermodynamic properties of graphene/MoS2 bilayer hetero-structure are examined by using density functional theory calculations. The structure, bandgap, partial density of states, and thermodynamic properties of graphene, monolayer MoS2 and graphene/MoS2 system are investigated and analyzed. Findings from the present study are in good agreement with the previously reported theoretical and experimental studies. Monolayer MoS2 and graphene form a stable Van der Waals heterostructure owing to their negative binding energy, and the system acts as a zero-bandgap semiconductor. Debye temperature and the heat capacity of graphene, MoS2 monolayer, and graphene/MoS2 system are calculated from phonon dispersion relations to be 2100K, 600K, and 1400K, and 0.7J/g.K, 0.218J/g.K, and 0.46J/g.K, respectively. Introduction of graphene into the MoS2 semiconductor is, therefore, found to improve the overall thermodynamic properties of the composite as graphene preserved its superior thermal properties. The findings will be beneficial to calculate thermal conductivity of the graphene/MoS2 heterostructure for minimizing the temperature effect in electronic or optoelectronic devices.

Comprehensive first-principles calculations on physical properties of ScV2Ga4 and ZrV2Ga4 in comparison with superconducting HfV2Ga4

We use first-principles method for a comprehensive investigation of structural, elastic, electronic, Mulliken atomic population based bonding, phonon, thermodynamic and optical properties of ScV2Ga4 and ZrV2Ga4 in comparison with the isostructural HfV2Ga4 superconductor. The single and polycrystalline elastic constants are all evaluated and discussed. Cell stability employing elastic constants criteria, formation enthalpy and phonon dispersion are verified. Brittleness and hardness features are also discussed. Elastic anisotropies are evaluated and discussed to unravel some of the macroscopic behaviors of the studied compounds. The significant overlapping between conduction and valence bands in the vicinity of Fermi level (EF) confirms the metallic characteristics for MV2Ga4 (M = Hf, Sc, Zr). It is predicted that the TDOS around the EF arises mostly from V–3d with a smaller contribution of Ga–4p states. The Fermi surfaces show multiband nature but that of ScV2Ga4 has different and complex shape in contrast to ZrV2Ga4 and superconducting HfV2Ga4. The bonding characteristics are analyzed using the energy band structure, charge density distribution and Mulliken atomic and bond overlap population. Such analysis exhibits directional electronic density-channel, highly populated 1D V leashed in (100) plane in the lattices. The formation of such V-chains which accumulate the highest electronic charge might generate Cooper pairs to exhibit superconducting behavior in the yet unobserved Sc and Zr containing compounds. The phonon dispersion curves, phonon density of states and optical phonon frequencies, Raman and infrared activities of the materials are discussed for the first time. The temperature dependent thermodynamic properties including heat capacity at constant pressure are calculated as a function of temperature and compared with the available data. Various optical properties are calculated and their features are analyzed. The potentials of the compounds for practical uses as coating materials to reduce solar heating and enhance radiative cooling are also mentioned.

Pressure and temperature effect of hexagonal phase FeN2: A first-principle study

Abstract The elastic, hardness, anisotropy and thermodynamic properties of h-FeN2 under pressure have been systematically investigated via the first-principles calculations. The predicted lattice constants are well consistent with the existing experimental data and the previous theoretical results. The elastic constants, polycrystalline modulus, anisotropy and hardness of h-FeN2 under pressure have been calculated. According to the obtained results, h-FeN2 is mechanically stable, possesses elastic anisotropy and high hardness, and can be classified as brittle material. In addition, the pressure and temperature dependent thermodynamic properties including the Debye temperature and isochoric heat capacity C v are also reported and discussed using the quasi-harmonic approximation (QHA). So far as we know, this is the first time quantitative study of the effects of temperature and pressure on the thermodynamic and mechanical properties of h-FeN2. Our theoretical researches still waits for experimental confirmation.

Structural and thermodynamic properties of cubic sphalerite aluminum nitride under hydrostatic compression

The present work aims to investigate the structural phase stability and thermodynamic properties of aluminium nitride with cubic zinc-blende structure at normal and high pressures (up to 5 GPa) and high temperatures (up to 2000 K). In this study, we use the pseudopotential plane wave method within the framework of the density functional theory with the local density approximation for the exchange-correlation functional. The phase transition pressure has been determined and found to be in very good agreement with several theoretical data. The pressure and temperature dependences of thermodynamic properties are successfully presented, analyzed and discussed in details. Besides, the plasmon energy and microhardness are examined.

Molecular dynamics simulations of the thermodynamic properties and local structures on molten alkali carbonate Na2CO3

Molten carbonate salts as phase change materials have received particular attention for high-temperature thermal energy storage and heat transfer applications due to desirable thermal characteristics such as wide operating temperature range, low causticity and excellent thermal stability. In this study, molecular dynamics (MD) simulations were performed on molten alkali carbonate Na2CO3 based on an effective pair potential model, a Born-Mayer type combined with a Coulomb term. The temperature dependences of thermodynamic properties including the density, thermal expansion coefficient, specific heat capacity, shear viscosity, thermal conductivity and ion self-diffusion coefficient were simulated in detail from 1150 to 1500 K, which was all difficult to achieve from experiments on account of high-temperature extreme conditions. The simulation results were in satisfactory agreement with experimental data available with high calculation accuracies. In particular, both the equilibrium molecular dynamics (EMD) and non-equilibrium molecular dynamics (NEMD) simulations were tried to calculate the shear viscosity and thermal conductivity, and the NEMD method turned out to be more suitable for molten alkali carbonate salts with higher calculation accuracies of 15.11% and 22.48% for shear viscosity and thermal conductivity separately. Moreover, the radial distribution functions (RDF) and coordination number curves of the molten salt were characterized to explore the temperature dependences of macroscopic properties from microscopic view, and the results suggested that the changes of thermodynamic properties with temperature were induced by the distance changes between Na2CO3 particles. Besides, it could be concluded that the structure of CO32− was inferred reasonably to be ortho-triangular pyramid from the comprehensive analysis of local structures including the angular distribution functions (ADF).

Temperature dependence of thermodynamic properties of MoS2 monolayer and single-wall nanotubes: Application of the developed three-body force field

MoS2 nanostructures, especially mono-, multilayer nanothin films as well as single- and multiwall nanotubes are rather interesting popular objects in nanomaterials chemistry. The thermodynamic properties of inorganic nanotubes, and the temperature dependence of their properties can be efficiently investigated by first-principles and molecular mechanics methods in the framework of harmonic approximation. At the same time, only thin single-wall nanotubes are available for the first-principles calculations. The classical mechanics is suitable to simulate very large atomic systems and their phonon frequencies, but developing sufficiently accurate force field is rather tedious work. Herein, we report the force field fitted to the experimental and first-principles data on the structure of 2H- and 3RMoS2 polytypes of bulk crystal, structure of monolayer and several bilayers, vibrational frequencies of 2HMoS2 bulk and monolayer, relative energetic stability of polytypes experimental and first-principles data, elastic constants, strain energy of a (12, 12) MoS2 nanotube. The thermodynamic functions and their temperature dependence for the armchair and zigzag nanotubes are calculated within the formalism of molecular mechanics using elaborated interatomic potential. The results of molecular mechanics and first-principles method application to the thinnest nanotubes are compared.

High-temperature mechanical and thermodynamic properties of silicon carbide polytypes

Silicon carbide is widely used as ultra high-temperature ceramics, semiconductors, and pressure sensors with promising potentials for high-temperature, high-endurance, and radiation hardened applications. Daunting difficulties in experimental investigations of thermophysical properties hinder the better understanding of high-temperature material behaviors of silicon carbide. We present a comprehensive study of temperature-dependent mechanical and thermodynamic properties of SiC polytypes by first-principles methods. The obvious anisotropy of linear expansion and elasticity is found for 3C-SiC, while it is not distinct for other non-cubic SiC polytypes. Results show that the temperature dependences of mechanical properties exhibit the softening behavior, in which small linear reduction (∼4.4%) in Vickers hardness and shear modulus but large linear reduction (∼7.0%) in Young's modulus are detected. The heat-resistant properties of SiC polytypes are ranked as 3C-SiC < 4H-SiC < 6H-SiC < 15R-SiC < 2H-SiC. The present predictions are in favorable accord with available measured data in the literature.

Investigation of the mechanical and thermodynamic properties of the U3Pt4 and Th3Pt4

The elastic, Vickers hardness and anisotropy properties of A3Pt4 (A = U and Th) have been extensively investigated by the first principles calculations. The obtained equilibrium lattice parameters are in good agreement with the available experimental data. The calculated elastic constants meet the mechanical stability conditions, demonstrating that A3Pt4 are mechanically stable. The bulk modulus, Young's modulus, shear modulus and hardness of A3Pt4 were calculated. The results reveal that both of them are ductile, and the hardness is 0.26 GPa and 2.7 GPa for U3Pt4 and Th3Pt4, respectively. The elastic anisotropy was characterized by several different methods. The results demonstrate that the anisotropy of U3Pt4 is more prominent than Th3Pt4. Furthermore, through the quasi-harmonic Debye (QHD) model, the temperature dependence of thermodynamic properties of A3Pt4 has been obtained. Our theoretical calculations suggest that the Cv and Cp of A3Pt4 are increase with increasing temperature, and the Cv is about 173.07 J/mol.K and 170.65 J/mol.K at 300 K, respectively. The Cp of A3Pt4 are good agreement with the available experimental data in the low temperature region. Finally, the Debye temperature θD and the minimum thermal conductivity Kmin were obtained, and further analyses show that A3Pt4 are potential thermal insulating materials.

Effect of anti-site point defects on the mechanical and thermodynamic properties of MgZn2, MgCu2 Laves phases: A first-principle study

A theoretical investigation on the effect of anti-site point defects on mechanical and thermodynamic properties of MgZn2 and MgCu2 based on the first-principles calculations has been implemented. The results show that Mg anti-site defect on Zn or Cu site plays a reinforcing role, while exhibiting a more brittle behavior. However, the defect phase of Cu anti-sites on Mg sublattice shows a ductile tendency. The temperature-dependent thermodynamic properties are also predicted along with Debye-Grüneisen model including Debye temperature, thermal expansion coefficient and vibrational heat capacity as well as vibrational entropy. Taking into account the contribution of the lattice vibration and thermal electronic excitations, the Helmholtz free energy F can be calculated, suggests that anti-site defects caused by the occupancy of Mg at the Zn or Cu site are thermodynamically unstable compared to the defect-free phases. In addition, the total amount of charge transfer, the overall and the local difference charge densities are further discussed to analyze the mechanism of mechanical properties.

Theoretical investigations on temperature dependence of thermodynamic properties and concentration fluctuations of In-Tl binary liquid alloys by optimization method

The thermodynamic properties, i.e. free energy of mixing (GM), heat of mixing (HM), entropy of mixing (SM) and activity (ai) of the component i (i , and structural property i.e. concentration fluctuations in long wave-length limit [Scc(0)] of In-Tl binary liquid alloy at a specified temperature have been investigated in the framework of quasi-lattice model on assuming the coupled effect of size ratio and entropic (or energetic) as well as enthalpic effect. These properties of In-Tl liquid alloy at 723 K have been computed theoretically by estimating the best fit value of order energy parameter (W) and size ratio () over the entire range of concentration in order to match their experimental values. The best fit value of W at 723 K has been used to determine the values of W at different temperatures with the help of temperature derivative of W which are then used for the optimization procedure in order to calculate the corresponding values of excess free energy of mixing, partial excess free energy of mixing and activity of the components involved in the alloy at different temperatures. These parameters have been used to investigate the concentration fluctuations in long wavelength limit {Scc(0)} of In-Tl binary liquid alloy at different temperatures over the entire range of concentration which have been used to predict the various other structural properties like excess stability function (EXS), diffusion coefficient ratio (Dm/Did), short range order parameter (α1) at different temperatures.BIBECHANA 15 (2018) 11-23

High-Pressure and Temperature Dependence of Electronic, Magnetic, Elastic, Thermodynamic, and Transport Properties of Full-Heusler Alloys Co2YIn (Y = Nb, Zr)

Structural, elastic, magnetic, and electronic properties of Co2YIn (Y = Nb, Zr) have been investigated by means of the full-potential linearized augmented plane wave along with generalized gradient approximation + U/modified Becke-Johnson method in the stable Fm-3m phase. The optimized equilibrium lattice parameter in stable phase is 6.1744 A for Co2NbIn and 6.2824 A for Co2ZrIn. We have calculated the spin-resolved density of states for both the alloys to show that the ferromagnetic behavior of Co2NbIn is due to the exchange splitting of Co and Nb atoms and due to Co and Zr in Co2ZrIn. In spin-up configuration, there is absence of energy gap while an energy gap can be seen in spin-down state for both the alloys exhibiting a half-metallic character. Through the elastic constants and their discussions, we have predicted the elastic behavior of the materials. The quasi-harmonic approximations have been employed to study the pressure- and temperature-dependent thermodynamic properties. The Boltzmann theory is employed to investigate the electronic transport properties of these alloys. The defined material properties may pay as a prime stand for the application of material in spintronics and thermoelectrics.

Molecular dynamics simulations on the binary eutectic system Na2CO3-K2CO3

Molten carbonate salts as phase change materials have received particular attention for high-temperature thermal energy storage and heat transfer applications due to desirable thermal characteristics such as wide operating temperature range, low causticity and excellent thermal stability. In this study, molecular dynamics (MD) simulations were performed on the binary carbonate salt Na2CO3-K2CO3 (58-42 mol%) based on an effective pair potential model, a Born-Mayer type combined with a Coulomb term. The temperature dependences of thermodynamic properties including the density, sheer viscosity and thermal conductivity were simulated in detail from 1000 to 1400 K, which were all difficult to achieve from experiments on account of high-temperature extreme conditions. Moreover, the radial distribution functions (RDF) and coordination number curves of the binary carbonate salt were characterized to explore the mechanisms of their temperature dependences from microscopic view. The simulation results suggested that the changes of thermodynamic properties with temperature were induced by the distance changes between ions. Besides, it can be concluded that the high bond energy in the strong covalent bond C-O of molten carbonate salts must contribute to the large specific heat capacity in comparison with that of molten un-oxyacid salts.