Specific Heat Coefficient Research Articles

Study of Properties of Gold–Iron Alloy in the Macro- and Nanocrystalline States under Different P–T Conditions

Parameters of the Mie–Lennard-Jones pair interatomic potential for a disordered substitutional fcc-Au–Fe alloy are determined. The concentration dependences of the lattice properties of a macrocrystal of this alloy are calculated based on these parameters. The results of calculating twenty properties of fcc-Au, fcc-Fe, and fcc-Au0.5Fe0.5 macrocrystals showed good consistency with the experimental data. The equation of state P(ν, T; N) and baric dependences of both the lattice and surface properties of the fcc-Au0.5Fe0.5 alloy are calculated using the RP nanocrystal model. The calculations have been performed at temperatures T = 100, 300, and 500 K for both the macrocrystal (N = ∞) and the cubic nanocrystal consisting of N = 306 atoms. It is shown that, during isothermal–isobaric (P = 0) decrease in the nanocrystal size, its Debye temperature, elastic modulus, and specific surface energy decrease, while its specific volume, coefficient of thermal expansion, specific heat, and Poisson ratio increase. At low temperatures, the specific surface energy increases in a certain range of pressures with an isothermal–isobaric decrease in the number of atoms in the nanocrystal. This range of pressures disappears with an increase in temperature.

Galerkin finite element analysis of magneto-hydrodynamic natural convection of Cu-water nanoliquid in a baffled U-shaped enclosure

In this paper, single-phase homogeneous nanofluid model is proposed to investigate the natural convection of magneto-hydrodynamic (MHD) flow of Newtonian Cu–H2O nanoliquid in a baffled U-shaped enclosure. The Brinkman model and Wasp model are considered to measure the effective dynamic viscosity and effective thermal conductivity of the nanoliquid correspondingly. Nanoliquid's effective properties such as specific heat, density and thermal expansion coefficient are modeled using mixture theory. The complicated PDS (partial differential system) is treated for numeric solutions via the Galerkin finite element method. The pertinent parameters Hartmann number (1 ≤ Ha ≤ 60), Rayleigh number (103 ≤ Ra ≤ 106) and nanoparticles volume fraction (0% ≤ ϕ ≤ 4%) are taken for the parametric analysis, and it is conducted via streamlines and isotherms. Excellent agreement between numerical results and open literature. It is ascertained that heat transfer rate enhances with Rayleigh number Ra and volume fraction ϕ, however it is diminished for larger Hartmann number Ha.

Piecewise Linear Plastic Potentials as a Tool for Calculating Plane Transient Temperature Stresses

A numerical-analytical solution of a one-dimensional problem of the theory of temperature stresses on the evolution of plane stress states under conditions of heating and subsequent cooling of a round plate made of an elastoplastic material is constructed. The plate is heated in such a way that the level of the bell-shaped temperature distribution increases in proportion to the time up to the set maximum value. After that, the heating source is removed and then cooling occurs in natural conditions. It is shown that following the conditions of piecewise-linear plastic potentials at any calculated time of the deformation process, integration of the equilibrium equation establishes dependences connecting reversible and irreversible deformations and stresses with the temperature distribution. The yield point is assumed to be quadratically dependent on temperature; elastic moduli, specific heat and thermal expansion coefficient are considered constant. It was found that the problem under consideration in the framework of the Tresca-Saint Venant plastic potential has no solution, but it can be solved in the framework of the Ishlinsky – Ivlev plastic potential.

Critical Theory of Non-Fermi Liquid Fixed Point in Multipolar Kondo Problem

When the ground state of a localized ion is a non-Kramers doublet, such localized ions may carry multipolar moments. For example, Pr$^{3+}$ ions in a cubic environment would possess quadrupolar and octupolar, but no magnetic dipole, moments. When such multipolar moments are placed in a metallic host, unusual interactions between these local moments and conduction electrons arise, in contrast to the familiar magnetic dipole interactions in the classic Kondo problem. In this work, we consider the interaction between a single quadrupolar-octupolar local moment and conduction electrons with $p$-orbital symmetry as a concrete model for the multipolar Kondo problem. We show that this model can be written most naturally in the spin-orbital entangled basis of conduction electrons. Using this basis, the perturbative renormalization group (RG) fixed points are readily identified. There are two kinds of fixed points, one for the two-channel Kondo and the other for a novel fixed point. We investigate the nature of the novel fixed point non-perturbatively using non-abelian bosonization, current algebra and conformal field theory approaches. It is shown that the novel fixed point leads to a, previously unidentified, non-Fermi liquid state with entangled spin and orbital degrees of freedom, which shows resistivity $\rho \sim T^{\Delta}$ and diverging specific heat coefficient $C/T \sim T^{-1 + 2\Delta}$ with $\Delta=1/5$. Our results open up the possibility of myriads of non-Fermi liquid states, depending on the choices of multipolar moments and conduction electron orbitals, which would be relevant for many rare-earth metallic systems.

Role of f−d exchange interaction and Kondo scattering in the Nd-doped pyrochlore iridate (Eu1−xNdx)2Ir2O7

We report study of magnetization, resistivity, magnetoresistance and specific heat of the pyrochlore Iridate (Eu1-xNdx)2Ir2O7 with x=0.0, 0.5 and 1.0, where spin orbit coupling, electronic correlation, magnetic frustration and Kondo scattering coexists. Metal insulator transition temperature (T_MI) decrease with increase in Nd content but always coincides with magnetic irreversibility temperature (field induced moment). Resistivity below T_MI do not fit with either activated (gap) or to any power law (gapless) dependence. The Curie constant show surprising result, that Nd induces singlet correlation (reduction of para-moment) in Ir sublattice. Magnetoresistance is negative at low temperatures below 10 K and increases strongly with increase in x and vary quadratically with field switching over to linear dependence above 50 kOe. Low temperature specific heat shows Schottky peak, coming from Nd moments, showing existence of doublet split in Nd energy level, arising from f-d exchange interaction. All materials show presence of a linear specific heat in the insulating region. The coefficient of linear specific heat for x= 0.0 does not vary with external magnetic field but varies superlinearly for x = 1.0 materials. We argue that linear specific heat probably rules out weakly correlated phases like Weyl fermions. We propose that with the introduction of Nd at Eu site the system evolves from chiral spin liquid with gapless spinon excitations with a very small charge gap to Kondo type interaction superposed on chiral spin liquid coexisting with long range antiferromagnetic ordering. Huge increase of magnetoresistance with increase in Nd concentrations shows importance of Kondo scattering in the chiral spin liquid material by rare earth moments.

Channel-selective non-Fermi liquid behavior in the two-channel Kondo lattice model under a magnetic field

Stimulated by anomalous behaviors found in non-Kramers $f$-electron systems in an applied magnetic field, we study a two-channel Kondo lattice model by using a cluster extension of the dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. We include the effect of the external magnetic field in two ways: the Zeeman coupling to conduction electron spins and an effective coupling to the quadrupole degree of freedom through the crystalline electric field splitting. We show that the magnetic field suppresses the antiferroic-spin order (physically, corresponding to the antiferroic-quadrupole order), and yields a channel-selective non-Fermi liquid state where one of the two channels (physically, spin-up or -down) exhibits non-Fermi liquid behavior while the other shows Fermi liquid behavior, before entering the Fermi liquid regime in higher fields. This anomalous state appears in a dome-shaped region which extends from inside the antiferroic-spin ordered phase to the paramagnetic phase. We find that the composite correlation, which is a measure of differentiation in the Kondo coupling between the two channels, is enhanced in this dome-shaped region. We also find that the specific heat coefficient is enhanced in this region in the paramagnetic side, indicating heavy fermion behavior not only in the vicinity of the critical field where the antiferroic-spin order vanishes but also in a certain region of the field and temperature. We discuss the results in comparison with the ordinary Kondo lattice model. We also discuss the implication of our findings to the peculiar behavior observed in the 1-2-20 compounds such as $\rm{PrIr_2Zn_{20}}$, $\rm{PrRh_2Zn_{20}}$, and $\rm{PrV_2Al_{20}}$ under a magnetic field.

Normal-state and superconducting properties of the cubic Laves phase ThIr2

The physical properties of the cubic Laves phase superconductor ThIr2 have been studied by resistivity, magnetic susceptibility and thermodynamic measurements. This compound is found to be a weak coupling type-II superconductor with a Tc of 5.58 K and a fully isotropic superconducting gap. The electronic specific heat coefficient, upper critical field and Ginzburg-Laudau parameter are determined to be 13.1 mJ mol−1 K−2, 2.25 T, and 20.4, respectively. In the normal state, the susceptibility follows a Curie-Weiss behavior with a paramagnetic moment of 0.46 μB per f.u.. Furthermore, the low-temperature resistivity exhibits a quadratic temperature dependence, yielding a large Kadowaki-Woods ratio of 7.6×10−5μΩ cm/(mJ mol−1 K−1)2. This, together with a Wilson ratio of ~1.4, suggests the importance of electronic correlation in ThIr2. First-principles calculations show that the valence band states below the Fermi level are dominated by the Ir-5d orbitals, yet significant hybridizations with the Ir-6p, Th-6d, 7p orbits are detected at the Fermi level. The inclusion of spin-orbit coupling has little influence on the Fermi surface shape but lowers the density of states toward the experimental value. A comparison with isostructural CaIr2 and SrIr2 is also presented.

Equation of State of CO_{2} Shock Compressed to 1TPa.

Equation-of-state (pressure, density, temperature, internal energy) and reflectivity measurements on shock-compressed CO_{2} at and above the insulating-to-conducting transition reveal new insight into the chemistry of simple molecular systems in the warm-dense-matter regime. CO_{2} samples were precompressed in diamond-anvil cells to tune the initial densities from 1.35 g/cm^{3} (liquid) to 1.74 g/cm^{3} (solid) at room temperature and were then shock compressed up to 1 TPa and 93 000K. Variation in initial density was leveraged to infer thermodynamic derivatives including specific heat and Gruneisen coefficient, exposing a complex bonded and moderately ionized state at the most extreme conditions studied.

Comparative experimental study of the dynamic properties and adiabatic shear susceptibility of titanium alloys

Titanium and titanium alloys are prone to adiabatic shear failure when deformed at high strain rates due to their low coefficients of specific heat and thermal conductivity. Comparative study of the adiabatic shear susceptibility of titanium alloys are seldom reported in the literature. To further understand this topic, the mechanical response of five representative titanium alloys, i.e. commercially pure titanium (TA2, α), Ti-6.5Al–2Zr–1Mo–1V (TA15, near α), commercially Ti–6Al–4V (TC4, α+β), Ti–5Al–5Mo–5V–1Cr–1Fe (TC18, near β) and Ti–3Al–8V–6Cr–4Mo–4Zr (TB9, β), is characterized over a wide range of strain rates (ranging from 0.001 to 4000s−1) and temperatures (ranging from 293 to 673K). The findings of this experimental demonstrate that the yield stress of TA2 is the lowest, while it is the highest for TC18. The strain hardening effect of titanium alloys is prominent at low strain rate, while it may be decreased at high strain rates due to the presence of β-phase stabilizers. In addition, the mechanical behavior of titanium alloys is sensitive to strain rate and test temperature. The results also suggest that the formation of ASB is related to the applied strain rate and initial test temperature, and higher test temperature and strain rate promote the occurrence of adiabatic shear localization in dynamic deformation. Moreover, for titanium alloys, a lower strain-hardening coefficient and higher strength does not correspond to high sensitivity to adiabatic shear failure, and the dynamic failure energy, with its constant value, seems to be the best indicator of ASB failure. Furthermore, our results and analysis are important in enhancing the understanding of the dynamic properties and adiabatic shear susceptibility of titanium alloys. Based on this work, engineers can choose the optimal titanium alloy to fabricate components according to the service requirements to fully utilize the potential of the material.

Specific Heat and Thermal Expansion Coefficient of Hybrid Epoxy Composites

Thermal behavior of hybrid epoxy composites reinforced with different types of plain weave fabrics and ply orientation at various angles was investigated in this research. It was analyzed their thermal linear expansion coefficient and specific heat measured with Thermomechanical Analyzer (TMA) and Differential Scanning Calorimeter (DSC) respectively. Also, in this paper was studied the influence of carbon black - aramid powder and carbon black - barium ferrite mixtures added into epoxy matrix between certain plies of the hybrid composites. The experimental results showed that the addition of filler mixtures led to a significant decreasing of thermal expansion coefficient and specific heat of the hybrid epoxy composite with carbon outer plies. It was recorded a good structural stability in case of hybrid carbon-glass composite in the temperature range of 40-60�C.

An Analysis on some thermal characteristics of AlMg10-SiC ultralight composite materials

The paper presents the determination of the specific heat, thermal conductivity and thermal expansion coefficients of some composites of the type AlMg10-SiC with the help of a differential scanning calorimeter. For the experiment we will use several types of composites with different concentrations of SiC (5%, 10%, 15%, with 120 micrometres medium size).One sample category was obtained by melt bubbling method (A) and the other one by soluble salt method (B). We obtained cellular composites using A method and porous composites using B method. The paper presents by comparison the thermal properties of the two categories of materials. The paper also presents the equipment used, as well as its operation. We used a differential scanning calorimeter for the specific heat and thermal conductivity determinations and thermomechanical analyser equipment for linear expansion coefficients. Based on the values obtained for the thermal characteristics of the investigated composite materials, those directions of applications can be suggested, which can be based on the absorption characteristics of the deformation energy of these composites, even at temperatures above 100°C, a situation for which, for example, in general, polymeric composites cannot be used.

Multigap superconductivity in the Mo5PB2 boron–phosphorus compound

The tetragonal Mo5PB2 compound was recently reported to show superconductivity with a critical temperature up to 9.2 K. In search of evidence for multiple superconducting gaps in Mo5PB2, comprehensive measurements, including magnetic susceptibility, electrical resistivity, heat capacity, and muon-spin rotation and relaxation measurements were carried out. Data from both low-temperature superfluid density and electronic specific heat suggest a nodeless superconducting ground state in Mo5PB2. Two superconducting energy gaps Δ0 = 1.02 meV (25%) and 1.49 meV (75%) are required to describe the low-T electronic specific-heat data. The multigap features are clearly evidenced by the field dependence of the electronic specific-heat coefficient and the Gaussian relaxation rate in the superconducting state (i.e., superfluid density), as well as by the temperature dependence of the upper critical field. By combining our extensive experimental results with numerical band-structure calculations, we provide compelling evidence of multigap superconductivity in Mo5PB2.

Magnetic and magnetothermal properties of Gd75Cu25 prepared by melt-spinning

Magnetic and magnetothermal properties of melt-spun Gd75Cu25 alloy were studied. A second-order magnetic phase transition is observed at the Curie temperature of 144 K. The peak value of the magnetic entropy change −ΔSmpk = 7.0 J kg−1 K−1 is observed near the Curie point under the magnetic field change 0–5 T, while the refrigerant capacity is found to be 594 J kg−1. The specific heat exhibits a wide transition near the Curie temperature, and the non-magnetic contributions to the total specific heat are described using the Debye temperature ΘD = 155 K and the electronic specific heat coefficient γ = 65 mJ mol−1 K−2.

Aqueous nanofluids containing paraffin-filled MWCNTs for improving effective specific heat and extinction coefficient

This paper presents measurements of the effective specific heat and the extinction coefficient for aqueous nanofluids dispersed with paraffin-filled Multi-Walled Carbon NanoTubes (MWCNTs). The MWCNTs were filled with paraffin wax by capillary action. Centrifugal decanting was used to modify the traditional two-step method so as to produce a nanofluid dispersion that was more stable than that produced by the traditional method. The stability of each suspension was quantitatively evaluated with a laser scattering method over 7 days. A differential scanning calorimetry (DSC) and the three-slap method were used to measure the effective specific heat and the extinction coefficient of the nanofluids, respectively. The measured effective specific heat of the water-based paraffin-filled MWCNTs nanofluid, with a volume fraction of 1%, was up to 5.1% larger than that for the water-based MWCNT nanofluids without paraffin wax. The nanofluid extinction coefficient was shown to increase linearly with the volume fraction for data within the independent scattering regime, which occurred when the nanoparticle-distance/wavelength ratio (c/λ) was less than 2.

Thermal property measurements of metal injection moulded Inconel 625 and Inconel 718 using combined thermal analysis techniques

ABSTRACT The high-temperature thermal properties of powder metallurgy derived superalloys have not been reported in the literature. In this study, the coefficient of thermal expansion (CTE), specific heat and thermal diffusivity of metal injection moulded (MIM) Inconel 625 and Inconel 718 were measured. Measurements of wrought Nickel 200 were also made to verify the methods. These thermal property measurements were made in the range of room temperature to 1000–1200°C using dilatometry, differential scanning calorimetry and laser flash analysis. Thermal conductivity of all three materials was calculated using the measured diffusivity, specific heat and CTE. All the MIM results were compared to published data for the wrought form of these alloys and found to be in close agreement outside of phase transition regions.

Phase stability, mechanical, electronic, magnetic and optical properties of tetragonal and cubic M3V (M: Pd, Pt) structures

The full potential linearized augmented plane wave (FP-LAPW) method was used to investigate the ground states as well as the mechanical, electronic, magnetic and optical properties of M3V (M: Pd, Pt) compounds. The generalized gradient approximation (GGA) of Perdew-Burke and Ernzerhof (PBE-GGA) is employed to treat the exchange-correlation potential for all the calculations except for structural properties where both Wu and Cohen generalized gradient approximation (WC-GGA) and Perdew and Wang local spin density approximation (LSDA) have been added. The cohesive energies, the formation enthalpies and the densities of states at the Fermi level N(EF) show that the D022 structure is more stable than D023 and L12. The lattice parameter and bulk modulus results agree well with the available experimental measurements and theoretical predictions. The elastic and mechanical properties are predicted and show that both compounds exhibit ductile behavior. Furthermore, our calculations of Debye and melting temperatures are in good agreements with experimental results reported in the literature. The densities of states (DOS) show that strong d-d hybridization is behind the formation of the pseudogap at the Fermi level. The contours of the valence charge densities show combinations of metallic and covalent bonds. The number of bonding electrons per atom nb, the electronic specific heat coefficient γ, and the electron-phonon coupling constant λ, are determined. The obtained values of the magnetic moments and polarization coincide with the reported values for both D022 and L12 structures. Moreover, the optical properties, including the dielectric functions, extinction coefficient K(ω), reflectivity coefficient R(ω) and energy loss function L(ω) are studied in the range of 0–14 eV.

Low temperature specific heat of 12442-type KCa2Fe4As4F2 single crystals

Low-temperature specific heat (SH) is measured for the 12442-type KCa$_2$Fe$_4$As$_4$F$_2$ single crystal under different magnetic fields. A clear SH jump with the height of $\Delta C/T|_{T_c}$ = 130 mJ/mol K$^2$ is observed at the superconducting transition temperature $T_c$. It is found that the electronic SH coefficient $\Delta\gamma (H)$ quickly increases when the field is in the low-field region below 3 T and then considerably slows down the increase with a further increase in the field, which indicates a rather strong anisotropy or multi-gap feature with a small minimum in the superconducting gap(s). The temperature-dependent SH data indicates the presence of the $T^2$ term, which supplies further information and supports the picture with a line-nodal gap structure. Moreover, the onset point of the SH transition remains almost unchanged under the field as high as 9 T, which is similar to that observed in cuprates, and placed this system in the middle between the BCS limit and the Bose-Einstein condensation.

Intermediate Valence Behavior of Yb2Cu9Al8

Intermediate valence behavior is frequently observed in materials containing Ce, Yb, Eu, Sm, or Tm. In the current work, we report synthesis and characterization of Yb2Cu9Al8 (Th2Zn17 structure type). Its intermediate valence behavior can be described by an excitation energy Eex/kB = 319 K and a spin fluctuation temperature Tsf = 60 K. The valence state of Yb is estimated to be close to 2.04 for the low‐temperature region. The valence gradually evolves to the value of 2.80 at T = 400 K. The specific heat coefficient of γexp = 59 mJ·molYb–1·K–2 indicates a moderate effective mass enhancement, together with finite density of states at the Fermi level. The latter is also confirmed by the band structure calculations.

Metal-to-metal transition and heavy-electron state in Nd4Ni3O10−δ

The trilayer nickelate ${\mathrm{Nd}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10\ensuremath{-}\ensuremath{\delta}}$ was investigated by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility, and heat capacity. The crystal structure data suggest a higher Ni valence in the inner perovskitelike layer. At ambient pressure the resistivity shows a jump at 162 K, indicating a metal-to-metal transition (MMT). The MMT is also characterized by a magnetic susceptibility drop, a sharp specific-heat peak, and an isotropic lattice contraction. Below $\ensuremath{\sim}50\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, a resistivity upturn with $logT$ dependence shows up, accompanied with negative thermal expansion. External hydrostatic pressure suppresses the resistivity jump progressively, coincident with the weakening of the $logT$ behavior. The low-temperature electronic specific-heat coefficient is extracted to be $\ensuremath{\sim}150\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{mol}\text{\ensuremath{-}}{\mathrm{f}.\mathrm{u}.}^{\ensuremath{-}1}$, equivalent to $\ensuremath{\sim}50\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{mol}\text{\ensuremath{-}}{\mathrm{Ni}}^{\ensuremath{-}1}$, indicating an unusual heavy-electron correlated state. The novel heavy-electron state as well as the logarithmic temperature dependence of resistivity is explained in terms of the ${\mathrm{Ni}}^{3+}$-centered Kondo effect in the inner layer of the ${({\mathrm{NdNiO}}_{3})}_{3}$ trilayers.

Quantum Criticality of Valence Transition for the Unique Electronic State of Antiferromagnetic Compound EuCu2Ge2

The effect of pressure on the unique electronic state of the antiferromagnetic (AF) compound EuCu2Ge2 has been measured in a wide temperature range from 10 mK to 300 K by electrical resistivity measurements up to 10 GPa. The Neel temperature of TN = 15 K at ambient pressure increases monotonically with increasing pressure and becomes a maximum of TN = 27 K at 6.2 GPa but suddenly drops to zero at Pc = 6.5 GPa, suggesting the quantum critical point (QCP) of the valence transition of Eu from a nearly divalent state to that with trivalent weight. The rhomag0 and A values obtained from the low-temperature electrical resistivity based on the Fermi liquid relation of rhomag = rhomag0 + AT^2 exhibit huge and sharp peaks around Pc. The exponent n obtained from the power law dependence rhomag = rhomag0 + BT^n is clearly less than 1.5 at P = Pc = 6. 5 GPa, which is expected at the AF-QCP. These results indicate that Pc coincides with Pv, corresponding to the quantum criticality of the valence transition pressure Pv. The electronic specific heat coefficient, estimated from the generalized Kadowaki-Woods relation, is about 510 mJ/mol K^2 around Pc, suggesting the formation of a heavy-fermion state.