Low temperature specific heat of single-domain and polydomain ferroelectric NaNO2

The specific heat of a NaNO₂ sample has been measured between 2 K and 40 K in both single-domain and polydomain states. In this region the specific heat of the single domain sample follows exactly the T³ dependence. A clear excess contribution which in this temperature range has a temperature dependence between T and T² has been detected for the polydomain sample. It is attributed to domain walls.     

Molekül- und Gitterschwingungen im Natriumhyperoxid

We have measured the Raman spectrum of clear NaO₂ single crystals of mm size. In addition to the usual lattice modes we observe a purely molecular mode. The Raman line of 1156 cm^?1 at 300 K corresponds to the value which was proposed in the literature for the vibrational frequency of the O₂ ^? ion. This confirms the fact that the alkali hyperoxides are ionic crystals. The investigation of the Raman spectrum between 6 K and 300 K permits an accurate determination of the temperature dependence of the O₂ ^? stretching frequency. The results display structural phase transitions at 230 K and 201 K in agreement with the previous findings of specific heat measurements and X-ray analysis.     

The specific heat of C-phase Gd2O3

The specific heat of C-phase (almost cubic) Gd₂O₃ has been measured between 1.4 and 18 K. It shows a broad peak at 2.0 K. While the peak can be fit by a Schottky specific heat curve, the weight of all the experimental evidence to date indicates that the specific heat is due to magnetic ordering of the Gd⁺⁺⁺ ions. The implications of the results on the technological applications of C-phase Gd₂O₃ are discussed.     

Experimental and theoretical studies on high-temperature thermal properties of fibrous insulation

In the present paper, an experimental apparatus has been developed to measure heat transfer through high-alumina fibrous insulation for thermal protection system. Effective thermal conductivities of the fibrous insulation were measured over a wide range of temperature (300-973 K) and pressure (10⁻²-10⁵ Pa) using the developed apparatus. The specific heat and the transmittance spectra in the wavelength range of 2.5-25 μm were also measured. The spectral extinction coefficients and Rosseland mean extinction coefficients were obtained from transmittance data at various temperatures to investigate the radiative heat transfer in fibrous insulation. A one-dimensional finite volume numerical model combined radiation and conduction heat transfer was developed to predict the behavior of the effective thermal conductivity of the fibrous insulation at various temperatures and pressures. The two-flux approximation was used to model the radiation heat transfer through the insulation. The experimentally measured specific heat and Rosseland mean extinction coefficients were used in the numerical heat transfer model to calculate the effective thermal conductivity. The average deviation between the numerical results for different values of albedo of scattering and the experimental results was investigated. The numerical results for ω=1 and experimental data were compared. It was found that the calculated values corresponded with the experimental values within an average of 13.5 percent. Numerical results were consistent with experimental results through the environmental conditions under examination.     

Low-temperature specific heats of lanthanum and yttrium phosphate glasses

Summary The specific heats of (R₂O₃) _x (P₂O₅)_1−x glasses containing high concentrations of La³⁺ and Y³⁺ ions have been measured between 1.5K and 30K. It is shown that, in addition to the usual Debye contribution, there is an excess specific heat arising from localized vibrational states which has been discussed in terms of two distinct models. The first predicts a maximum in the temperature dependence of the excess specific heat associated with the crossover frequency from phonon to fracton behaviour. The phonon-fracton density of states used to fit the excess specific heat gives rise to model parameters having the same magnitudes as those found previously for other glasses including samarium phosphates. The second model, formulated on the basis of soft vibrations in glasses, predicts a minimum in the excess specific heat, which is also observed. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Capanello, Italy, July 4–8, 1994.     

Some properties of the phonon spectra of transition metal disilicides VSi2, NbSi2, and TaSi2

The phonon spectra of metallic disilicides VSi₂, NbSi₂, and TaSi₂ have been studied in detail by inelastic neutron scattering at 300 K and specific heat measurements between 10 K and 250 K. The specific heat calculated from the generalised phonon density of states extracted from neutron measurements is in good agreement with the measured lattice contribution to the specific heat. The properties of the phonon spectra are discussed in relation with other data reported for these isostructural and isoelectronic disilicides.     

Effect of heavy cation doping on thermal properties of LaMnO3

Effect of heavy cation doping (Ca²⁺ at the A-site) on the thermal properties of perovskite LaMnO₃ has been investigated using the Rigid Ion Model (RIM)). As strong electron-phonon interactions are present in these compounds, the lattice part of the specific heat deserves proper attention. The specific heat of magnetoresistance compound La_0.25Ca_0.75MnO₃ as a function of temperature (10 K ≤ T ≤ 300 K) is reported. Our results on specific heat are in good agreement with the measured values of specific heat at lower temperatures. In addition, the results on the cohesive energy (ϕ), molecular force constant (f), Restrahalen frequency (ν ₀), Debye temperature (Θ _D) and Gruneisen parameter (γ) are also discussed.      

Crystal field effects in TmCu2 compound

The splitting of the³H₆ multiplet has been estimated for the Tm³⁺ ion in the crystal electric field of the orthorhombic TmCu₂ compound. Using the energy levels and appropriate eigenfunctions the crystal field only susceptibility has been calculated along the principal orthorhombic axes at temperatures 10 to 300 K. The obtained results are compared with our measurements of specific heat and paramagnetic susceptibility on polycrystalline sample.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.     

Specific heat of single phase Nb3Ge

For the first time, the specific heat of single phase, stoichiometric, high transition temperature (21.8 K) A-15 Nb₃Ge has been measured. From the data between 4 and 29 K, the linear term coefficient, γ, of the specific heat is found to be 30.3±1. mJ/mole-K² and the Debye temperature, ?_D, is 302±2 K. The bulk energy gap parameter, 2Δ/kT_c, is found to be 4.2±0.2, in agreement with tunneling measurements.     

Non-linear temperature dependence of the low temperature specific heat of vitreous B2O3

The specific heat of virteous B₂O₃ has been measured between 50 mK and 1 K. The excess to the calculated acoustic term is found to vary as T^1.45 below 0.7K as opposed to the linear law generally observed. This may be attributed to the particular structure of this glass.     

Antiferromagnetic linear chains in the crystalline free radical tanol

TANOL (tetramethyl-2,2,6,6, piperidinol-4, oxyl-1), which shows a broad maximum in its specific heat near 4 K was known as an example of the Heisenberg type one-dimensional antiferromagnet. The specific heat has been measured down to 0.35 K. A sharp peak appears at 0.49 K (T_N) and a T³ law is observed in the low temperature region. The interchain interactions which can be deduced are the same order of magnitude as the spin-spin dipolar interactions. The linear chain characteristics of TANOL are compared to those of some other products.     

Thermodynamic properties of OsB under high temperature and high pressure

The energy-volume curves of OsB have been obtained using the first-principles plane-wave ultrasoft-pseudopotential density functional theory (DFT) within the generalized gradient approximation (GGA) and local density approximation (LDA). Using the quasi-harmonic Debye model we first analyze the specific heat, the coefficients of thermal expansion as well as the thermodynamic Grüneisen parameter of OsB in a wide temperature range at high pressure. At temperature 300 K, the coefficients of thermal expansion α_V by LDA and GGA calculations are 1.67×10⁻⁵ 1/K and 2.01×10⁻⁵ 1/K, respectively. The specific heat of OsB at constant pressure (volume) is also calculated. Meanwhile, we find that the Debye temperature of OsB increases monotonically with increasing pressure. The present study leads to a better understanding of how the OsB materials respond to pressure and temperature.     

Specific heat and critical behavior of Tl0.3MoO3 near the Peierls phase transition

The specific heat of the quasi-one-dimensional charge-density-wave (CDW) compound Tl_0.3MoO₃ has been measured using an adiabatic continuous heating method from 100 to 220 K. A specific heat jump associated with the Peierls phase transition occurs at 172.3 K. A good scaling relation between the excess specific heat and the susceptibility is found between 140 K and 190 K. Further analysis indicates that the width of the critical region of Tl_0.3MoO₃ is about 10 K and the specific-heat critical behavior can be well described by the three-dimensional XY model.     

The specific heat of bulk amorphous arsenic

The specific heat of bulk amorphous arsenic deposited from the vapor at 415°K has been measured between 1.8 and 20°K. A comparison with compacted amorphous As films deposited at room temperature reveals appreciable differences in the form of C/T³. The results indicate a relative increase in the density of low frequency vibrational modes in the bulk amorphous As. The specific heat measurements support x-ray and Raman scattering studies that suggest variations in the local structure of amorphous As prepared under different deposition conditions. A comparison with neutron scattering measurements in bulk amorphous As also indicates an underestimate of the low frequency density of states.     

Thermally Stimulated Depolarization Current and Thermal Analysis Studies of Gamma Irradiated Lithium‐Salt/Polymer Electrolyte Blends

Thermally stimulated depolarization current (TSDC) and thermal analysis studies of gamma irradiated LiOH/PVA blends were done. To study the mechanisms of conduction and TSDC in poly(vinyl alcohol) (PVA) and LiOH/PVA blends, short circuit TSDC at a polarizing temperature 353 K with a polarizing field of 3 kV cm^?1 have been analyzed in the temperature range 300–410 K. Two peaks are evident from the global TSDC measurements on the pure PVA homopolymer. Meanwhile, in all blended samples; there is only one broad peak with a shoulder on the high temperature side due to the relaxation of the poly‐blend system. The temperature dependence, 300–408 K, of the current density (J) for pure PVA and its blended samples has been studied. It was observed that J values increase dramatically with increasing temperature (in the low temperature region from 300–340 K) owing to the formation of local ordered regions in the otherwise disordered amorphous matrix of PVA. Further increase in the temperature caused a marginal increase in J values. The temperature dependence of the specific heat for all samples was measured. A linear increase of C _p was observed with an increase in temperature, which is ascribed to the increase in lattice vibration of linear macromolecules and consequently, increases in the number of internal degree of freedom of phonons.     

重电子金属CeCu5.8M0.2（M=Ni,Zn, Cd）低温物性的比较

研究了不同元素等量掺杂下重电子金属CeCu_5.8M_0.2(M=Ni，Zn，Cd)低温电阻、比热容和磁化率随温度的变化关系.分析讨论了掺杂元素M(M=Ni，Zn，Cd)的磁性、价态及原子尺寸对近藤温度T_K、相干温度（即电阻极大值的温度Ｔ^R_max）、每个Ce离子在较高温度时的平均磁矩μ_Ｂ以及在温度降低时被传导电子自旋屏蔽过程的影响. 关键词： 重电子系统 低温电阻 低温比热容 磁化率     

Specific heat of Tb x Y1−x Sb mixed crystals

The specific heat of Tb _x Y_1?x Sb mixed crystals (x=0, 0.103, 0.383, 0.428, 0.467, 0.635, 0.928 and 1.0) has been measured between 1.6 and 20°K using an adiabatic calorimeter. The crystal field potential is described well taking into account only 4th order terms, and the overall splitting of the ground multiplet⁷F₆ of the Tb³⁺ ion has been found to be 115°K independent of the concentrationx. Forx>0.46 the specific heat curves exhibit a behaviour typical for a second order phase transition. For lower concentrations a normal Schottky anomaly is found and no evidence for magnetic order was detected. The experimental results which are in agreement with magnetic measurements are compared with molecular field calculations including crystal field and exchange interaction.     

Thermodynamic properties of the CeSn3 mixed valence compound

We have measured on the CeSn₃ compound, the expansion coefficient between 80 and 800 K at normal pressure, the isothermal compressibility in the 0–8 GPa pressure range at room temperature and the heat capacity at constant pressure in the 60–300 K temperature range. The experimental data were compared with those previously found for the isomorphous LaSn₃ phase, assumed as a proper reference material for the study of the intermediate valency states in CeSn₃. Both the thermal expansion (3α) and the isothermal compressibility (k) of CeSn₃ show behaviours quite different from those of LaSn₃: for instance, in the standard conditions, 3α is 55 × 10^?6K^?1for CeSn₃ and 38 × 10^?6K^?1for LaSn₃; k is 15 × 10^?12 Pa^?1 and 12 × 10^?12 Pa^?1 respectively for CeSn₃ and LaSn₃. The thermal behaviour of the molar specific heat at constant pressure of CeSn₃ is similar to that of LaSn₃ for temperatures lower than 50 K. In the 70–300 K temperature range, the heat capacity of CeSn₃ is clearly higher than that of LaSn₃, ΔC_p being maximum near 150 K. The analysis of the calorimetric data show that the electronic coefficient γ of CeSn₃ is temperature dependent: its value varies from 53 mJ K^?2 mole^?1 at low temperature 24 mJ K^?2 mole^?1 at 300 K.     

Thermodynamic and kinetic properties of an icosahedral quasicrystalline phase in the Al-Pd-Tc system

The properties of a quasicrystalline phase in the Al-Pd-Tc system are studied for the first time. X-ray investigations demonstrate that the quasicrystalline phase in the Al₇₀Pd₂₁Tc₉ alloy has a face-centered icosahedral quasi-lattice with parameter a=6.514 ?. Annealing experiments have revealed that this icosahedral phase is thermodynamically stable. The heat capacity of an Al₇₀Pd₂₁Tc₉ sample is measured in the temperature range 3–30 K. The electrical resistivity and magnetic susceptibility are determined in the temperature range 2–300 K. The electrical resistivity is found to be high (600 μΩ cm at room temperature), which is typical of quasicrystals. The temperature coefficient of electrical resistivity is small and positive at temperatures above 50 K and negative at temperatures below 50 K. The magnetic susceptibility has a weakly paramagnetic character. The coefficient of linear contribution to heat capacity (γ=0.24 mJ/(g-atom K²)) and the Debye characteristic temperature (Θ=410 K) are determined. The origin of the specific features in the vibrational spectrum of the quasicrystals is discussed. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 12, 2000, pp. 2113–2119. Original Russian Text Copyright ? 2000 by Mikheeva, Panova, Teplov, Khlopkin, Chernoplekov, Shikov.     

An accurate determination of the excess low temperature heat capacity of a superconducting metallic glass

The specific heat of an amorphous superconductor Zr₃Rh (T_{c = 4.3 K}) has been measured in the temperature range from 0.35 K to 10 K and with an applied magnetic field of 75 kG. The high field suppresses superconductivity and allows accurate determination of the phonon (βT³) term for the lowest temperatures studied. A careful subtraction of the normal electronic specific heat (γT) and phonon terms reveals a well defined excess linear heat capacity γ'T at low temperature. This excess term is attributed to localized lattice excitations using the two-level tunneling defect model of Phillips.