Temperature Dependence Of Specific Heat Research Articles

Presence versus absence of two-dimensional Fermi surface anomalies

We theoretically consider Fermi surface anomalies manifesting in the temperature-dependent quasiparticle properties of two-dimensional (2D) interacting electron systems, comparing and contrasting with the corresponding three-dimensional (3D) Fermi liquid situation. In particular, employing microscopic many-body perturbative techniques, we obtain analytically the leading-order and the next-to-leading-order interaction corrections to the renormalized effective mass for three distinct physical interaction models: electron-phonon, electron-paramagnon, and electron-electron Coulomb coupling. We find that the 2D renormalized effective mass does not develop any Fermi surface anomaly due to electron-phonon interaction, manifesting $\mathcal{O}({T}^{2})$ temperature correction and thus remaining consistent with the Sommerfeld expansion of the noninteracting Fermi function, in contrast to the corresponding 3D situation where the temperature correction to the renormalized effective mass has the anomalous ${T}^{2}logT$ behavior. In contrast, both electron-paramagnon and electron-electron interactions lead to the anomalous $\mathcal{O}(T)$ corrections to the 2D effective mass renormalization in contrast to ${T}^{2}logT$ behavior in the corresponding 3D interacting systems. We provide detailed analytical results, and comment on the conditions under which a ${T}^{2}logT$ term could possibly arise in the 2D quasiparticle effective mass from electron-phonon interactions. We also compare results for the temperature-dependent specific heat in the interacting 2D and 3D Fermi systems, using the close connection between the effective mass and specific heat.

Thermoelectric Properties and Thermal Stability of Nanostructured Thermoelectric Materials on the Basis of PbTe, GeTe, and SiGe

We have developed compositions and methods for obtaining effective medium-temperature nanostructured thermoelectric materials (TEMs): PbTe (doped by 0.2 wt % PbI2, 0.3 wt % Ni), GeTe (doped by 7.4 wt % Bi), high-temperature Si0.8Ge0.2 (doped by 1.7 wt % P) and Si0.8Ge0.2 (doped by 0.5 wt % B). Using scanning electron microscopy, the composition and structure of the materials are studied. The temperature dependence of the electrical conductivity and thermoelectric power of TEMs are explored. The thermal conductivity of TEMs are studied by the absolute stationary method. The components of thermal conductivity are determined. A decrease in thermal conductivity in nanostructured materials by 10–15% in comparison with the usual structure due to phonon heat transfer has been found. The obtained data are used to calculate the thermoelectric figure of merit (Z) and parameter ZТ. For nanostructured TEMs based on PbTe, GeTe, and n-type Si0.8Ge0.2, the temperature dependences of specific heat have been studied for the first time using differential scanning calorimetry (DSC). With the help of repeated DSC measurements, it has been found that nanostructured TEMs are thermally stable in the working temperature ranges. Thermogravimetric analysis is carried out and temperatures are determined at which a significant TEM sublimation occurs. The ranges of operating temperatures at which the investigated TEMs have the maximum efficiency and thermal stability have been determined. This is urgent in modeling multisectional thermoelements operating in a wide temperature range.

Time fractional heat transfer analysis in thermally sensitive functionally graded thick hollow cylinder with internal heat source and its thermal stresses

The aim of this work is to investigate the time fractional thermoelastic state of a thermally sensitive functionally graded thick hollow cylinder subjected to internal heat source. Convection boundary conditions are applied on the curved surface of cylinder also sectional heating is assumed on the lower surface. The material properties except density and Poisson’s ratio are assumed to be dependent on temperature. Kirchhoff’s variable transformation is used to reduce the nonlinear heat conduction with temperature dependent thermal conductivity and specific heat capacity to linear form. Further the solution of linear form is obtained by using integral transform technique in the form of Bessel’s and trigonometric functions. All physical and mechanical quantities are taken as dimensional for the theoretical analysis whereas for numerical computations non-dimensional parameters are assumed. Numerical results of temperature change and stress distribution are illustrated graphically for ceramic-metal-based functionally graded materials and shown in figures with the help of Mathematica software.

Weak itinerant ferromagnetism and non-Fermi liquid behavior in Ni-TM (TM = Cr, Nb) alloys near critical concentration

We report a comprehensive study on the magnetic, electrical and thermal properties of Ni100−x TM x (TM = V, Cr, Nb,) alloys around their critical concentration. Analysis of field and temperature dependence magnetization data suggests a weak itinerant ferromagnetic behavior in x = 8 and 10 compositions and the ferromagnetic ordering suppresses in the concentration range 10 < x < 12. Further, the temperature dependence of specific heat shows an unusual low temperature variation with an enhanced Sommerfeld coefficient, γ, with a signature of non-Fermi-liquid (NFL) behavior close to critical concentration. Further, the enhancement in Kadowaki–Woods ratio suggests it to be a strongly correlated electron system near critical concentration. Present analysis of experimental data consistently revealed that the NFL behavior is caused by spin fluctuations near critical concentration. The temperature dependencies of the electrical resistivity, the magnetization and linear term of the electronic specific heat appear to follow the theoretical predictions of a quantum phase transition and it is tempting to suggest that the presently studies Ni-rich alloys can be candidates for the observation of Griffith phase.

Single-crystal investigations on the multiferroic materialLiFe(WO4)2

The crystal and magnetic structure of multiferroic LiFe(WO$_4$)$_2$ were investigated by temperature and magnetic-field dependent specific heat, susceptibility and neutron diffraction experiments on single crystals. Considering only the two nearest-neighbour magnetic interactions, the system forms a $J_1$, $J_2$ magnetic chain but more extended interactions are sizeable. Two different magnetic phases exhibiting long-range incommensurate order evolve at $T_{\text{N}1}\approx 22.2 \text{ K}$ and $T_{\text{N}2}\approx 19 \text{ K}$. First, a spin-density wave develops with moments lying in the $ac$ plane. In its multiferroic phase below $T_{\text{N}2}$, LiFe(WO$_4$)$_2$ exhibits a spiral arrangement with an additional spin-component along $b$. Therefore, the inverse Dzyaloshinskii-Moriya mechanism fully explains the multiferroic behavior in this material. A partially unbalanced multiferroic domain distribution was observed even in the absence of an applied electric field. For both phases only a slight temperature dependence of the incommensurability was observed and there is no commensurate phase emerging at low temperature or at finite magnetic fields up to $6\text{ T}$. LiFe(WO$_4$)$_2$ thus exhibits a simple phase diagram with the typical sequence of transitions for a type-II multiferroic material.

An experimental and straightforward approach to simultaneously estimate temperature-dependent thermophysical properties of metallic materials

This article describes an experimental and straightforward technique towards the simultaneous estimation of temperature-dependent thermal conductivity and specific heat of metals. The thermal model is based on transient nonlinear one-dimensional heat conduction across a metallic sample, which is subject to a constant heat flux on the upper side, and insulated on the bottom side. The thermal analyses are performed in plates of 304 stainless steel and WC10Co cemented carbide. The Levenberg–Marquardt method is employed to provide the solution to an inverse heat conduction problem capable of simultaneously evaluating the temperature-dependent thermophysical properties using transient temperature measurements. Through sensitivity analysis, it is possible to obtain prior information about estimation feasibility and establish all experimental aspects. The imperfect contact at the heater-plate interface causes contact resistance effect, which is considered a reducing agent on heat flux. Beck's nonlinear function minimization technique is used to confirm the reliability of the inverse estimation technique by using the achieved outcomes to recover the heat flux imposed on the test plate. Furthermore, the statistical study into confidence bounds and comparison with literature reveal the robustness of the results. Finally, the accuracy of the developed approach is investigated through the analysis of the errors deriving from experimental and numerical procedures.

New insights into temperature-dependent ice properties and their effect on ice shell convection for icy ocean worlds

Ice shell dynamics are a critical control on the habitability of icy ocean worlds. Here, we present a systematic study evaluating the effect of temperature-dependent material properties on these dynamics. We review the published thermal conductivity data for ice, which demonstrates that the most commonly used conductivity model in planetary science represents a lower bound. We propose a new model for thermal conductivity that spans the temperature range relevant to the ice shells of ocean worlds. This increases the thermal conductivity at low temperatures near the surface by about a fifth. We show that such an increase in thermal conductivity near the cold surface favors conduction over convection in the ice shell of Europa. Furthermore, we find that including temperature dependent specific heat capacity decreases the energy stored in the conductive lid. Thus, the timescale for ice shell response to thermal perturbations is reduced by approximately one third. An ice shell that is more sensitive to thermal perturbations may help to explain surface features such as chaotic terrains which require large additions of energy to the near-surface ice.

Bismuth Doping Alters Structural Phase Transitions in Methylammonium Lead Tribromide Single Crystals.

We study the effects of bismuth doping on the crystal structure and phase transitions in single crystals of the perovskite semiconductor methylammonium lead tribromide, MAPbBr3. By measuring the temperature-dependent specific heat capacity (Cp), we find that as the Bi doping increases, the phase transition assigned to the cubic to tetragonal phase boundary decreases in temperature. Furthermore, after doping we observe one phase transition between 135 and 155 K, in contrast to two transitions observed in the undoped single crystal. These results appear strikingly similar to previously reported effects of mechanical pressure on perovskite crystal structure. Using X-ray diffraction, we show that the lattice constant decreases as Bi is incorporated into the crystal, as predicted by density functional theory. We propose that bismuth substitutional doping on the lead site is dominant, resulting in BiPb+ centers that induce compressive chemical strain that alters the crystalline phase transitions.

PHYSICAL EFFECTS OF VARIABLE FLUID PROPERTIES ON GASEOUS SLIP-FLOW THROUGH A MICRO-CHANNEL HEAT SINK

Physical effects induced in micro-convective gaseous slip-flow due to variation in fluid properties are numerically examined in this paper. The problem is particularly simulated for slip-flow through a micro-channel heat sink (MCHS) having constant heat flux supplied from the wall under hydrodynamically and thermally fully developed flow (FDF) conditions. It is observed that the Nusselt number (Nu) for slip-flow is significantly higher than the no-slip-flow condition and Nu is significantly affected due to variable fluid properties (VFP). Four different cases of VFP are studied in order to investigate their effects individually. Pressure and temperature dependent density (ρ(p, T)) variation flattens the axial velocity profile in radial direction (u(r)) profile which promotes faster-moving particles close to the wall which considerably enhances Nu. The incorporation of temperature-dependent viscosity (μ(T)) variation marginally enhances Nu along the flow. Incorporation of temperature-dependent thermal conductivity (k(T)) variation highly augments Nu due to higher ρ and higher k fluid near to the wall and the incorporation of temperature-dependent specific heat at constant pressure (Cp(T)) variation reduces Nu due to lower k fluid near to the wall. The investigation also shows that the pressure drop significantly deviates from no-slip to slip condition. Furthermore, the effects of VFP on the gauge static pressure drop (Δpg) and slip velocity are also examined. The incorporation of μ(T) and k(T) variations trivially affects the Δpg and slip velocity. However, the incorporation of Cp(T) variation significantly affects the Δpg and slip velocity.

Distribution of RKKY coupling value in 1D crystal with disorder. Specific heat in XY model

The presence of disorder in one-dimensional crystals leads to the localization of all charge carriers and the calculation of the indirect exchange interaction (Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction) cannot be performed perturbatively on disorder. In two and three-dimensional systems it makes sense to calculate the magnitude of RKKY interaction perturbatively treating nearly free carriers scattering on the random potential, and this approach results in a rather high magnitude of the exchange interaction due to interference effects similar to weak localization. We show that in one-dimensional systems the indirect exchange interaction should be described as a random value with heavy-tail distribution function, which is calculated in this work, on scales of carriers localization length. We also demonstrate that heavy tails and the absence of a characteristic value of RKKY interaction magnitude leads to a significant change in observables for these systems. We calculate a specific heat for the one-dimensional XY model taking into account the effect of disorder and assuming that typical distance between impurities exceeds the localization length. In contrast to an ideal system, where specific heat temperature dependence has a peak at a certain temperature proportional to exchange constant describing characteristic energy scale, disorder eliminates the peak as soon as there is no characteristic excitation energy in this case anymore.

Unique magnetic properties of Nd based cuprate francisite: Major enhancement upon Co doping

To understand the physical mechanism of intralayer ferromagnetic (FM) and interlayer antiferromagnetic (AFM) interactions in quasi-two-dimensional model of a real three-dimensional system, rare earth (RE)-Nd based cuprate francisite, Cu3Nd(SeO3)2O2Cl (NdCufr) was doped with Co and studied using structural (X-ray diffraction technique), magnetic (temperature and field dependent magnetization and specific heat measurements) and local structural (X-ray absorption technique) techniques supported by first principle theoretical calculation. The structure of the samples is orthorhombic and doped specimens indicate more or less substitutional incorporation of Co at Cu site. The magnetic properties highlighted with two transitions, viz. AFM to paramagnetic (PM) transition around 30 K and a spin reorientation transition (SRT) below 10 K. Two phenomena viz. magnetic hysteresis below SRT and magnetic field induced metamagnetic transition (MMT) were observed. Co doping significantly enhanced these two phenomena in addition to change the transition temperatures. The concomitant change and enhancement of magnetic properties by Co doping has been interpreted using splitting scheme of Cu-d and Nd-f states. The local structure study corroborates the overall findings and detects the cause of unexpected trend of magnetism with increasing Co doping.

Computational Investigation of Protein Photoinactivation by Molecular Hyperthermia.

To precisely control protein activity in a living system is a challenging yet long-pursued objective in biomedical sciences. Recently, we have developed a new approach named molecular hyperthermia (MH) to photoinactivate protein activity of interest without genetic modification. MH utilizes nanosecond laser pulse to create nanoscale heating around plasmonic nanoparticles to inactivate adjacent protein in live cells. Here we use a numerical model to study important parameters and conditions for MH to efficiently inactivate proteins in nanoscale. To quantify the protein inactivation process, the impact zone is defined as the range where proteins are inactivated by the nanoparticle localized heating. Factors that reduce the MH impact zone include the laser pulse duration, temperature-dependent thermal conductivity (versus constant properties), and nonspherical nanoparticle geometry. In contrast, the impact zone is insensitive to temperature-dependent material density and specific heat, as well as thermal interface resistance based on reported data in the literature. The low thermal conductivity of cytoplasm increases the impact zone. Different proteins with various Arrhenius kinetic parameters have significantly different impact zones. This study provides guidelines to design the protein inactivation process by MH.

On the solutions of a phase change problem with temperature-dependent thermal conductivity and specific heat

Explicit solutions of similarity-type are obtained for a model conduction heat transfer with phase change into a semi-infinite slab, where the thermal conductivities and specific heats of both phases are a linear function of the temperature. The lower and upper bounds for the solutions of this model are also obtained.

Theoretical Evaluation of the Melting Efficiency for the Single-Screw Micro-Extrusion Process: The Case of 3D Printing of ABS

One of the challenges for single-screw micro-extrusion or additive manufacturing (AM), thus 3D printing, of polymers is controlling the melting efficiency so that energy and equipment costs can be minimized. Here, a numerical model is presented for AM process design, selecting acrylonitrile–butadiene–styrene (ABS) as viscoelastic reference polymer. It is demonstrated that AM melting is different compared to conventional melting due to variation in extrusion dimensions, leading to a different balance in heating by conduction and viscous heat dissipation as caused by the shearing between the melt layers in the associated film layer near the barrel. The thickness of this melt film layer is variable along the screw length, and it is shown that simplified models assuming an overall average value are too approximate. It is highlighted that the screw frequency, pitch angle and compression ratio are important process parameters to control the point of melt finalization. In addition, the power-law index reflecting the shear thinning nature of the polymer melt is showcased as a key parameter. Moreover, AM process results assuming constant and temperature dependent specific heat capacities and thermal conductivities are compared. The current work opens the door for on-line AM process control, addressing all relevant operating and material parameters.

Signatures of magnetostriction and spin-phonon coupling in magnetoelectric hexagonal15R−BaMnO3

Spin-phonon coupling, the interaction of spins with surrounding lattice is a key parameter to understand the underlying physics of multiferroics and engineer their magnetization dynamics. Elementary excitations in multiferroic materials are strongly influenced by spin-phonon interaction, making Raman spectroscopy a unique tool to probe these coupling(s). Recently, it has been suggested that the dielectric and magnetic properties of 15R-type hexagonal BaMnO3 are correlated through the spin-lattice coupling. Here, we report the observation of an extensive renormalization of the Raman spectrum of 15R-BaMnO3 at 230 K, 280 K, and 330 K. Magnetic measurements reveal the presence of a long-range and a short-range magnetic ordering in 15R-BaMnO3 at 230 K and 330 K, respectively. The Raman spectrum shows the appearance of new Raman modes in the magnetically ordered phases. Furthermore, an additional Raman phonon appears below ~ 280 K, possibly arising from a local lattice-distortion due to the displacement of Mn-ions, that exhibits anomalous shift with temperature. The origin of the observed renormalization and phonon anomalies in Raman spectra are discussed based on the evidences from temperature- and magnetic-field-dependent Raman spectra, temperature-dependent x-ray diffraction, magnetization, and specific heat measurements. Our results indicate the presence of magnetostriction and spin-phonon coupling in 15R-BaMnO3 thus suggesting that the optical phonons are strongly correlated to its magnetoelectric properties.

Dielectric ordering of water molecules arranged in a dipolar lattice

Intermolecular hydrogen bonds impede long-range (anti-)ferroelectric order of water. We confine H2O molecules in nanosized cages formed by ions of a dielectric crystal. Arranging them in channels at a distance of ~5 Å with an interchannel separation of ~10 Å prevents the formation of hydrogen networks while electric dipole-dipole interactions remain effective. Here, we present measurements of the temperature-dependent dielectric permittivity, pyrocurrent, electric polarization and specific heat that indicate an order-disorder ferroelectric phase transition at T0 ≈ 3 K in the water dipolar lattice. Ab initio molecular dynamics and classical Monte Carlo simulations reveal that at low temperatures the water molecules form ferroelectric domains in the ab-plane that order antiferroelectrically along the channel direction. This way we achieve the long-standing goal of arranging water molecules in polar order. This is not only of high relevance in various natural systems but might open an avenue towards future applications in biocompatible nanoelectronics.

Crystal electric field effects and heavy-fermion behavior in cubic PrCu2Au3 compound

We report the crystal structure as well as the magnetic, electronic and transport properties of PrCu2Au3 which crystallizes in the MgCu4Sn-type structure with the cubic space group F4¯3m (No. 216). In this structure, the Pr3+ ion sits on a lattice site with the cubic Td symmetry which dictates the crystal electric field (CEF) splitting of the Hund’s 3H4 ground multiplet into four levels. The sample has been investigated by measurements of temperature dependences of specific heat, Cp(T), electrical resistivity, ρ(T), magnetic susceptibility, χ(T), isothermal magnetization, M(B,T), thermal conductivity, κT(T) and thermoelectric power, S(T). χ(T) follows a Curie-Weiss behavior above 100 K with an effective magnetic moment, μeff = 3.3 μB/Pr which is comparable to a calculated value of 3.58 μB/Pr for a free Pr3+ ion and a Weiss temperature, θCW = 15.70 K indicating a dominant ferromagnetic interaction. From the analysis of M(B,T) and the 4f-electron derived specific heat (C4f(T)) results, the CEF ground state is a Γ5 magnetic triplet and the CEF energy scheme is presented. The Sommerfeld coefficient, γ estimated from the low-temperature C4f(T) is 304 mJ/(mol K2) indicating a mass enhancement of the conduction electrons at low temperatures. Further analysis of the heavy fermion properties based on the Sommerfeld-Wilson ratio supports the formation of a heavy fermion state in PrCu2Au3. However, the absence of an enhancement in S/T at low temperatures possibly suggests a weak correlation between the conduction electrons and the 4f-electrons at the Fermi energy. The thermal transport properties suggest that PrCu2Au3 is likely a compensated metal.

The effect of rare-earth Gd-substitution on the structural, magnetic and specific heat properties in orthorhombic DyMnO3 ceramics

The acrylamide polymer gel template method has been adopted to synthesize single phase Dy1–xGdxMnO3 (DGMO, x= 0, 0.05, 0.1, 0.15, 0.2) ceramics. The Rietveld refinement of x-ray diffraction patterns recorded at room temperature suggests that DGMO ceramics are stabilized in an orthorhombic crystal structure with a Pnma space group. Gd3+ cations play an important role in stabilizing the orthorhombic phase and the unit cell volume increases with x. We report the phonon spectra of pure and Gd-substituted DyMnO3 (DMO) and their mode assignments. Raman modes are softened with x due to the relaxation in the stiffness constants upon the increase in the volume of the unit cell. The magnetic transition temperatures corresponding to TN(Dy) and Tlock decrease with the increase in Gd concentration as inferred from the temperature dependent magnetization data (M–T curve). The magnetization value increases below TN(Dy) with the increase in the Gd concentration as observed from the M–T plot. The magnetic hysteresis loop is fitted to extract ferromagnetic and antiferromagnetic/paramagnetic contributions for each composition x. Fittings of M–H loops indicate the increase in the magnetic contribution below TN(Dy) upon increasing the Gd dopant concentrations, while that decreases above TN(Dy). The temperature dependent specific heat data identifies these magnetic transition temperatures TN(Dy), Tlock and TN(Mn). Furthermore, magnetic field dependencies on TN(Dy), Tlock and TN(Mn) are studied in an elaborate manner. Both DMO and DGMO samples are found to be viable candidates for magnetic refrigeration applications in cryogenic temperature region.

Thermodynamic Properties of Vanadium Oxypentafluoride (IV) (NH4)3VOF5

The (NH4)3VOF5 crystals have been synthesized and their homogeneity and single-phase structure has been established by the X-ray diffraction, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy studies. The investigations of the temperature dependences of specific heat, entropy, strain, and pressure susceptibility show the occurrence of three phase transitions caused by the structural transformations in the (NH4)3VOF5 crystals. The T–p phase diagram shows the temperature limits of stability of the crystalline phases implemented in (NH4)3VOF5. The optical and dielectric studies disclose the ferroelastic nature of the phase transitions. An analysis of the experimental data together with the data on the isostructural (NH4)3VO2F4 crystal makes it possible to distinguish the physical properties of oxyfluorides containing vanadium of different valences (IV and V).

Exceedingly small moment itinerant ferromagnetism of single crystalline La5Co2Ge3

Single crystals of monoclinic La$_{5}$Co$_{2}$Ge$_{3}$ were grown using a self-flux method and were characterized by room-temperature powder X-ray diffraction, anisotropic temperature and field dependent magnetization, temperature dependent resistivity, specific heat, and muon spin rotation. La$_{5}$Co$_{2}$Ge$_{3}$ has a Curie temperature ($T_\mathrm{C}$) of 3.8~K and clear signatures of ferromagnetism in magnetization and $\mu SR$ data, as well as a clear loss of spin disorder scattering in resistivity data and a sharp specific heat anomaly. The magnetism associated with La$_{5}$Co$_{2}$Ge$_{3}$ is itinerant, has a change in the entropy at $T_\mathrm {C}$ of $\simeq$0.05 R ln2 per mol-Co, and has a low-field saturated moment of $\sim 0.1 \mu_\mathrm B$/Co, making it a rare, itinerant, small moment, low $T_\mathrm C$ compound.