Thermal conductivity of the vitreous system (ZnO) x −(P2O5)1−x

Glasses of the system (ZnO)_x–(P₂O₅)_1–x have been prepared by melting ZnO with anhydrous P₂O₅ in open crucibles. These glasses had compositions ranging from 20 to 70 mol % ZnO (chemically analysed ZnO mol %). Measurements of the thermal conductivity for the present glass system have been made in the temperature range 305 to 630 K. The thermal conductivity of this glass system is mainly due to lattice thermal vibrations. The thermal conductivity data are found to be fairly sensitive to the ZnO mol % content. It is observed from these data that the present glass system can be divided into three compositional regions. This behaviour is qualitatively explained in terms of changes in glass structure.     

Optical, electrical and thermal studies on (As2Se3)3−x(As2Te3)x glasses

Optical properties and conductivity of glassy (As₂Se₃)_3−x(As₂Te₃)_x were studied for 0 ≤ x ≤ 3. The films of the above mentioned compound were prepared by thermal evaporation with thickness of about 250 nm. The optical-absorption edge is described and calculated using the non-direct transition model and the optical band gap is found to be in the range of 0.92 to 1.84 eV. While, the width of the band gap tail exhibits opposite behaviour and is found to be in the range of 0.157 to 0.061 eV, this behaviour is believed to be associated with cohesive energy and average coordination number. The conductivity measurement on the thin films is reported in the temperature range from 280 to 190 K. The conduction that occurs in this low-temperature range is due to variable range hopping in the band tails of localized states, which is in reasonable agreement with Mott's condition of variable range hopping conduction. Some parameters such as coordination number, molar volume and theoretical glass transition temperature were calculated and discussed in the light of the topological bonding structure.     

Electrical conduction in some (CnH2n) (NH 3 + )2 FeCl4 compounds

The d.c. conductivity, a.c. conductivity and thermoelectric power of the compounds H₃N₊(CH₂)₊ NH₃FeCl₄, wheren=2, 3, 7 and 10, have been studied over a temperature range of 150–500 K. The conductivity results confirm the presence of more than one structural phase transition for each compound investigated. The thermoelectric power measurements showed that electrons are the main charge carriers in all crystal phases. The conductivity results were explained on the basis of an electron hopping mechanism over the whole temperature range.     

Dielectric properties of K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3

Dielectric constant (ɛ), dielectric loss (tan δ) and conductivity (σ) for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ have been measured over the frequency range 100 Hz — 100 kHz and in temperature range 30°C — 400°C. The values of static dielectric constant at room temperature are 7.67 and 4.80 for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively. The plots of log σ against reciprocal temperature at different frequencies of these samples merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0.67 eV and 1.98 eV for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively.     

Low temperature conductivity of Gd2(SO4)38H2O and Dy2Ti2O7 as a function of magnetic field

The thermal conductivities of pressed powders of Gd₂(SO₄)₃8H₂O and Dy₂Ti₂O₇ and a single crystal of Gd₂(SO₄)₃8H₂O were measured in the range 3 to 9 K. At approximately 4 K the thermal conductivities were measured as a function of magnetic field from 0 to 1.8 T. The single crystal had better thermal conductivity than the pressed powders and no significant field dependence was detected in any sample.     

Electrical conductivity of polycrystalline Fe2(MoO4)3

Measurements of the electrical conductivity of polycrystalline Fe₂ (MoO₄)₃ in the temperature range 370 to 900 K and in the oxygen partial pressure region 10^?4 to 1 atm are presented. Fe₂(MoO₄)₃ is found to be a semiconductor. Differing conduction mechanisms operate, depending on the crystallographic form of Fe₂(MoO₄)₃ and the oxygen partial pressure, and their nature is discussed.     

Phase equilibria in the liquid ternary system [Y(NO3)3(TBP)3]-[UO2(NO3)2(TBP)2]-C14H30 at different temperatures

The phase diagrams of the ternary system [Y(NO₃)₃(TBP)₃]-[UO₂(NO₃)₂(TBP)₂]-tetradecane in the temperature range 298.15–333.15 K were constructed. These diagrams contain the field of homogeneous solutions and the field of separation into two liquid phases (I, II). Phase I is enriched in [Y(NO₃)₃(TBP)₃] and [UO₂(NO₃)₂(TBP)₂], and phase II is enriched in tetradecane. With increasing temperature, the two-phase fields contract. The critical points of the ternary liquid systems depend on temperature. In the two-phase systems, [UO₂(NO₃)₂(TBP)₂] is preferentially distributed in phase I, although the binary system [UO₂(NO₃)₂(TBP)₂] tetradecane is homogeneous over the entire temperature range. Original Russian Text ? V.A. Keskinov, V.V. Lishchuk, A.K. Pyartman, 2007, published in Radiokhimiya, 2007, Vol. 49, No. 5, pp. 417–419.     

Thermal Conductivity Measurements of Aqueous SrCl2 and Sr(NO3)2 Solutions in the Temperature Range Between 293 and 473 K at Pressures up to 100 MPa

Accurate high-pressure thermal conductivity measurements have been performed on H₂O+SrCl₂ and H₂O+Sr(NO₃)₂ mixtures at pressures up to 100 MPa over a temperature range between 293 and 473 K using a parallel-plate apparatus. The concentrations studied were 0.025, 0.05, 0.10, 0.15, and 0.20 mass fraction of the salts. The estimated accuracy of the method is about ±1.6%. The pressure, temperature, and concentration dependences of the thermal conductivity have been studied. Measurements were made on six isobars, namely, 0.1, 20, 40, 60, 80, and 100 MPa. The thermal conductivity shows a linear dependence on pressure and concentration for all isotherms. Along each isobar, a given concentration shows the thermal-conductivity maximum at a temperature of about 413 K. The measured values of thermal conductivity at atmospheric pressure are compared with the results of other investigators. Literature data at atmospheric pressure reported by Ridel and by Zaitzev and Aseev agree with our thermal conductivity values within the estimated uncertainty.     

Phase Separation in the Ternary Liquid System [Nd(NO3)3(TBP)3]-[UO2(NO3)2(TBP)2]-Tetradecane at Different Temperatures

Phase diagram of the ternary liquid system [Nd(NO₃)₃(TBP)₃]-[UO₂(NO₃)₂(TBP)₂]-tetradecane at 288.15–345.15 K is studied. There are homogeneous and two-phase regions in the diagram. One of the phases (I) is enriched with [Nd(NO₃)₃(TBP)₃] and [UO₂(NO₃)₂(TBP)₂], and the second phase (II), with tetradecane. The two-phase region decreases with increasing temperature. The upper critical temperature of solution (mixing) of the binary and ternary systems is T _cr = 344.85±0.5 K. The critical compositions of the ternary liquid system depend on the temperature. The two-phase systems demonstrate preferential concentration of [UO₂(NO₃)₂(TBP)₂] in phase I, despite the fact that the binary system [UO₂(NO₃)₂(TBP)₂]-tetradecane is homogeneous over the entire temperature range studied. __________ Translated from Radiokhimiya, Vol. 47, No. 2, 2005, pp. 154–157. Original Russian Text Copyright ? 2005 by Pyartman, Keskinov, Mishina, Kudrova.     

Structural phase transitions and negative thermal expansion in Sc2(MoO4)3

The thermal expansion and phase transitions of the framework material Sc₂(MoO₄)₃ have been investigated from 4 to 300 K by powder neutron diffraction, and from 300 to 1053 K by dilatometry. Below 178 K Sc₂(MoO₄)₃ has a monoclinic structure, which has been determined using Rietveld refinement of X-ray and neutron powder diffraction data collected at 50 K; space group P2₁/a with a=16.22715(9), b=9.58051(6), c=18.9208(1) Å, β=125.3988(4)°. Monoclinic Sc₂(MoO₄)₃ has a positive coefficient of thermal expansion, α_V=+2.19×10⁻⁵ K⁻¹ between 4 and 170 K. There is significant anisotropy in thermal expansion with the monoclinic b-axis having a negative expansion coefficient between 4 and 86 K. Above 180 K Sc₂(MoO₄)₃ has the orthorhombic Sc₂(WO₄)₃ structure and has a negative coefficient of thermal expansion with α_V=−6.3×10⁻⁶ K⁻¹ between 180 and 300 K. The structure has been determined between 4 and 300 K using a parametric approach to Rietveld refinement. Structural changes at the monoclinic to orthorhombic phase transition are shown to be intimately related to the contraction of the orthorhombic temperature phase. Dilatometry measurements show that negative thermal expansion continues up to 1053 K.     

Dielectric properties of Bi4(GeO4)3 and Bi4(SiO4)3

Dielectric constant, dielectric loss and conductivity of Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ single crystals have been measured as a function of frequency and in the temperature range from liquid nitrogen temperature to 400° C. The values of the static dielectric constant at room temperature are 16·4 and 13·7 for Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ respectively. The plots of log (σ) against reciprocal temperature at different frequencies of these crystals merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0·95 eV and 1·2 eV for Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ respectively.     

Preparation of ZrF4-NaF-BaF2-LaF3-YbF2 glasses with YbF2 substitution for BaF2 (LaF3)

We have prepared glasses and semicrystalline phases with a green color in the systems ZrF₄(53.5)-NaF(20)-BaF₂(20)-LaF₃(6.5 ? x)-YbF₂(x) (0 ≤ x ≤ 6.5 mol %) (I) and ZrF₄(53.5)-NaF(20)-BaF₂(20 ? x)-LaF₃(6.5)-YbF₂(x) (0 ≤ x ≤ 20 mol %) (II). Thermal analysis results demonstrate that, in both systems, the glass transition temperature of the samples containing ≤3 mol % YbF₂ lies in the range 200–250°C, their heating curves show two or three crystallization events (at 320–340, 380–460, and 415–490°C), and their melting points range from 460 to 490°C. Increasing the YbF₂ content of the glasses to 4 mol % and above (system I) has no effect on their glass transition temperature, reduces the temperature of the first crystallization event from 340 to 305°C, and produces extra peaks in the range 545–600°C, above the major melting peak, which can be accounted for by a nonequilibrium state of the glasses. Ytterbium difluoride substitution for barium difluoride (10 to 20 mol %) (system II) leads to the formation of semicrystalline phases and increases the glass-transition (305°C), crystallization (470–515°C), and melting (570–690°C) temperatures. The IR spectra of such samples show, in addition to a so-called “featureless continuum” (～500 cm^?1), absorption bands characteristic of the Yb-F bond. Electronic spectra also confirm that the glasses contain both divalent and trivalent ytterbium.     

Study of thermal properties of glass system 77% B2O3-23% PbO doped with ZnO in the temperature range 300 to 700 K

The thermal properties: specific heat capacity (C _p), thermal conductivity (), and thermal diffusivity (a) of the glass system 77% B₂O₃-23% PbO doped with ZnO, were measured in the temperature range 300 to 700 K. It was found that electronic conduction has no significant contribution to the thermal conductivity. The main mechanism of heat transfer is therefore due to both phonons and photons. A discussion of the results is made in view of various theoretical aspects.     

Low temperature phonon thermal conductivity of the quasi-one-dimensional compounds (NbSe4)3I, (TaSe4)2I and K0.3MoO3

We report on measurements of the thermal conductivity of quasi-one-dimensional compounds K_0.3MoO₃, (NbSe₄)₃I, and (TaSe₄)₂I between 0.07K and 4 K. Despite the presence of a charge-density wave, the observed behaviour is similar to that expected in good insulating crystals, where the thermal conductivity well below 1 K is mainly governed by boundary scattering with some degree of specular reflection. However a pronounced anomaly is detected in (TaSe₄)₂I as a sharp maximum around 1 K, followed by a broad minimum around 3 K. We ascribe this anomaly to strong scattering by low-lying transverse acoustic phonons, with a very weak dispersion over a large part of the Brillouin zone, lying at an unusually low frequency.     

Thermal conductivity and electrical resistivity of cadmium arsenide (Cd3As2) in the temperature range 4.2–40 K

Results on electrical resistivity and thermal conductivity measured in the temperature range 4.2–40 K are presented for single-crystal and polycrystalline samples of Cd₃As₂. Hall effect has been studied at temperatures of 4.2, 77, and 300 K. The calculated value of the conduction electron concentration was in the range 1.87–1.95 10²⁴m^–3. Electrical resistivity of all investigated samples was independent of temperature up to about 10K and increased slowsly at higher temperatures. The thermal conductivity shows a maximum in the region in which the lattice component of thermal conductivity dominates. The strong anisotropy of the lattice component determines the anisotropy of the total thermal conductivity. The electronic component of thermal conductivity does not exhibit any anisotropy and shows a maximum at a temperature of about 300 K.Paper submitted to the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Phase equilibria in the liquid ternary system [Th(NO3)4(TBP)2]-[UO2(NO3)2(TBP)2]-Isooctane at different temperatures

The phase diagrams of the ternary systems [Th(NO₃)₄(TBP)₂]-[UO₂(NO₃)₂(TBP)₂]-isooctane in the temperature range 298.15–333.15 K were constructed. These diagrams contain the field of homogeneous solutions and the field of separation into two liquid phases (I, II). Phase I is enriched in [Th(NO₃)₄(TBP)₂] and [UO₂(NO₃)₂(TBP)₂], and phase II is enriched in isooctane. With increasing temperature from 298.25 to 333.15 K, the mutual solubility of Th(NO₃)₄(TBP)₂ and isooctane does not change noticeably, but the two-phase fields somewhat contract. In the two-phase systems [UO₂(NO₃)₂(TBP)₂] is preferentially distributed in phase I, although the binary system [UO₂(NO₃)₂(TBP)₂]-isooctane is single-phase over the entire temperature range examined. The preferential accumulation of [UO₂(NO₃)₂(TBP)₂] in phase I causes the redistribution of [Th(NO₃)₄(TBP)₂] and isooctane into phases II and I, respectively. The compositions of the ternary systems in the critical points at different temperatures were determined. The electronic absorption spectra of uranyl nitrate solvate with TBP in the homogeneous and two-phase systems were recorded and analyzed. Original Russian Text ? A.K. Pyartman, V.A. Keskinov, V.V. Lishchuk, Ya.A. Reshetko, 2007, published in Radiokhimiya, 2007, Vol. 49, No. 5, pp. 420–422.     

快淬和球磨时间对p型(Bi_(0.25)Sb_(0.75))_2Te_3合金热电性能的影响

通过快淬-机械球磨-放电等离子烧结工艺制备了p型(Bi0.25Sb0.75)2Te3块体热电材料.在300~523K温度范围内对其电导率、Seebeck系数和热导率进行了测试,并系统研究了快淬后球磨时间对合金热电性能的影响.研究结果表明,随着球磨时间的延长,样品的电导率呈先降后升的趋势,Seebeck系数变化并不明显,而热导率随球磨时间的延长逐渐下降.球磨20h的样品在室温下具有最高的热电优值,最大值达到0.96,机械抗弯强度达到91MPa.     

The Thermophysical Properties of Solid Solutions of CaLa2S4-La2S3 System

The thermal conductivity coefficient in the temperature range from 275 to 450 K and the coefficient of thermal expansion in the range from 300 to 900 K are experimentally determined for solid solutions of the CaLa₂S₄-La₂S₃ system. The mechanisms of heat transfer in CaLa₂S₄- La₂S₃ samples in the investigated temperature range are discussed, as well as the factors which define the complex concentration dependence of thermal conductivity coefficient. The correlation is treated between the value and temperature dependence of the coefficient of thermal expansion and the variation of the interatomic bond force in the case of variation of the concentration of cation vacancies in the investigated crystals.     

Liquid Thermal Conductivity of Binary Mixtures of Pentafluoroethane (R125) and 1,1,1,2-Tetrafluoroethane (R134a)

Thermal conductivities of zeotropic mixtures of R125 (CF₃CHF₂) and R134a (CF₃CH₂F) in the liquid phase are reported. Thermal conductivities have been measured by a transient hot-wire method with one bare platinum wire. Measurements have been carried out in the temperature range of 233 to 323 K and in the pressure range of 2 to 20 MPa. The dependence of thermal conductivity on temperature, pressure, and composition of the binary mixture is presented. Measured thermal conductivity data are correlated as a function of temperature, pressure, and overall composition of the mixture. The uncertainty of our measurements was estimated to be better than 2%.     

Thermodynamic properties of NaZr2(PO4)3

The heat capacity of crystalline NaZr₂(PO₄)₃ was measured between 7 and 340 K by adiabatic calorimetry. The results were used to calculate the thermodynamic functionsC _p ⁰ ,H ⁰(T) -H ⁰(0),S ⁰(T), andG ⁰(T) -H ⁰(0) in the range 0-340 K. The absolute entropy was found to be S⁰NaZr₂(PO₄)₃, cr, 298.15 K) = 327.1 ±1.0 J/(mol K), and the standard entropy of formation Δ_fS⁰(NaZr₂(PO₄)₃, cr, 298.15 K) = -1101±1 J/(mol K). Solution calorimetry was used to determine the standard enthalpy of formation, Δ_f H ⁰(NaZr₂(PO₄)₃, cr, 298.15 K) = -5236 ±5 kJ/mol. By combining the data obtained by the two techniques, the standard Gibbs energy of formation was determined to be Δ_fG⁰(NaZr₂(PO₄)₃, cr, 298.15 K) = -4908 ±5 kJ/mol.