Temperature Dependence Of Heat Capacity Research Articles

Evaluating the properties of the intermetallic compound HoN for magnetic refrigerator application: Combined DFT and Monte Carlo simulation

Evaluating the properties of the magnetocaloric material regenerators is a crucial step in order to exploit them subsequently as the working substances in magnetic cooling devices. So, the main objective of this latter is to evaluate the electronic, magnetic properties as well as the magnetocaloric effect of HoN compound. To do so, a combination of DFT study and Monte Carlo simulations has been performed on HoN compound which undergoes a second-order ferromagnetic-paramagnetic phase transition. For this material, the temperature-dependent total magnetization, heat capacity and magnetic susceptibility have been calculated and are revealed that the curie temperature is acceptable concurrence with the experimental value. Furthermore, it was showed that under an applied magnetic field of 5T, the magnetocaloric effect (MCE) in regard to the maximum value of magnetic entropy change ΔSmagmax around its Curie temperature, agree well with the experimental one. Besides, the relative cooling power (RCP) values are found to be 28.5, 162.2 and 227 J. Kg−1 under different magnetic fields of 1,3 and 5T. All findings which are presented in the present work indicate that the large values of RCP and ΔSmagmax found in HoN are interesting for low-temperature magnetic refrigeration with excellent performance.

Using Hyperoptimized Tensor Networks and First-Principles Electronic Structure to Simulate the Experimental Properties of the Giant {Mn84} Torus.

The single-molecule magnet {Mn84} is a challenge to theory because of its high nuclearity. We directly compute two experimentally accessible observables, the field-dependent magnetization up to 75 T and the temperature-dependent heat capacity, using parameter-free theory. In particular, we use first-principles calculations to derive short- and long-range exchange interactions and compute the exact partition function of the resulting classical Potts and Ising spin models for all 84 Mn S = 2 spins to obtain observables. The latter computation is made possible by using hyperoptimized tensor network contractions, a technique developed to simulate quantum supremacy circuits. We also synthesize the magnet and measure its heat capacity and magnetization, observing qualitative agreement between theory and experiment and identifying an unusual bump in the heat capacity and a plateau in the magnetization. Our work also identifies some limitations of current theoretical modeling in large magnets, such as sensitivity to small, long-range exchange couplings.

Thermodynamics of globular protein native structure

The temperature dependence of the partial heat capacity of the native protein structure in an aqueous solution has been analyzed. It is shown that the strictly linear temperature dependence is due to the contributions of the vibrational and conformational components, which indicates volume consistensy and the absence of conformational transitions up to the main two-state transition. The two-level structural and functional organization of the protein three-dimensional structure are considered in relation to the energy and conformational entropy properties in accordance with the principles of the organization of the protein macromolecule. Communicated by Ramaswamy H. Sarma

La2Pd2In: superconductivity and lattice properties at ambient and elevated pressures

Lattice and electronic properties of La2Pd2In were studied at ambient and elevated pressures so as to determine features related to a specific atomic coordination without any influence of magnetism. We describe temperature dependences of lattice parameters, heat capacity and electrical resistivity of single-crystalline La2Pd2In (s.g. P4/mbm) in a broad temperature range 0.09–300 K. Together with the anisotropic effect of hydrostatic pressure, showing that the lattice is more compressible in the basal plane, we can conclude that the lattice is affected by degrees of freedom of the La atoms with positions not imposed by symmetry. The lattice anisotropy is smaller than that found for isostructural ferromagnet Ce2Pd2In. The equilibrium bulk modulus B 0 = (48 ± 3) GPa was determined on the basis of individual linear compressibilities. Measurement of electrical resistivity indicated a superconducting state below T = 0.59 K with a low critical field 0.005 T at T = 380 mK. The onset of superconducting state as a bulk property of La2Pd2In was confirmed by measurements of specific heat and AC magnetic susceptibility. Experimental data can be accounted by first-principles electronic-structure calculations based on density-functional theory. The measured Sommerfeld coefficient γ = 10.6 mJ mol−1 K−2, only marginally exceeding the calculated γ = 9.34 mJ mol−1 K−2, indicates only weak electronic correlations.

Development and application of a uranium mononitride (UN) potential: Thermomechanical properties and Xe diffusion

Atomic-scale modeling of thermophysical and defect properties of uranium mononitride (UN) plays an important role in establishing a better understanding and improved models of UN fuel performance. Having an accurate interatomic potential is crucial for generating reliable data at finite temperatures using molecular dynamic simulations. We report a new interatomic potential for UN, based on a combination of many-body and pairwise interactions, a simple form that we later show could be easily adapted to include Xe–U and Xe–N interactions, i.e., generating a U–N–Xe interatomic potential. The potential was fitted to experimental thermal expansion and single crystal elastic constants, as well as Frenkel, Schottky, anti-Schottky, and antisite pair reaction energies from density functional theory (DFT) calculations. Using the potential, we successfully reproduced experimental lattice parameters, thermal expansion, single crystal elastic constants, and temperature dependent heat capacity. The potential also performs reasonably well in reproducing the energy of the aforementioned stoichiometric defect reactions and defect migration barriers calculated using DFT. However, the potential underestimates the energy difference between the tetrahedral and dumbbell uranium interstitials, and a more complex potential form might be needed to overcome this issue. The potential was also used to predict UN single crystal elastic constants and elastic properties at different temperatures, showing that UN becomes softer and more compressible with increasing temperature. We also compare our potential against literature data from previous empirical potentials, demonstrating similar or better behavior depending on the property of interest. To enable the simulation of Xe in UN a Buckingham potential has been fitted to DFT-derived Xe incorporation energies. The potential was then used to determine the activation energy for Xe diffusion due to various Xe-containing defects, with {XeU:VU} exhibiting the lowest activation energy.

Magnetic phase transitions in the LiNi0.9 M 0.1PO4 (M = Mn, Co) single crystals

The LiNiPO4, LiNi0.9Mn0.1PO4, and LiNi0.9Co0.1PO4 single crystals are studied with heat capacity and neutron diffraction measurements over the temperature interval (10–30) K. Two peaks are observed on the temperature dependence of heat capacity for LiNiPO4, and LiNi0.9Co0.1PO4 samples. One peak indicates the first order phase transition from an antiferromagnetic commensurate (C) structure to an incommensurate (IC) one upon heating. According to neutron diffraction, in LiNiPO4 the IC ordering is described by the propagation vector k = 2π/b(0, 0.080, 0) at the Néel temperature T N = 20.8 K, and k = 2π/b(0, 0.098, 0) at T N = 20.2(1) K for LiNi0.9Co0.1PO4. A further increase in temperature leads to the second order phase transition to a paramagnetic state at critical temperature T IC = 21.7 K and 21.1 K for LiNiPO4 and LiNi0.9Co0.1PO4, respectively. The C and IC phases coexist over the temperature interval (20.6–20.8) K and (20.2–21.2) K in LiNiPO4 and LiNi0.9Co0.1PO4, respectively. In the LiNi0.9Mn0.1PO4 the magnetic phase transition occurs at T N = 22.7 K, but a magnetic scattering is observed up to 24.6 K.

CaMoO-=SUB=-4-=/SUB=--NaGd(MoO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=- Solid Solutions: simulation of properties and local structure by the method of interatomic potentials

Simulation of CaMoO4-NaGd(MoO4)2 solid solutions by the method of interatomic potentials is carried out. It is shown that solid solutions exist in the entire range of compositions and are close to ideal. Dependences on the composition of the lattice parameters and volume of the unit cell, density, bulk modulus, enthalpy, vibrational entropy and heat capacity are obtained. Temperature dependences of heat capacity and vibrational entropy are constructed. Analysis of the local structure and its changes depending on the composition of the Ca1-xNax/2Gdx/2MoO4 solid solution showed that in solid solution the interatomic distances of Gd-O are on average 2.62% less, and Na-O is 3.15% greater than the distances of Ca-O. In general, this leads to an increase in the lattice parameters and volume of the unit cell during the formation of Ca1-xNax/2Gdx/2MoO4 solid solutions compared to CaMoO4. Keywords: simulation, molybdates, the solid solutions, local structure.

First principles study of the structural, electronic, optical and thermal properties of chalcopyrite semiconductor LiAlTe-=SUB=-2-=/SUB=-

The structural, electronic, optical and thermal properties of chalcopyrite LiAlTe2 are studied using the full potential linearized augmented plane wave (FP-LAPW) method framed within density functional theory (DFT). The Wu-Cohen generalized gradient approximation (WC-GGA) was used as exchange-correlation potential to calculate the structural properties. Furthermore, the Tran and Blaha modified Becke-Johnson (mBJ) functional was also employed to compute the electronic and optical properties in order to get best values. The structural parameters at equilibrium are in good agreement with previous experimental and theoretical calculations. The band structures and density of states are calculated and it is found that LiAlTe2 compound is a direct band gap (-) semiconductor. In addition, the optical properties such as dielectric function, refractive index, reflectivity and absorption coefficient are calculated for photon energies up to 25 eV. This study on the optical properties has also been enriched by the introduction of the analysis of birefringence and anisotropy for this material. The calculated values of all parameters are compared with the available theoretical data where a reasonable agreement has been obtained. The study of the material properties at high temperatures and pressures is very important to understand the behavior of a material in severe conditions, so the temperature and pressure dependencies of unit cell volume, bulk modulus, Debye temperature and specific heat capacities are obtained at different temperatures (0-1000 K) and pressures (0-8 GPa) using the quasi-harmonic Debye model. To our knowledge this is the first theoretical prediction of the thermal properties for LiAlTe2 compound and still awaits experimental confirmations. We have included the spin-orbit interaction (SOI) in our calculations which is known to have significant influence on the electronic and optical properties when heavy elements are present. A weak effect is observed for the studied compound. Keywords: DFT, Wien2k, Chalcopyrite, band gap, dielectric function, thermal properties.

Molar heat capacity of liquid Ti, Al20Ti80 and Al50Ti50 measured in electromagnetic levitation

Temperature dependent isobaric molar heat capacity cP was measured in a containerless way for liquid Ti and two AlTi binary liquid alloys. The technique of electromagnetic levitation was used in combination with laser modulation calorimetry. In all cases, linear temperature dependencies were found: At the corresponding liquidus temperatures, cP equals 49.75(±2.0) J∙K-1mol-1, 57.43(±2.9) J∙K-1mol-1, and 42.60(±2.2) J∙K-1mol-1, for Ti, Al20Ti80 and Al50Ti50, respectively. The respective temperature coefficients amount to -1.67∙10-2J∙K-2mol-1, -2.73∙10-2J∙K-2mol-1, and +7.83∙10-2J∙K-2mol-1. For liquid Ti, there is a good agreement with existing literature data. The results are discussed in relation to the Neumann-Kopp rule.

Establishment of regularities of influence on the specific heat capacity and thermal diffusivity of polymer nanocomposites of a complex of defining parameters

This paper reports a series of experimental studies to establish regularities of the integrated effect exerted on the specific heat capacity of polymer nanocomposites by such factors as the temperature regime of their production, the value of the mass fraction of the filler, and the temperature of the composite material. The studies were conducted for nanocomposites based on polypropylene filled with carbon nanotubes. When obtaining composites, the method of mixing the components in the melt of the polymer was used. During the studies, the temperature of nanocomposites varied from 295 to 455 K, the mass fraction of the filler ‒ from 0.3 to 10 %. The basic parameter of the technological mode for obtaining composite materials, the value of overheating the polymer melt relative to its melting point, varied in the range of 10...75 K. It is shown that the temperature dependence of the specific heat capacity of the considered composites is sensitive to changes in the overheating of the polymer melt only in the region maximum values of the specific heat capacity. Concentration dependences of the specific heat capacity of the considered nanocomposites at different values of their temperature and the level of overheating of the polymer melt have been built. The studies have been carried out to identify the effects of the influence of the above parameters on the coefficient of thermal diffusivity of nanocomposites. It has been established, in particular, that an increase in the level of overheating the polymer could lead to a very significant increase in the coefficient of thermal diffusivity, which is all the more significant the higher the proportion of filler and the lower the temperature of the composite material. It is shown that the level of overheating the polymer melt relative to its melting point is a parameter that can be used as the basis for the creation of polymer composite materials with specified thermophysical properties.

Resistive heating of a shape memory composite: analytical, numerical and experimental study

This work investigates in detail the Joule resistive heating phenomenon of electroactive shape memory composites (SMC) when an electric current is injected at constant power. The SMC is a covalent poly(ϵ-caprolactone) network filled with 3 wt% of multiwall carbon nanotubes. The resistive heating of the SMC is studied by means of surface temperature measurements, analytical formulas and a coupled 3D thermo-electric numerical model. Analytical expressions are derived for the 2D temperature distribution within a parallelepipedic SMC, either with constant or linearly-dependent electrical resistivity. These analytical expressions can be used to investigate the influence of geometrical and material parameters in the steady-state temperature and its distribution across the sample. The results also allow one to identify the parameters that are crucial for predicting the temperature rise due to resistive heating: the temperature dependence of the resistivity has little effect on the steady-state temperature, whereas the thermal conductivity plays a significant role. The time-dependent temperature is shown to be related to the particular temperature dependence of heat capacity. Furthermore, the presence of external objects (clamps or grips) used during the shape memory cycle must be taken into consideration for a certain temperature to be reached since they result in a lower steady-state temperature and a slower resistive heating phenomenon. With the findings presented in this work, accurate resistive heating can be predicted for a SMC upon the injection of an electric current at constant power.

Electron–phonon coupling factor and electron heat capacity of 6H-SiC

ABSTRACT For high-energy single ion events, the relationship between electronic energy loss mechanism and atomic processes is generally described by the inelastic thermal spike model. However, the parameters required for the model are not accurately known and are often estimated from a free electron gas model. To ensure this model is more reliable and predictive, a more accurate calculation for the parameters should be taken. In this paper, the temperature dependence of the electronic heat capacity and electron–phonon coupling factor (e-ph) has been calculated, using density functional theory (DFT). The calculation results demonstrate that the effect of electron thermal excitation on the thermodynamic parameters is sensitive to the bandgap, and these parameters vary immensely with the electron temperature. Besides, to verify the accuracy of obtained parameters, both the swift heavy ions (SHI) irradiation in crystalline 6H-SiC and amorphous 6H-SiC are simulated, using the inelastic thermal spike model. And the results are more consistent with the experiment conclusion, for the obtained parameters by DFT. Hence, the calculated temperature-dependent parameters are more suitable for the inelastic thermal spike model.

Towards fuel composition and properties from Two-dimensional gas chromatography with flame ionization and vacuum ultraviolet spectroscopy

Already low volume (<1mL) test methods facilitate the development of sustainable aviation fuel platforms and higher fidelity computational methods. Here a novel technique with two-dimensional gas chromatography (GCxGC) and Vacuum Ultraviolet (VUV) identification is used to characterize fuel composition and determine properties compared to previous work. Ten properties are predicted, including the temperature dependence of density, viscosity, thermal conductivity, and heat capacity. Property predictions incorporate uncertainty quantification (UQ) from analyte quantification (UQ1), root property uncertainty (UQ2), and the uncertainty associated with isomeric variance (UQ3), when an analyte is not identified via VUV. Comparisons to a previous method illustrate the ability of VUV identification to increase the fidelity of property predictions and decrease uncertainties. This method is applied to a surrogate intended to mimic the first-order properties and composition of a representative Jet A/A-1. In addition to nominal and temperature-dependent properties, the derived cetane number (DCN) of the surrogate is calculated for the distillation fraction evolved. The DCN there is shown to vary across the fraction of fuel distilled. Collectively, this method documents a process to prescreen novel sustainable aviation fuel candidates, facilitate the development of chemical process models, and automate property determinations for computational fluid dynamics.

Exact calculations of the thermal properties of two-electron GaAs quantum dots with inverse-square interactions

In this study, we theoretically scrutinize the effect of the inverse-square interaction on the thermal properties of two electrons trapped in a parabolic GaAs quantum dot. The analytical energy spectrum was used to calculate the thermal properties of the system using the canonical ensemble formalism. It was found that the thermal energy increased with the increase in temperature, while it remained almost constant for sufficiently low temperatures; it was also demonstrated that the inverse-square interaction increased the thermal mean energy. Moreover, the heat capacity increased sharply within a low-temperature window and saturated to the value of 2kB in the high-temperature limit. As expected, entropy increased linearly with increasing temperature. It was also shown that both entropy and heat capacity decreased rapidly when the confinement strength increased (or the dot size decreased) in the low-temperature limit, regardless of the influence of the interaction between the electrons. We also show that the number of allowed states of the system decreased as the interaction strength increased (Z(λ = 0) &gt; Z(λ ≠ 0)). Finally, the stability of the system was investigated through F–T curves. The three-dimensional surface for the temperature-dependent mean energy and heat capacity was also plotted. It should be noted that, for the thermal mean energy, partition function, and Helmholtz free energy, the normal physical behavior of the two-oscillator system with Fermi statistics is recovered for λ → 0. However, heat capacity and entropy show exact two-fermion oscillator system behavior. The most impressive result found in this work is that the inverse-square interaction does not affect the heat capacity and entropy at all despite its noticeable effects on the thermal mean energy. This, in turn, facilitates theoretical studies related to finding the distinctive parameters of quantum dots without going into the heavy calculations resulting from the effects of interactions.

High throughput optimization procedure to characterize vitrification kinetics

We present VITRIFAST, a high throughput optimization procedure to characterize the vitrification kinetics based on calorimetric measurements. By analyzing the temperature dependence of specific heat capacity, the method determines the fictive temperature, Tf, and the enthalpy change during physical aging, ΔH, within only a few seconds. We tested VITRIFAST on the low molecular weight glass-former o−terphenyl (OTP) and on an archetypal glass forming polymer, polystyrene (PS), by analyzing the outcome of two classical sets of experiments. By means of fast scanning calorimetry (FSC), we characterized the vitrification kinetics in a wide range of cooling rates and the isothermal physical aging after vitrification at a given rate. In less than 3 minutes, our method could process 18 different calorimetric scans and provided values of Tf and ΔH in excellent agreement with those reported in the literature. VITRIFAST can be employed in the analysis of the temperature dependence of any type of second order derivative of free energy and represents a tremendous advance in the data analysis of calorimetric scans. The method is particularly helpful for fast scanning calorimetry users, considering the extremely large number of heat capacity scans recorded by this technique within a few minutes.

Magnetostructural transition, magnetocaloric effect and critical exponent analysis in Nd(Co0.8Fe0.2)2 alloy

In the present study, the magnetostructural transition, magnetocaloric effect (MCE) and critical behavior of Nd(Co0.8Fe0.2)2 alloy in the vicinity of ferromagnetic transition were studied. The Rietveld refinement analysis of in-situ synchrotron XRD patterns reveals that the present alloy crystallizes in the cubic phase (space group Fd3̅m) at room temperature and undergoes a structural transition to the tetragonal phase (space group I41/amd) below its Curie temperature. Temperature dependent heat capacity measurements under different applied magnetic fields were carried out to investigate the magnetocaloric properties. The maximum magnetic entropy change (ΔSM) of 5.6 J/kgK and relative cooling power (RCP) of 445.7 J/kg are obtained over the wide working temperature range of 82 K under magnetic field change of 5 T. The corresponding adiabatic temperature change (ΔTad) is evaluated to be 2.9 K under the same magnetic field change. The sample shows metallic behavior with its significant magnetoresistance value of −41.2% around phase transition at magnetic field change of 5 T. These results may make Nd(Co0.8Fe0.2)2 alloy as one of the promising material for refrigeration applications. Moreover, the critical parameters (β, γ, and δ) were deduced independently from the magnetization data by using different techniques such as modified Arrott plot, Kouvel–Fisher method and critical magnetization isotherms. The derived β=0.319, γ =1.214, and δ=4.78 values are found to be consistent with the 3D-Ising class signifying the presence of short-range exchange interactions in this alloy. We have further shown that these exponents follow the M(H, ε)=|(T − TC)/TC |βf±H/|(T − TC)/TC|β+γ scaling equation very well for both the above and below Curie temperature demonstrating that the estimated exponents are unambiguous and are intrinsic to this alloy system.

Study of Thermal Properties of Metal-Filled Nanocompositions Based on Polyethylene

The production of metal-containing nanoparticles is one of the important problems of modern science related to the creation of nanomaterials. Nanocomposites based on polymer matrices and uniformly distributed nanoparticles (quantum dots) isolated from each other in them have unique photoluminescent properties; in addition, polymer matrices are convenient stabilizers of nanoparticle growth and have good mechanical properties. Of the nanoparticles of semiconducting materials, metal chalcogenides (CdS, Cu) are of the greatest interest. In the chemical synthesis of metal sulfides in a polymer medium, H2S or a compound containing active sulfur can act as a sulfiding agent. Samples of nanocomposites based on semiconductor sulfides and polyethylene have been synthesized. The composition, structure and structure of nanoparticles were studied by X-ray phase analysis and spectroscopy. Investigated from thermophysical properties. From studies of the temperature dependence of the heat capacity of the compositions, LDPE and CdS compositions, It can be seen that there is a peak on the curve in the temperature range of 100-2250K, which almost degenerates with an increase in the concentration of the filler. Measurements of the temperature dependence of thermal conductivity and heat capacity revealed the presence of reversible structural rearrangements in polymer composites with metal oxide fillers. Moreover, various methods, within the limits of errors, fix a constant transition temperature of electrical conductivity, thermal conductivity and heat capacity, which speaks in favor of the fact that the basis of all detected anomalies is a single mechanism, i.e. structural rearrangement of defect states of polymer composites.

DFT aspects of the elastic, mechanical, magnetic, thermodynamic and optical properties of Ce3XY perovskites

ABSTRACT We report some unclarified physical properties of Ce3XY (X = Al, In and Y = C, N) inverse cubic perovskites by conducting a density functional theory (DFT) study. The elastic, mechanical, magnetic, thermodynamic and optical properties of these compounds were addressed. Obtained elastic data prove the mechanical stability, elastic anisotropy and brittle mechanical character for all investigated compounds. Vickers hardness values follow the Ce3InC > Ce3AlN > Ce3InN > Ce3AlC sequence. All compounds show ionic bonding except the Ce3AlC in which covalent bonding is dominant. Besides, all compounds exhibit ferromagnetic ordering. The calculated total magnetic moments arise between 2.22μB and 2.67μB. Their magnitudes follow Ce3InN > Ce3AlN > Ce3InC > Ce3AlC range. Temperature dependence of heat capacity, entropy, thermal conductivity and Debye temperature of the compounds exhibit identical characteristics of typical solids. Optical property results suggest that these compounds are both good optical absorbers and conductors, in particular for practical applications in the ultraviolet (UV) region.

Analytical modeling of thermal processes during femtosecond laser pulse action on metallic nanoparticle

The analytical approach has been proposed for the modeling of the thermal processes during the action of femtosecond laser pulse on metallic (gold) nanoparticle with allowance for the temperature dependences of the electron heat capacity and the electron-phonon coupling factor of gold based on thermal excitation of electron density. This leads to novel dependence of the electron-phonon equal temperature and the coupling factor on the maximal electron temperature. Whole process of femtosecond nanoparticle action has been divided into three stages which include firstly the heating of electron system by pulse, secondly the electron-phonon energy exchange and the establishment of the equal temperature of electrons with lattice, and thirdly the nanoparticle cooling with the corresponding analytical description of each stage. The satisfactory agreement with the computer results for femtosecond pulses validates of used analytical approach. This model can be used for the estimation of laser and nanoparticle parameters in the fields of the applications of femtosecond laser pulses.

Heat capacity of lithium tungstate single crystal by DSC calorimetry data in the temperature range of 319-997 K

The heat capacity of lithium tungstate single crystal (Li2WO4) was measured for the first time in the temperature range of 319-997 K. The experiments were carried out by DSC calorimetry. The Li2WO4 single crystal was first grown by low-temperature-gradient Czochralski technique with weight control. The temperature dependence of Li2WO4 heat capacity in the temperature range 319-997 K was monotonic. According to results of our studies, there were no phase transitions in Li2WO4 in the investigated temperature range.