Low-temperature Thermodynamic Properties Research Articles

The Modified Debye–Grüneisen Model for Highly Compressed Diamond

A new modification of the Debye–Gruneisen model is proposed. It takes explicitly into account the anharmonicity of phonon modes, which leads to the nonlinear dependence of energy levels on quantum numbers. The low-temperature version of this model considering anharmonic displacement of only the lowest energy levels of both longitudinal and transverse phonons is developed. This model, calibrated on results of DFT ab initio calculations, reproduces all predicted low-temperature thermodynamic properties of diamond at pressures up to 1 TPa, including the region of its negative thermal expansion.

Thermodynamic Investigation of Metamagnetic Transitions and Partial Disorder in the Quasi-Kagome Kondo Lattice CePdAl

Low-temperature ($T$) thermodynamic properties in magnetic fields ($B$) of the quasi-Kagome antiferromagnet CePdAl ($T_{\rm N}\sim$ 2.7 K) were studied by means of magnetization and specific-heat $C(T,B)$ measurements. The unusual magnetic phase diagram, including three thermodynamic phases I-III, and crossover anomalies, has been obtained. In low-field phase I, the existence of the partial Kondo screening state on the one-third Ce sites is supported from the thermodynamic point of view: (i) an appearance of the paramagnetic moment with one-third of the full moment around 3 T, and (ii) an occurrence of the entropy release $\sim$0.3$R$ln2 around the observed crossover. On the other hand, a strong enhancement of $C/T$ is found around the point, where $T_{\rm N}(B)$ meets the boundary of phase III, indicating the possible presence of a tri-critical point. Furthermore, it is suggested that the three metamagnetic transitions at $B_{{\rm m}i}$ ($i=$1,2,3) come from successive increments of the Ising-type magnetic moment along the $c$-axis. In high-field state above 20 T, the behavior of $f$ electron can be rather described by the crystal-electric-field model.

Low-temperature molar heat capacities, thermodynamic properties and crystal structure of Cu(C3N2H4)4(ClO4)2

A complex of copper perchlorate coordinated with imidazole Cu(C3N2H4)4(ClO4)2 was synthesized and characterized by X-ray single-crystal diffraction. The complex is centrosymmetric in the monoclinic P2(1)/c space group. The low-temperature molar heat capacities and thermodynamic properties of the complex were studied with adiabatic calorimetry (AC). The thermodynamic functions [H T–H 298.15] and [S T–S 298.15] were derived in the temperature range from 80 to 370 K with temperature interval of 5 K. Thermal decomposition behavior of the complex in nitrogen atmosphere was studied by thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). The mechanism of the decomposition was deduced to be the breaking up the two Cl–O bonds of the Cl–O–Cu and the Cu–N bonds of the imidazole rings in succession.

Ground-state candidate for the classical dipolar kagome Ising antiferromagnet

We have investigated the low-temperature thermodynamic properties of the dipolar kagome Ising antiferromagnet using at-equilibrium Monte Carlo simulations, in the quest for the ground-state manifold. In spite of the limitations of a single spin-flip approach, we managed to identify certain ordering patterns in the low-temperature regime and we propose a candidate for this unknown state. This novel configuration presents some intriguing features and passes several test-criteria, making it a very likely choice for the dipolar long-range order of this kagome Ising antiferromagnet.

Thermodynamics of the d-wave pairing in organic superconductors

Organic superconductors with [Formula: see text]-type structure are most frequently identified as nodal gap superconductors from the experimental observation of a power-law behavior in the low-temperature thermodynamic properties such as specific heat capacity. We perform series of theoretical calculations of specific heat capacity of three typical organic complexes with different transition temperatures by using Bogolyubov–de Gennes equations. The good agreement between the experimental data and the calculations demonstrates that the [Formula: see text]-wave pairing is certainly realized in these superconductors.

Quantum Critical Behavior in a Concentrated Ternary Solid Solution.

The face centered cubic (fcc) alloy NiCoCrx with x ≈ 1 is found to be close to the Cr concentration where the ferromagnetic transition temperature, Tc, goes to 0. Near this composition these alloys exhibit a resistivity linear in temperature to 2 K, a linear magnetoresistance, an excess –TlnT (or power law) contribution to the low temperature heat capacity, and excess low temperature entropy. All of the low temperature electrical, magnetic and thermodynamic properties of the alloys with compositions near x ≈ 1 are not typical of a Fermi liquid and suggest strong magnetic fluctuations associated with a quantum critical region. The limit of extreme chemical disorder in this simple fcc material thus provides a novel and unique platform to study quantum critical behavior in a highly tunable system.

Low-temperature molar heat capacities and thermodynamic properties of a new rare earth complex Er2(μ 2-Gly)6(H2O)4·Na2(ClO4)8(H2O)2·4H2O

A hydrous complex of erbium coordinated with glycine sodium perchloric acid, Er2(μ 2-Gly)6(H2O)4·Na2(ClO4)8(H2O)2·4H2O (Gly = glycine), was synthesized firstly and characterized by X-ray single-crystal diffraction. The complex crystallizes centrosymmetrically in the triclinic P-1 space group [a = 9.2959 (5), b = 12.1756 (7) A, c = 13.9928 (7) A, V = 1367.67 (13) A3, Z = 1]. The low-temperature molar heat capacities and thermodynamic properties of the complex were studied with adiabatic calorimetry. The thermodynamic functions, [H T–H 298.15] and [S T–S 298.15], were derived in the temperature range from 80 to 370 K with a temperature interval of 5 K. Thermal decomposition behavior of the complex in nitrogen atmosphere was studied by thermogravimetric analysis and differential scanning calorimetry.

Low-temperature heat capacity and thermodynamic properties of PrPO4

The heat capacity of praseodymium orthophosphate PrPO4 was measured by adiabatic and relaxation calorimetric techniques at 5.12–345.54 K, and these data were utilized to calculate thermodynamic functions of PrPO4 at 6–350 K. The Gibbs free energy of PrPO4 formation Δ f G 0(298.15 K) is evaluated at 1851.8 ± 4.7 kJ mol–1.

A study of mechanical properties of multi-layered graphene using modified Nosé–Hoover based molecular dynamics

The modified Nosé–Hoover (NH) thermostat incorporated with molecular dynamics calculation is applied to evaluate the mechanical properties of multi-layered graphene structures at atmospheric pressure, including Young’s modulus, shear modulus, Poisson’s ratio, specific heats, linear coefficient of thermal expansion (CTE) and thermal conductivity. The thermostat method takes into account the contribution of phonons by virtue of the vibrational energy of the lattice and the zero-point energy, thereby providing a better prediction of the low temperature thermodynamic properties. The focuses of this study are placed on exploring their temperature, size, chirality and layer number dependences. The validity of the calculations is further demonstrated by comparing the calculated results with those derived from the existing thermostats, namely, the standard NH, Nosé–Hoover chain (NHC), “massive” NHC and velocity-rescaling thermostats, and also with the literature experimental and theoretical data.It was found that the calculated mechanical properties of the graphene sheets agree well with the published experimental and theoretical results. The results also show that their Young’s modulus, shear modulus, linear CTE and Poisson’s ratio tend to decrease with the increase of temperature, size and layer number, where the linear CTE would eventually converge to that of the bulk graphite. Besides, the heat capacity and thermal conductivity at low temperatures show the high temperature dependences, i.e., the third and λ (λ=2–3) power of temperature, which are more consistent with that obtained from Debye model.

Low temperature transport and thermodynamic properties of the Zintl compound Yb11AlSb9: A new Kondo lattice semiconductor

A thorough transport and thermodynamic investigation of flux-grown single crystals of the ternary Zintl phase Yb11 AlSb9, combined with first-principles density functional theory calculations, shows that this compound is a metal above T ≈ 100 K and a semiconductor with small hybridization gap at low-T. The general behavior resembles those of Kondo lattice semiconductors, although some of the measured properties are strongly sample dependent, as often seen in hybridized f-electron materials. We thus suggest that Yb11 AlSb9 can be considered as a new Yb-based Kondo lattice semiconductor joining the family of strongly correlated electron systems.

Low-Temperature Heat Capacities and Thermodynamic Properties of 2-Aminopyridine

Low-Temperature Heat Capacities and Thermodynamic Properties of 2-Aminopyridine

Topological Weyl superconductor to diffusive thermal Hall metal crossover in theBphase ofUPt3

The recent phase sensitive measurements in the superconducting $B$-phase of UPt$_3$ provide strong evidence for the triplet, chiral $k_z(k_x \pm ik_y)^2$ pairing symmetries, which endow the Cooper pairs with orbital angular momentum projections $L _z= \pm 2$ along the $c$-axis. In the absence of disorder such pairing can support both line and point nodes, and both types of nodal quasiparticles exhibit nontrivial topology in the momentum space. The point nodes, located at the intersections of the closed Fermi surfaces with the $c$-axis, act as the double monopoles and the antimonopoles of the Berry curvature, and generalize the notion of Weyl quasiparticles. Consequently, the $B$ phase should support an anomalous thermal Hall effect, the polar Kerr effect, in addition to the protected Fermi arcs on the (1,0,0) and the (0,1,0) surfaces. The line node at the Fermi surface equator acts as a vortex loop in the momentum space and gives rise to the zero energy, dispersionless Andreev bound states on the (0,0,1) surface. At the transition from the $B$-phase to the $A$-phase, the time reversal symmetry is restored, and only the line node survives inside the $A$-phase. As both line and double-Weyl point nodes possess linearly vanishing density of states, we show that weak disorder acts as a marginally relevant perturbation. Consequently, an infinitesimal amount of disorder destroys the ballistic quasiparticle pole, while giving rise to a diffusive phase with a finite density of states at the zero energy. The resulting diffusive phase exhibits $T$-linear specific heat, and an anomalous thermal Hall effect. We predict that the low temperature thermodynamic and transport properties display a crossover between a ballistic thermal Hall semimetal and a diffusive thermal Hall metal.

Delta chain with anisotropic ferromagnetic and antiferromagnetic interactions

We consider analytically and numerically an anisotropic $\text{spin}\ensuremath{-}\frac{1}{2}$ delta chain (sawtooth chain) with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interactions. For certain values of the interactions a lowest one-particle band becomes flat and there is a class of localized-magnon eigenstates which form a ground state with a macroscopic degeneracy. In this case the model depends on a single parameter which can be chosen as the anisotropy of the exchange interactions. When this parameter changes from zero to infinity the model interpolates between the one-dimensional isotropic ferromagnet and the frustrated Ising model on the delta chain. It is shown that the low-temperature thermodynamic properties in these limiting cases are governed by the specific structure of the excitation spectrum. In particular, the specific heat has one or infinite number of low-temperature maxima for the small or the large anisotropy parameter, correspondingly. Qualitative features of such behavior survive when the interaction parameters deviate from the relations providing the local magnon ground state.

Low-temperature molar heat capacity and thermodynamic properties of rare earth complex

A heptanuclear trigonal prismatic polyhedron, [EuCu6(μ-OH)3(Gly)6Im6](ClO4)6·3H2O, was synthesized and characterized by elemental analysis and X-ray single-crystal diffraction. The complex crystallize is the rhombohedral R3 space group (a = b = 15.8673 A, c = 23.4038 A, V = 5103.0(6) A3, Z = 3). In the clusters, Eu3+ ions are situated in the center of a prism formed by six copper atoms and coordinate to nine oxygen atoms with a tricapped trigonal prismatic coordination polyhedron. Six glycinato ligands and six imidazole terminal ligands (each coordinates to one Cu2+) were used in the construction of the cluster. The low-temperature molar heat capacity, C p,m, and thermodynamic properties of the complex were studied with an adiabatic calorimeter from 80 to 370 K. The thermodynamic functions [H T–H 298.15] and [S T–S 298.15] were derived in the temperature range from 80 to 370 K with a temperature interval of 5 K. The thermal properties of the complex from 300 to 800 K were studied by DSC and TG in nitrogen atmosphere.

Low-temperature heat capacities and thermodynamic properties of ethyl 4-dimethylaminobenzoate (C11H15NO2)

Molar heat capacities of ethyl 4-dimethylaminobenzoate were measured by a high precision automated adiabatic calorimeter over the temperature range from 79 to 397 K. The melting temperature, the molar enthalpy and entropy of fusion were determined to be (336.818 ± 0.017) K, (20.761 ± 0.345) kJ mol−1 and (61.64 ± 1.03) J K−1 mol−1. It has a great potential in the use of the substance as solid–liquid phase change material based on large enthalpy of solid–liquid phase transition and moderate melting temperature. The thermodynamic functions (HT−H298.15 K) and (ST−S298.15 K) were calculated in the temperature range from 80 to 400 K with the interval of 5 K. The mass fraction purity of the sample was determined to be (1−N) = 0.99514 (mol fraction) by the fractional melting method. The constant-volume energy and standard molar enthalpy of combustion were determined, ΔcU (C11H15NO2, s) = −(6,161.73 ± 5.19) kJ mol−1 and Δc\( H_{\text{m}}^{0} \) (C11H15NO2, s) = −(6,167.31 ± 5.19) kJ mol−1, by means of a precision oxygen-bomb combustion calorimeter at T = 298.15 K. At last, the standard molar enthalpy of formation was derived, Δf\( H_{\text{m}}^{0} \) (C11H15NO2, s) = −(305.03 ± 6.92) kJ mol−1.

Comprehensive Study of the Low-Temperature Transport and Thermodynamic Properties of the Cluster Compounds AgxMo9Se11 (3.41 ≤ x ≤ 3.78)

We present a detailed study of the evolution of the electrical, galvanomagnetic, and thermodynamic properties of polycrystalline AgxMo9Se11 compounds for 3.4 ≤ x ≤ 3.8 at low temperatures (2–350 K). In agreement with density functional theory calculations, the collected data show an overall gradual variation in the transport properties from metallic to semiconducting behavior on going from x = 3.4 to 3.8. The results evidence subtle variations in the electronic properties with the Ag content, typified by both positive and negative phonon-drag effects together with thermopower and Hall coefficient of opposite signs. Analysis of the data suggests that these features may be due to peculiarities of the dispersion of the valence bands in the vicinity of the chemical potential. A drastic influence of the Ag content on the thermal transport was evidenced by a pronounced change in the temperature dependence of the specific heat below 10 K. Nonlinearities in the Cp(T3) data are correlated to the concentration of Ag atoms, with an increase in x resulting in a more pronounced departure from a Debye law. The observed behavior mirrors that of ionic conductors, suggesting that AgxMo9Se11 for x ≥ 3.6 might belong to this class of compounds.

Ab initio thermodynamics of zirconium hydrides and deuterides

We report the results of a systematic ab initio study of the elastic and thermodynamic properties of γ-ZrH, δ-ZrH1.5,γ-ZrD, and δ-ZrD1.5. In addition, pure α-Zr as well as the ε-ZrH2 and ε-ZrD2 phases are evaluated for reference. The calculations are performed using quantum mechanical density functional theory (DFT) with the frozen core projector augmented wave (PAW) approach and a generalised gradient approximated (GGA) exchange–correlation functional. To capture the variations of the thermodynamic quantities over a wide range of temperatures (0≲T⩽1000K), the quasi-harmonic approximation approach is adopted where the influence of the vibrational and electronic free energies are included by means of the phonon and electron densities of state. This allows for quantifying the contributions of the electron density of states, which were not accounted for in the previous studies. All the pertinent elastic constants and phonon properties for the considered hydride/deuteride phases are calculated and compared with experimental data; which were not done before. We have further computed the entropy, heat capacity and enthalpy as well as low temperature thermodynamic properties such as the Debye temperature and the electronic heat capacity constant for all the hydride and deuteride phases. The results of our computations concur well with the corresponding data obtained by measurements that are reported in the literature and offer the necessary data and basis for multiscale modelling of zirconium alloys.

Anomalous thermodynamic power laws near topological transitions in nodal superconductors

Unconventional superconductors are most frequently identified by the observation of power-law behaviour on low-temperature thermodynamic or transport properties, such as specific heat. Here we show that, in addition to the usual point and line nodes, a much wider class of different nodal types can occur. These new types of nodes typically occur when there are transitions between different types of gap node topology, for example when point or line nodes first appear as a function of some physical parameter. We identify anomalous, non-integer thermodynamic power laws associated with these new nodal types, and give physical examples of superconductors in which they might be observed experimentally, including the noncentrosymmetric superconductor Li$_2$Pd$_{3-x}$Pt$_x$B.

Low-temperature properties of an integrable spin-3/2 gas with weak external magnetic field

We study the low-temperature thermodynamic properties of an integrable spin-3/2 fermionic model. Many interesting kinds of fermionic pairs exist in the systems. By using the Wiener-Hopf method, we obtain the ground state and the equation of state at low temperatures. The ground-state energy without binding energy and Zeeman energy can be represented by the spinless free fermions with an effective mass and a quadratic correction of the weak external magnetic field. We also discuss the quantum criticality for the phase transition from vacuum state to the super Tonks-Girardeau-like phase near the strong coupling limit.

CALPHAD description of the Mo–Re system focused on the sigma phase modeling

Abstract The phase equilibria and thermodynamic properties of the Mo–Re system are studied by combining first-principle and CALPHAD approach. The mixing enthalpies in the bcc and hcp solution phases are estimated by first-principle calculations using the special quasirandom structures. The liquid, bcc and hcp phases are described by a substitutional solution model. The intermetallic phases, σ and χ , are described with the compound energy formalism with, respectively, 5 and 4 sublattices (SL) using the formation enthalpies of all the end-members directly from ab initio calculations. A phase diagram in agreement with the available experimental knowledge is obtained thanks to a least square procedure involving a limited number of parameters. Introducing all the elements in all the sublattices of the structure allows a proper description of the configuration of the intermetallic phases. Different simplifications of the description of the σ phase are considered. The ideal 4SL simplification is equivalent to the full description. The 3SL and 2SL models require excess parameters in order to fit reasonably the experimental phase diagram. Among these, only the (Mo,Re) 10 (Mo,Re) 12 (Mo,Re) 8 model allows to closely approximate the low temperature thermodynamic properties of the full description.