The specific heat of high quality La^{N}B_{6} (N=10, 11, natural) single crystals is investigated in a wide range of temperatures 2 - 300 K. The obtained data allow to estimate correctly (i) the electronic γ· T term of specific heat (γ ≈ 2.4 mJ/(mol·K^{2})), (ii) the contribution from quasilocal vibrating mode of La^{3+} ions (Θ_{E} ≈ 150 - 152 K), (iii) the Debye-type term from rigid boron cages (Θ_{D} ≈ 1160± 40 K). Our data also suggest an additional defect-mode component (iv) which may be attributed to a contribution of 1.5% boron vacancies in LaB_{6}. The obtained results may be interpreted in terms of formation of two level systems, which appear when La^{3+} ions are displaced from their centrosymmetric positions in the cavities of rigid boron cages, apart from randomly distributed boron vacancies in the LaB_{6} matrix.
We present the detailed study of magnetic, thermodynamic, and transport properties of polycrystalline NdAgAl₃. The compound crystallizes in BaNiSn₃-type tetragonal structure with the space group I4mm. Magnetic, heat capacity and transport measurements indicate the possible antiferromagnetic nature of the ordering below 2 K. The compound shows the Schottky anomaly in heat capacity data. Magnetoresistance is negative at low temperature.
Here we present the results of the zero-field specific heat study of the LuFe_6Al_6 single crystal. The specific heat data were analyzed as a sum of the phonon, electronic, and magnetic contributions, respectively. The analysis of the phonon part involves three acoustic and 36 optical branches, respectively, all of them corrected for the anharmonicity. The magnetic part of the specific heat was obtained by subtracting the electronic and the phonon part from the experimental specific heat and the magnetic entropy was calculated.
We present analysis of the specific heat of the RTAl (R = Y, Lu;T = Cu, Ni, Pd) compounds. We focus on the lattice contribution and analyze the dependence of all the characteristic parameters in the Debye and Einstein models on the atomic masses and interatomic distances.
We have investigated the structural, elastic, electronic, optical and thermal properties of CsBaF₃ perovskite using the full-potential linearized augmented plane wave method within the generalized gradient approximation and the local density approximation. Moreover, the modified Becke-Johnson potential (TB-mBJ) was also applied to improve the electronic band structure calculations. The ground state properties such as lattice parameter, bulk modulus and its pressure derivative were calculated and the results are compared with the available theoretical data. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young's modulus and Poisson's ratio are obtained for the first time. Electronic and bonding properties are discussed from the calculations of band structure, density of states and electron charge density. The contribution of the different bands was analyzed from the total and partial density of states curves. The different interband transitions have been determined from the imaginary part of the dielectric function. The thermal effect on the volume, bulk modulus, heat capacities C_V and the Debye temperature was predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account.
The heat capacity in the applied magnetic field up to 9 T, susceptibility and magnetization of polycrystalline CeCu_{4}Ga are presented. Magnetic ordering was not observed down to 2 K. For temperature T < 200 K a Curie-Weiss behavior is observable giving an effective magnetic moment μ_{eff} =2.53 μ_{B}/f.u. The experimental value of μ_{eff} is close to the calculated one for a free Ce^{3+} ion (μ_{eff} = 2.54 μ_{B}/f.u.), thus indicating the presence of well localized magnetic moments carried by the stable Ce^{3+} ions. At low temperatures the electronic heat capacity coefficient value depends strongly on the temperature range used for the extrapolation and applied magnetic field. We observe a typical heavy fermion behavior with γ value of about 380 mJ mol^{-1} K^{-2} obtained from extrapolation to T = 0 K of the temperature range above 7 K. However, extrapolation of the lowest temperatures range yields the γ value of 3.3 J mol^{-1} K^{-2}.
An antiferromagnetic order with a Néel temperature T_{N} = 17.5 K, a strong ferromagnetic exchange evidenced by a positive Curie-Weiss temperature θ_{CW} = 77.3 K, the fuzzy peaks in the real component of susceptibility χ'(T) and the disappearance of the second critical field were established. The curvature of specific heat C(T) and C(T)/T in surrounding of T_{N} indicated a broad peak, characteristic for the system with inhomogeneous magnetic state (spin-glass-like phase). The calculated magnetic entropy showed the value of S(T) ≈ 1 J/(mol K) which is extremely small; i.e., much lower than the magnetic contribution Rln(2S + 1) = 11.52 J/(mol K) calculated for the spin 3/2.
The structural, elastic, thermodynamic and electronic properties of nonmetallic metal FeCrAs are studied within density function perturbation theory. The thermodynamic properties of FeCrAs were deduced based on phonon frequencies within the framework of the quasiharmonic approximation. The calculated elastic modulus under various pressures indicates that FeCrAs is mechanically stable under pressure. The pressure-dependence of bulk and shear modulus, transverse and longitudinal sound velocities V (i.e. V_{S} and V_{L}), elastic Debye temperature Θ_{E} of FeCrAs have also been investigated. The calculated values of B/G indicate that FeCrAs presents high ductility under pressure. However, it is interesting that the value of B/G reaches a maximum under 40 GPa and almost remains unchanged when the pressure is above 70 GPa. The calculations show that the heat capacity C_{V} of this material is close to the Dulong-Petit limit 3R (about 224.61 J mol^{-1} K^{-1}) at high temperature regime. The analysis of electronic properties find that as the pressure increases, the absolute value of charge for As and Fe atom increases while Cr remains nearly a constant, indicating that the mechanic properties of FeCrAs under pressure should be mostly attributed to the interaction between Fe and As atoms.
This paper presents the results of investigations of the temperature dependence of heat capacity and dielectric dispersion in the vicinity of ferroelectric-ferroelastic phase transition of dimethylammonium metal sulphate hexahydrate crystals DMAAl_{1-x}Cr_{x}S. In particular, it is shown that the isomorphous substitution of metal ion noticeably changes the temperature of phase transition and parameters of the fundamental ferroelectric dispersion observed around T_{c1}. These changes are explained in terms of clusters sizes and dynamics in the framework of order-disorder type phase transition mechanism.
Measurements of the heat capacity in ultralow temperatures (down to 350 mK) have been carried out for Ce_{1-x}La_{x}NiAl_4. The paramagnetic behavior above about 30 K can be well described by the Curie-Weiss magnetic susceptibility. The undoped CeNiAl_4 compound is a known heavy fermion system with a large electronic specific heat coefficient (γ = 0.5 J mol^{-1} K^{-2}) and the Kondo temperature in the range 30-80 K. In the case of the Ce_{0.8}La_{0.2}NiAl_4 and Ce_{0.6}La_{0.4}NiAl_4 compounds a peak in C/T appears below 2 K, which is strongly damped by the magnetic field. It is probably connected with the Kondo and/or magnetic interactions and the electronic specific heat coefficient is 0.19 J mol^{-1} K^{-2} (0.43 J mol^{-1} K^{-2}) for x = 0.2 (x = 0.4) at T → 0. The value determined above the peak, at temperature for which the magnetic field starts to decrease γ ( ≈ 3 K), is about 0.5 J mol^{-1} K^{-2} and the effect of the magnetic field can be well analyzed in frames of the single-ion Kondo model.
We report on the investigation of recently discovered heavy fermion compounds within the Ce-Pd-In system. Single crystals of Ce_{n}Pd_{m}In_{3n+2m} (n=2, 3, 5; m=1, 2) and Ce_{4}Pd_{10}In_{21} were synthesized from In-flux. Specific heat measurements of the multiphase Ce_{n}Pd_{m}In_{3n+2m} system revealed a superconducting transition at T_{c}=0.69 K arising from Ce_{2}PdIn_{8} and another, magnetic transition at T_{m}=1.67 K arising from either Ce_{3}PdIn_{11} or Ce_{5}Pd_{2}In_{19}. Low-temperature data of Ce_{4}Pd_{10}In_{21} display ferromagnetic long-range order below 0.8 K.
Isobaric heat capacities and internal pressures of cyclopentanol at pressures up to 100 MPa and temperatures ranging from 293 to 318 K were determined by the acoustic method. The obtained results were compared with those of pentan-1-ol in order to study the influence of the molecular configurations comprising cyclic and normal-chain structures on pressure and temperature dependence of the thermodynamic properties. It was found that the temperature and pressure coefficients of internal pressure were sensitive to the structural organization of the liquid and reflected the character of the interactions.
Thermodynamic studies of the anion-radical salt system [Ni(bipy)₃](TCNQ)₄·(CH₃)₂CO, where TCNQ is 7,7',8,8'-tetracyano-quinodimethane, are reported. The anion-radical salt systems based on TCNQ belong to a material class in which the arrangement of the anion-radical salt has considerable impact on the charge transfer and magnetic properties. The crystal structure of the studied compound consists of [Ni(bipy)₃]⁺² cations containing Ni⁺² ions and four types of crystallographically independent anion-radicals TCNQ^{·-} (A, B, C and D). These TCNQ^{·-} radicals form two different types of TCNQ^{·-} stacks (AABB and CCDD), where a strong exchange interaction is expected. The temperature dependence of the specific heat of a single crystal was studied in magnetic fields up to 5 T and in the temperature range from 0.4 K to 30 K. The temperature dependence of specific heat displays a broad Schottky-like maximum above 0.4 K. Using a single-ion approximation, the analysis of the temperature dependence of the specific heat below 10 K yields values for the anisotropy parameters, D/k_{B}=-1.95 K and E/k_{B}=0.3 K. These results suggest that the observed maximum in the specific heat originates from Ni⁺² ions while the exchange interaction between the transition metal ions and the TCNQ is negligible.
High-quality single crystal of a novel cerium silicide CeRh_3Si_2, crystallizing with the orthorhombic ErRh_3Si_2-type structure, was grown by the Czochralski pulling method and studied by means of specific heat measurements. The antiferromagnetic ordering of the compound manifests itself as a pronounced lambda-shaped anomaly at T_N = 4.72(3) K, and is followed by a spike-shaped anomaly due to spin reorientation at T_t = 4.48(2) K, in good agreement with the previously reported magnetic susceptibility data. Both transitions are very sensitive to applied magnetic field - they split into four separate anomalies, which independently shift to lower temperatures with rising field. Several scenarios are proposed as possible explanations of the multi-step character of the magnetic ordering in CeRh_3Si_2.
New equations, which have analytical solutions, for lattice and electronic heat capacities, entropies and enthalpies at constant volume and constant pressure were derived by using kinetic theory, Kirchhoff and Stefan-Boltzmann laws and Wien radiation density equation. These equations were applied to the experimental constant volume heat capacity data of copper. The temperature Θ_{V} corresponding to 3R/2 was found to be 78.4 K for copper. Copper shows the dimensionality crossover from 3 to 2 at about 80 K. The Θ_{V}(T) is proportional to Debye temperature. The relationship between dimension and Θ_{V} was given. Temperature dependence of Debye temperature and non-monotonic behavior were discussed. The heat capacity and entropy values, predicted by the proposed models were compared with the values predicted by the Debye models. The results have shown that the proposed models fit the data better than the Debye models. Enthalpy equations derived in this study were compared with the polynomial model and a good fitting was obtained. The equation for the photon absorption equilibrium constant of copper was derived.
Specific heat of the Ce(Ni_{1 - x}Cu_{x})_4Mn compounds has been studied. The samples are prepared by induction melting and it is found, based on the X-ray diffraction, that all the compounds keep the CaCu_5-type structure. This series exhibits a transition between the ferromagnetically ordered CeNi_4Mn and the spin-glass CeCu_4Mn compounds, which is well visible in the measurements of the ac susceptibility peak as a function of the magnetic field frequency and in the magnetization relaxation. In the present research we explore the behavior of the specific heat for various x. The changes of the electronic specific heat coefficient γ are determined by analysis of the low temperature part of the C_{p}/T(T^2) dependence. We also observe that the magnetic phase transition is only detectable in the specific heat signal after extraction of the magnetic contribution of the Mn atoms. This is carried out by subtraction of the specific heat of the reference sample.
In the paper we present adiabatic calorimetry and dielectric spectroscopy results for 2,3-dimethylbutan-2-ol (2,3-DM-2-B), one of the isomers of neohexanol. For 2,3-DM-2-B we have detected the following phase transitions: C2 (249.8 K) → C1 (262 K) → Is. No glass phase was found. In both crystalline phases C2 and C1 three relaxation processes were detected. These processes are discussed in relation to the calorimetric studies.
The specific heat of YbNi_4Si has been analyzed considering the electronic contribution and the lattice contributions in frames of the Debye model. Based on the specific heat measurements, the electronic specific heat coefficient γ = 25 mJ mol^{-1} K^{-2} and the Debye temperature θ_D = 320 K were derived. This small value shows that YbNi_4Si cannot be classified as a heavy fermion system. These studies are completed by magnetic susceptibility, X-ray photoemission spectroscopy, and electrical resistivity.
The electronic structure, pressure and temperature dependence of thermodynamic properties of RNi₅Sn (R = La, Ce, Pr, Nd) compounds are calculated by ab initio full potential local orbital minimum-base(ver. 9 and ver. 14) method. These compounds crystallize in the hexagonal crystal structure (space group P6_{c}/mmc, No. 194). The band calculations were performed in the scalar-relativistic mode for the exchange correlation potentials in the form of the Perdew-Burke-Ernzerhof general gradient approximation. In this work we present the band structures of LaNi₅Sn, CeNi₅Sn, NdNi₅Sn and PrNi₅Sn compounds. The thermodynamic properties (bulk modulus, Debye temperature) are calculated in the Debye-Grüneisen model using the equation of states in the form of Birch-Murnaghan, Poirier-Tarantola and Vinet. Our results have shown that values of thermodynamic properties depend on the method of calculations.
The results of study of Pb influence on high temperature magnetic and thermal properties of the chalcogenides (Pb_ySn_{1-y})_2P_2S_6 are presented. The increasing Pb content shifts phase transition to the ferroelectric state at about 337 K towards lower temperatures while magnetic field till 3 T has no influence on this transition. The measured susceptibility and magnetisation data are discussed.
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