Behavior Of Heat Capacity Research Articles

Qualitatively Different Non‐Quartic Low‐Temperature Heat Capacity Behaviors due to Various Non‐Metallic Solids

Different non‐quartic cryogenic heat capacity dependences can be unambiguously associated with the qualitatively different types of either sub‐quartic or super‐quartic regimes. The simplest way for a prompt association with one of these two alternative regimes is based on a couple of parameters controlling the straight‐line tangents to the material‐specific C(T)/T3 curves in consideration. A representative non‐Debye heat capacity formula is used for performing high‐accuracy fittings of cryogenic heat capacity data sets, including reliable determinations of the material‐specific temperature dependences of effective power function exponents. The cryogenic heat capacity dependences of the exemplary wide bandgap materials AgCl and LiI are found to show pronounced sub‐quartic behaviors, whereas germanium and silicon are seen to pertain to the regime of super‐quartic behavior. These results are in clear contrast to a hypothetical field‐theoretical model published recently by Gusev [R. Soc. Open Sci. 2019, 6, 171285], which suggested an allegedly universal low‐temperature behavior of quartic type. An unprecedented graphical distinction tool is introduced here, consisting in alternative C(T)/T4 data representations, by means of which the qualitative differences between opposite non‐quartic heat capacity behaviors for the materials under study have been visualized in rather pronounced form. A brief discussion is given of preliminary assessments of non‐quartic cryogenic heat capacity behaviors for a larger variety of III–V, II–VI, and I–VII materials.

Heat Capacity and Phase Behavior of Selected Oligo(ethylene glycol)s

This work aims to provide reliable heat capacities for ethylene glycol and selected oligo(ethylene glycol)s (diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and h...

Consequences of residual-entropy hierarchy violation for behavior of the specific heat capacity in frustrated magnetic systems: An exact theoretical analysis.

We investigate in detail the influence of the violation of the strict residual-entropy hierarchy among the neighboring ground states of different orders on the low-temperature behavior of the specific heat capacity in the magnetic frustrated systems in the framework of the exactly solvable antiferromagnetic spin-1/2 Ising model with the multisite interaction in the presence of the external magnetic field on the zigzag ladder. The exact expressions for the residual entropies of all ground states of the model are found, and it is shown that when the strength of the multisite interaction is strong enough then the model exhibits a quite interesting specific situation, namely, that there exist neighboring plateau ground states together with the single-point ground state that separates them, such that the magnetization properties of all of them are different but their entropy per site is the same and equal to zero. It is shown that this fact of the violation of the strict residual-entropy hierarchy between neighboring ground states of different orders leads to the reduction of the possible number of peaks that can appear in the low-temperature behavior of the specific heat capacity in the corresponding regions of the model parametric space. In addition, it is also shown that the absence of the strict residual-entropy hierarchy among neighboring ground states of different orders changes qualitatively the behavior of the specific heat capacity as a function of the external magnetic field, namely, that the typical field-induced sharp double-peak structure in the low-temperature behavior of the specific heat capacity, which is directly related to the very existence of the highly macroscopically degenerated single-point ground states, disappears already for relatively large values of the temperature.

Short-Chain Modified SiO2 with High Absorption of Organic PCM for Thermal Protection.

Organic phase change materials (PCMs) have great potential in thermal protection applications but they suffer from high volumetric change and easy leakage, which require “leak-proof” packaging materials with low thermal conductivity. Herein, we successfully modify SiO2 through a simple 2-step method consisting of n-hexane activation followed by short-chain alkane silanization. The modified SiO2 (M-SiO2) exhibits superior hydrophobic property while maintaining the intrinsic high porosity of SiO2. The surface modification significantly improves the absorption rate of RT60 in SiO2 by 38%. The M-SiO2/RT60 composite shows high latent heat of 180 J·g−1, low thermal conductivity of 0.178 W·m−1·K−1, and great heat capacity behavior in a high-power thermal circuit with low penetrated heating flow. Our results provide a simple approach for preparing hydrophobic SiO2 with high absorption of organic PCM for thermal protection applications.

Heat capacities and thermodynamic functions of the ZIF organic linkers imidazole, 2-methylimidazole, and 2-ethylimidazole

Metal organic frameworks (MOFs) are a novel class of materials that consist of a lattice of metal centers linked by organic molecules. Previously, heat capacities and thermodynamic functions have been reported for a series of crystalline polymorphs of Zn(EtIm)2, a zeolitic imidazolate framework family of MOFs that have potential applications in CO2 sequestration. In those studies, an anomalous trend in the heat capacity and thermodynamic functions was observed that was not predicted. To further investigate these materials and their thermodynamic data, the low-temperature heat capacities of imidazole, 2-methylimidazole, and 2-ethylimidazole, organic linkers that are present in Zn(EtIm)2 and similar materials, were measured by a Quantum Design Physical Property Measurement System (PPMS) from 1.8–300 K. The data collected was fit to theoretical functions below 10 K, orthogonal polynomials from 5–60 K, and a sum of Debye and Einstein functions above 50 K. These functions were used to generate Cp,m°, Δ0TSm°, Δ0THm°, and Φm° values at smoothed temperatures from 0–300 K. This investigation revealed the presence of a second-order phase transition in 2-ethylimidazole that may yield insight into the anomalous heat capacity behavior present in Zn(EtIm)2.

Heat-capacity measurements of sandstone at high temperatures

To evaluate geothermal energy generation systems, we must predict the amount of heat present and the rate at which it can be extracted. These two factors—amount of heat and recovery rate—in turn depend on the basic physical properties of the reservoir rocks. The amount of heat present in a reservoir depends on the heat capacity CP of the rocks. The heat capacity of the rocks is needed to evaluate energy storage, Q = (1 − ϕ)ρCP(T)T, where ϕ is the porosity, ρ is the density, CP is the heat capacity, and T is the temperature. For global heat balances, the mean specific heat between two extreme temperatures T1 and T2, can be defined as \(Q = \frac{1}{{T_{2} - T_{1} }}\int\nolimits_{{T_{1} }}^{{T_{2} }} {C_{P} \left( T \right)dT}\), where CP(T) is the temperature-dependence of the heat capacity. For dynamic processes, the value of heat-capacity at each given temperature is needed. The area under a CP(T) curve between any two temperature limits yields an enthalpy change as \(\Delta H = \int\nolimits_{{T_{1} }}^{{T_{2} }} {C_{P} \left( T \right)dT}\). In the present work we have detailed study of the temperature dependence of the heat capacity (CP) of sandstone over the temperature range from 308 to 763 K using a differential scanning calorimeter model of 204 F1. The combined expanded uncertainty of the heat capacity measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 1%. A rapid increase (from 1.06 to 1.85 kJ kg−1 K−1) of the measured heat capacities above the classical value (3R) in the high-temperature range above 575 K was observed. This increase at high temperatures can be explained as being due to microstructural changes during heating of the sample (the microstructural effect), which was confirmed by thermal expansion coefficient measurements. The effect of microstructural changes (“thermal cracking”) on the temperature behavior of heat-capacity of sandstone was studied. Theoretically-based correlations for the heat capacity were adopted to accurately represent the measured data. The measured CP(T) data for sandstone were used to check the accuracy, predictive capability, and applicability of various correlation models proposed in the literature. The proposed correlation equations for the heat capacity are based on the present experimental data that have been critically assessed for consistency with other measured properties and for agreement with theory whenever possible.

Heat capacity and entropy behavior of andradite: a multi-sample and −methodological investigation

Heat capacity and entropy behavior of andradite: a multi-sample and −methodological investigation

Behavior of Isobaric Heat Capacity of Pentafluoroethane in the Gas Phase

The isobaric specific heat capacity cp of gaseous pentafluoroethane was measured and the behavior was presented. With a flow calorimeter, 29 cp data of pentafluoroethane were measured at temperatures T from (303 to 343) K and at pressures p from (0.5 to 2.4) MPa. Some of them were measured in the immediate vicinity of the saturation curve. The expanded uncertainties (k = 2) of the temperature measurements U(T) and the pressure measurements U(p) are estimated to be below 50 mK and 11 kPa, respectively. That for cp measurements Uc(cp) is assessed to extend from (14 to 60) J·kg–1·K–1. Then, the cp measurements including the previous 12 measurements were compared with some available equations of state. Using these confirmed data, the cp behaviors of gaseous pentafluoroethane were presented in a cp–p diagram.

Applicability of effective field theory cluster approximations for investigation of geometrically frustrated magnetic systems: Antiferromagnetic model on kagome lattice

We investigate the antiferromagnetic spin-1∕2 Ising model in the presence of the external magnetic field on the geometrically frustrated kagome lattice using the effective field theory cluster approximation up to the size of the cluster consisting of 12 connected sites which form typical basic geometrical structure of the kagome lattice. The magnetization properties, systems of the ground states, as well as the specific heat capacity behavior of the model are investigated depending on the cluster size. It is shown that properties of the model related to the frustration, such as the formation of discrete system of ground states, strongly depend on the used cluster approximation. It is shown that besides physically relevant ground states the model also exhibits the existence of ground states which are related to the used effective field theory technique and should disappear in the limit n→∞ of the n-site cluster approximation with simultaneous formation of physically relevant ground states of the Ising model on the kagome lattice. The unphysical origin of these ground states is also demonstrated by the low temperature behavior of the specific heat capacity which exhibits even inverse Schottky peaks with negative values of the specific heat capacity which are reduced with increasing of the cluster size approximation towards physically acceptable behavior. For completeness, the dependence of the position of the critical temperature and the behavior of the spontaneous magnetization and specific heat capacity of the ferromagnetic model in the zero external magnetic field on the size of the cluster approximation is also briefly discussed.

Asymmetric liquid-liquid criticality in the ideal volumetric mixing approximation

Abstract We address the question on the validity of the ideal volumetric mixing approximation, a customarily used approach to analyze liquid-liquid phase transitions. Thus, liquid-liquid coexistence curves for the binary mixture composed by nitromethane and 3-pentanol were obtained from direct single-phase mass density measurements as a function of temperature. A reasonable agreement with previously reported data obtained from refractive index measurements has been found, indicating that assuming ideal mixing is rather reasonable. Furthermore, the implications of the ideal volumetric mixing approximation on asymmetric liquid-liquid criticality are explored in the framework of complete scaling formulation, with emphasis on the coexistence curves in the mole fraction-temperature and volume fraction-temperature planes as well as on the behaviour of the isobaric heat capacity per particle and per unit volume and the associated Yang-Yang-type anomalies.

Heat capacity and phase behaviour of {pentaethylene glycol monoheptyl ether + water} system. Two-point scaling approach

The miscibility in the {pentaethylene glycol monoheptyl ether (C7E5) + water} system was investigated by differential scanning calorimetry (DSC). The specific heat capacities cp of chosen nonionic amphiphile (C7E5) aqueous solutions have been measured within temperature range 273.15–338.15 K over wide concentration range. The apparent and partial molar heat capacities were calculated to analyze the aggregation process taking place in the solution. In order to study some additional information on the solution structure two-point scaling theory was used. On the base of temperature dependences of differential heat flow, phase coexistence curve was determined.

Multipeak low-temperature behavior of specific heat capacity in frustrated magnetic systems: An exact theoretical analysis.

We investigate in detail the process of formation of the multipeak low-temperature structure in the behavior of the specific heat capacity in frustrated magnetic systems in the framework of the exactly solvable antiferromagnetic spin-1/2 Ising model with the multisite interaction in the presence of the external magnetic field on the kagome-like Husimi lattice. The behavior of the entropy of the model is studied and exact values of the residual entropies of all ground states are found. It is shown that the multipeak structure in the behavior of the specific heat capacity is related to the formation of the multilevel hierarchical ordering in the system of all ground states of the model. Direct relation between the maximal number of peaks in the specific heat capacity behavior and the number of independent interactions in studied frustrated magnetic system is identified. The mechanism of the formation of the multipeak structure in the specific heat capacity is described and studied in detail, and it is generalized to frustrated magnetic systems with arbitrary numbers of independent interactions.

Bizarre behavior of heat capacity in crystals due to interplay between two types of anharmonicities.

The heat capacity of classical crystals is determined by the Dulong-Petit value CV ≃ D (where D is the spatial dimension) for softly interacting particles and has the gas-like value CV ≃ D/2 in the hard-sphere limit, while deviations are governed by the effects of anharmonicity. Soft- and hard-sphere interactions, which are associated with the enthalpy and entropy of crystals, are specifically anharmonic owing to violation of a linear relation between particle displacements and corresponding restoring forces. Here, we show that the interplay between these two types of anharmonicities unexpectedly induces two possible types of heat capacity anomalies. We studied thermodynamics, pair correlations, and collective excitations in 2D and 3D crystals of particles with a limited range of soft repulsions to prove the effect of interplay between the enthalpy and entropy types of anharmonicities. The observed anomalies are triggered by the density of the crystal, changing the interaction regime in the zero-temperature limit, and can provide about 10% excess of the heat capacity above the Dulong-Petit value. Our results facilitate understanding effects of complex anharmonicity in molecular and complex crystals and demonstrate the possibility of new effects due to the interplay between different types of anharmonicities.

Anomalous Behavior of Electronic Heat Capacity of Strongly Correlated Iron Monosilicide

The paper deals with the electronic heat capacity of iron monosilicide FeSi subjected to semiconductor–metal thermal transition during which the formation of its spintronic properties is observed. The proposed model which considers pd-hybridization of strongly correlated d-electrons with non-correlated p-electrons, demonstrates a connection of their contribution to heat capacity in the insulator phase with paramagnon effects and fluctuations of occupation numbers for p- and d-states. In a slitless state, the temperature curve of heat capacity is characterized by a maximum appeared due to normalization of the electron density of states using fluctuating exchange fields. At higher temperatures, a linear growth in heat capacity occurs due to paramagnon effects. The correlation between the model parameters and the first-principles calculation provides the electron contribution to heat capacity, which is obtained from the experimental results on phonon heat capacity. Anharmonicity of phonons is connected merely with the thermal expansion of the crystal lattice.

4a-YF-7 正常-不整合相転移に伴う熱容量異常の臨界現象

4a-YF-7 正常-不整合相転移に伴う熱容量異常の臨界現象

Investigation on standard molar enthalpy of combustion, specific heat capacity and thermal behavior of methionine

The standard molar enthalpy of combustion of methionine was determined to be − 6661.03 kJ mol−1 by XRY-1C microcomputer oxygen bomb calorimeter. The standard molar enthalpy of formation was calculated to be 3121.35 kJ mol−1 based on the standard molar combustion enthalpy. The thermal stability behavior of methionine was studied by the thermal gravimetric analysis. The results show that melting process of methionine was accompanied by the decomposition reaction in the temperature range of 500.15–520.15 K, displayed one-stage decomposition process. The absorb heat of methionine was obtained to be 974.34 kJ mol−1 (6530.00 J g−1) at 550.51 K by DSC-60 differential scanning calorimetry. Moreover, the specific heat capacity of methionine from 373.15 to 453.15 K in the solid state was measured, and then the relationship between the constant pressure specific heat capacity Cp and the temperature has been established. These data provide a thermodynamic basis for process development, engineering design and industrial production of methionine.

Enhancement of electrocaloric response through quantum effects

A semiclassical approach that incorporates quantum mechanical behavior of heat capacity in direct caloric effect simulations is proposed. Application of this methodology to study electrocaloric effect in prototypical ferroelectrics ${ \rm PbTiO_3 }$, and ${ \rm BaTiO_3 }$, reveals severe underestimation of electrocaloric response at lowest temperatures by classical simulations. The discrepancy between semiclassical and classical results are found to be largest in ferroics with Debye temperature exceeding the Curie point. A route to enhance electrocaloric effect by tuning the Debye temperature in composite materials is proposed.

Thermodynamics of disordering in Au3Cu

The enthalpy of disordering, as well as the vibrational and the configurational entropy of disordering of stoichiometric Au3Cu were investigated by heat capacity measurements using differential scanning and relaxation calorimetry. Beside these calorimetric methods, the density functional theory was used to calculate the enthalpy of disordering at zero K. The time scale of the ordering reaction was larger than that of the calorimetric experiment resulting in non-equilibrated heat capacity data. Integrating these data within appropriate limits delivered, however, equilibrium values for the enthalpy of disordering, from which the heat capacity and the entropy of disordering were calculated. Investigating the low-temperature heat capacity behaviour of ordered and disordered samples enabled the separation of vibrational and configurational parts of the entropy. The enthalpy of disordering in Au3Cu is lower than half of that in Cu3Au and reaches a maximum value of 1.46 kJ mol−1. The entropy of disordering at 650 K has a value of 0.58 R with a small vibrational part of 0.02 R. The determined configurational entropy reaches the ideal configurational entropy of a disordered A3B alloy of 0.562 R at 650 K. Above 650 K, the ideal value is slightly exceeded.

Highly macroscopically degenerated single-point ground states as source of specific heat capacity anomalies in magnetic frustrated systems

Anomalies of the specific heat capacity are investigated in the framework of the exactly solvable antiferromagnetic spin-1/2 Ising model in the external magnetic field on the geometrically frustrated tetrahedron recursive lattice. It is shown that the Schottky-type anomaly in the behavior of the specific heat capacity is related to the existence of unique highly macroscopically degenerated single-point ground states which are formed on the borders between neighboring plateau-like ground states. It is also shown that the very existence of these single-point ground states with large residual entropies predicts the appearance of another anomaly in the behavior of the specific heat capacity for low temperatures, namely, the field-induced double-peak structure, which exists, and should be observed experimentally, along with the Schottky-type anomaly in various frustrated magnetic system.

Capacity of entanglement and the distribution of density matrix eigenvalues in gapless systems

We propose that the properties of the capacity of entanglement (COE) in gapless systems can efficiently be investigated through the use of the distribution of eigenvalues of the reduced density matrix (RDM). The COE is defined as the fictitious heat capacity calculated from the entanglement spectrum. Its dependence on the fictitious temperature can reflect the low-temperature behavior of the physical heat capacity, and thus provide a useful probe of gapless bulk or edge excitations of the system. Assuming a power-law scaling of the COE with an exponent $\alpha$ at low fictitious temperatures, we derive an analytical formula for the distribution function of the RDM eigenvalues. We numerically test the effectiveness of the formula in relativistic free scalar boson in two spatial dimensions, and find that the distribution function can detect the expected $\alpha=3$ scaling of the COE much more efficiently than the raw data of the COE. We also calculate the distribution function in the ground state of the half-filled Landau level with short-range interactions, and find a better agreement with the $\alpha=2/3$ formula than with the $\alpha=1$ one, which indicates a non-Fermi-liquid nature of the system.