Effect of the cooling rate on the thermoelectric properties of p-type (Bi0.25Sb0.75)2Te3 and n-type Bi2(Te0.94Se0.06)3 after melting in the bismuth-telluride system

The p-type (Bi_0.25Sb_0.75)₂Te₃ and n-type Bi₂(Te_0.94Se_0.06)₃ ingots were prepared by cooling at various cooling rates C after melting so that they have an intermediate state between the polycrystalline and Bridgman ingots which lowers their thermal conductivity κ, where C was changed from 0.10 to 2375 K/min in an evacuated glass tube. When the ingots were cooled at C = 0.50 K/min under the uniaxial temperature gradient of 5 K/cm, it was observed that the c axis of some grains points to the freezing direction. The electrical resistivity ρ, Seebeck coefficient α and κ of ingots were measured at 298 K along the freezing direction, so that ρ and κ at C = 0.50 K/min were lower by 20-30% and 9% than those of the corresponding Bridgman ingots. The thermoelectric figure of merits ZT(=α²T/ρκ) estimated for the p- and n-type ingots then reached high values of 1.27 and 1.25 at 298 K, respectively.     

Thermal Relaxation in 3He Solid Films on Graphite

The thermal conductance (κ) between ³He solid films and graphite substrates is measured in weak magnetic fields of 0, 150, 300, and 600 Oe by a relaxation method. κ is markedly reduced in a magnetic field of 150 Oe and shows complicated magnetic-field-dependent variations. Previous measurements have revealed that heat flows along ³He solid films over a long distance and then flows into the graphite substrate at some local spots. The reduction in κ in magnetic field indicates an increase in the length of the thermal flow path and a decrease in the number of local spots through which heat is transferred to the graphite substrate. These suggest the important role of magnetic impurities present in the graphite substrate. The temperature-dependent variation in the ratio of κ and heat capacity (C), κ/C, is nearly unchanged when the magnetic field increases from 150 to 600 Oe, while κ shows complicated variations. κ/C shows a clear minimum at a temperature around 1 mK, which depends on the areal density of ³He. Above and below this temperature, heat transfer is thought to take place along the solid ³He film, respectively by phonons and spin excitations.     

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m^?1 K^?1 associated to a coefficient of thermal expansion of 12 × 10^?6 °C^?1 and a density of 6.6 g cm^?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λ_Cu = 400 W m^?1 K^?1, α_Cu = 17 × 10^?6 °C^?1, ρ_Cu = 8.95 g cm^?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.     

Crystal data and thermal expansion of tricalciumborate

Single crystals of tricalciumborate were grown by the flux method. Ca₃B₂O₆ crystallizes in the rhombohedral system with the unit cell parameters $\text{a}{}_{\mathrm{R}}\text{= 6.3577(7)}\text{A}\text{?}$, α_R = 85.68(8)°, Z = 2. The equivalent hexagonal lattice parameters are a_H = 8.640(1), $\text{C}{}_{\mathrm{H}}\text{= 11.854(1)}\text{A}\text{?}$. The anisotropic thermal expansion parameters α_a = (1.00 ± 0.14) × 10^?5, α_c = (3.60 ± 0.47) × 10^?5 were determined by X-ray methods in the temperature interval 25 – 1000°C.     

Evidence for a Self-bound Liquid State and the Commensurate–Incommensurate Coexistence in 2D 3He on Graphite

We made heat-capacity measurements of two dimensional (2D) ³He adsorbed on graphite preplated with monolayer ⁴He in a wide temperature range (0.1≤T≤80 mK) at densities higher than that for the 4/7 phase (=6.8 nm^?2). In the density range of 6.8≤ρ≤8.1 nm^?2, the 4/7 phase is stable against additional ³He atoms up to 20% and they are promoted into the third layer. We found evidence that such promoted atoms form a self-bound 2D Fermi liquid with an approximate density of 1 nm^?2 from the measured density dependence of the γ-coefficient of heat capacity. We also show evidence for the first-order transition between the commensurate 4/7 phase and the ferromagnetic incommensurate phase in the second layer in the density range of 8.1≤ρ≤9.5 nm^?2.     

Competition Between the Superfluid Overlayer and the Mobile Solid Layer of 3He-4He Mixture Films on Porous Gold

In the previous quartz crystal microbalance measurements for ⁴He films adsorbed on porous gold, we have observed a competition between superfluidity and slippage: In low areal densities, the resonance frequency increases gradually below T _S due to the slippage of solid layer, while at high areal densities the slippage disappears and the superfluid onset of liquid overlayer is observed at T _C . In the crossover region, the slippage below T _S is suddenly suppressed at T _D , which is much lower than T _C . In the present work, we introduced a small amount of ³He onto ⁴He films, and studied the competition as a function of ³He areal density ρ ₃. As ρ ₃ is increased, T _C is monotonically lowered. In contrast, T _D increases up to a certain value of ρ ₃, and then turns over to decrease in parallel to T _C .     

Synthesis and crystal structure of [3,5-(CH3O)2C6H3NH3]4P4O12·4H2O

The chemical preparation and crystal structure are given for a new organic-cation cyclotetraphosphate. This compound is triclinic P-1 with the following unit cell parameters: a=7.857(1) Å, b=8.877(2) Å, c=17.271(3) Å, α=93.94(1)°, β=101.75(2)°, γ=103.72(1)° V=1137.0(4) Å³, Z=1 and ρ_cal=1.467 g cm⁻³. The crystal structure has been determined and refined to R=0.037, using 6291 independent reflections. The atomic arrangement can be described by inorganic layers parallel to the (0 0 1) planes, between which the organic entities are located.     

Decay of Turbulence Generated by Spin-Down to Rest in Superfluid 4He

We report on the extension of the experiments (P.M. Walmsley et al., Phys. Rev. Lett. 99:265302, 2007) on the decay of quasiclassical turbulence generated by an impulsive spin-down from angular velocity Ω to rest of superfluid ⁴He in a cubic container at temperatures 0.15 K–1.6 K. The density of quantized vortex lines L is measured by scattering negative ions. Following the spin-down, the maximal density of vortices is observed after time t～10Ω^?1. By observing the propagation of ions along the axis of the initial rotation, the transient dynamics of the turbulence spreading from the perimeter of the container into its central region is investigated. Nearly homogeneous turbulence develops after time t～100Ω^?1 and decays as L ∝ t ^?3/2. The effective kinematic viscosity in T=0 limit is ν=0.003κ, where κ=10^?3 cm²?s^?1 is the circulation quantum.     

Density of Vapor and Liquid Pentafluorobenzene Along the Saturation Line

The density of vapor and liquid pentafluorobenzene along the liquid–vapor coexistence curve has been studied by a gamma-ray attenuation technique over the temperature range from 293.5K to 530.9K. According to measurements, the coordinates of the critical point are T _C = (531.04 ± 0.05) K and ρ _C = (518.8 ± 2) kg · m^?3. The critical exponent β of the coexistence curve equals 0.345 ± 0.005. The results of our measurements were compared with data available in the literature. The height dependence of the density of a two-phase sample was investigated in relation to the temperature and time. These experiments made it possible to determine the isothermal compressibility of liquid and vapor phases near the critical point.     

Microwave surface resistance of epitaxial YBa2Cu3O7 thin films at 18.7 GHz measured by a dielectric resonator technique

We used a dielectric resonator technique for highly sensitive measurements of the temperature dependence of the microwave surface resistanceR _s of 1×1 cm² superconducting films at 18.7 GHz. It consists of a sapphire disc positioned on the film under investigation within a copper cavity which is acting as a radiation shield. In the TE_01δ oscillation mode the highly reproducible quality factor of about 10⁵ results in a sensitivity of ±50μΩ forR _s measurements. The temperature dependence ofR _s can be measured up to values as high as 1 Ω. We have investigated several YBa₂Cu₃O₇ thin films prepared by high oxygen pressure d.c. sputtering on LaAlO₃ and NdGaO₃. Our best films exhibit a pronounced nonlinear behavior of the d.c. resistivityρ(T) withρ(300K)/ρ(100K) values of about 3.7. Those films show, besides the initial fall-off just belowT _c , a further strong decrease ofR _s at low temperatures. This was observed both at 18.7 GHz and 87 GHz, as measured by a conventional cavity end plate replacement technique. ForT?T_c/2 these films exhibit an exp (?αT _c/T) dependence ofR _s withα-values around 0.4. These observations may be explained by a superconducting energy gap with 2Δ/kT _c≈0.8 for charge carriers localized in the CuO chains for YBa₂Cu₃O₇.     

Single-Step Synthesis of Sr4V2O6Fe2As2: The Blocking Layer Based Potential Future Superconductor

We report synthesis, structural details and transport measurements on Sr₄V₂O₆Fe₂As₂. Namely, the stoichiometric amounts of V₂O₅+1/2×SrO₂+7/2×Sr+2×FeAs are weighed mixed, ground thoroughly and palletized in rectangular form in a glove box in high purity Ar atmosphere. The pellet is further sealed in an evacuated (10^?5 torr) quartz tube and put for heat treatments at 750 and 1150°C in a single step for 12 and 36 hours respectively. Finally the quartz ampoule is allowed to cool naturally to room temperature. The as-synthesized sample is black in color. The compound crystallized in P4/nmm space group with lattice parameters a=b=3.925 Å and c=15.870 Å. Also seen are some small impurity lines. The compound did not exhibit superconductivity but instead a spin density wave (SDW) like metallic step at around 175 K is seen in R(T) measurements. Principally in [FeAs]^?1{Sr₄V₂O₆}^C[FeAs]^?1 the net value of blocking layer charge C must be either less or more than 2, to let it be electron or hole type superconductor respectively. Efforts are under way to achieve superconductivity in the studied system.     

Single crystals of In2Te5

Single crystals of semiconducting compound In₂Te₅ were grown by chemical transport employing iodine as a transport agent. The crystals had a plate-like habit with the [100] direction perpendicular to the flat surface of the platelets. Nominal dimensions are 10 × 1 × 0.05 mm. In₂Te₅ has a monoclinic structure with dimensions of the base centered cell: $\text{a}\text{= 13.47}\text{A}\text{?}$, $\text{b}\text{= 16.51}\text{A}\text{?}$, $\text{c}\text{= 4.365}\text{A}\text{?}$, β = 92°5′. The space group is $\text{C}{}_{\mathrm{<mtext>2</mtext><mtext>c</mtext>}}$. Pycnometric density is 5.96 g/cm³. The single crystals were all p-type. The conductivity, thermoelectric power and hardness were about 10^?5Ω^?1cm^?1, 650 mkV/°C, and 30 kg/mm², respectively. The minimum energy gap is 1.26 eV.     

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.     

Heat capacity and electrical resistivity of nickel in the range 1300–1700 K measured with a pulse heating technique

Measurements of the heat capacity and electrical resistivity of nickel in the temperature range 1300–1700 K by a subsecond duration pulse heating technique are described. The results are expressed by the relations: $$\begin{gathered} C_p = 21.735 + 9.8200 \times 10^{ - 3} T \hfill \\ \rho = 18.908 + 2.3947 \times 10^{ - 2} T \hfill \\ \end{gathered} $$ whereC _p is in J · mol^?1·K^?1,ρ is inμΩ·cm, andT is in K. Estimated maximum uncertainties in the measured properties are 3% for heat capacity and 1% for electrical resistivity.     

Research on the thermal decomposition and kinetics of byproducts from MgO wet flue gas desulfurization

This paper was aimed at the thermal decomposition and kinetics of the byproducts from MgO flue gas desulfurization. The effects of particle size and charcoal on thermal decomposition of the byproducts were investigated by the thermogravimetric analysis method, and the non-isothermal kinetic parameters of the byproducts were evaluated with the Coats–Redfern method. The results showed that the mass loss increased with the decrement of the particle size. However, the effect of the particle size on the mass loss of each thermal decomposition stage was different. Increasing the amount of charcoal powder in the byproducts had an obvious effect on the temperature characteristics of the thermal decomposition of magnesium sulfate, resulting in a reduced thermal decomposition temperature which could facilitate the thermal decomposition process. The equations G(α) = 1−(1−α)^1/2, G(α) = [−ln(1−α)]², and G(α) = 1−(1−α)^1/3 were the quite appropriate kinetic mechanisms describing the thermal decomposition process of MgCO₃, MgSO₃, and MgSO₄, respectively.     

The effect of microstructure on thermal expansion coefficients in powder-processed Al2Mo3O12

Orthorhombic Al₂Mo₃O₁₂ was investigated as a model anisotropic phase to understand the influence of powder preparation routes and bulk microstructure (mean grain size) on the bulk coefficient of thermal expansion (CTE) and to compare it to the intrinsic CTE of powder samples. A co-precipitation route was used for the synthesis of pure single-phase nanopowders, while a polyvinyl alcohol-assisted sol–gel method was utilized for the synthesis of micron-sized powders. Sintered samples prepared from both powders exhibited different microstructures in terms of mean crystal sizes and porosity. Bulk samples obtained from nanopowders were highly porous and contained crystals of approximately 100-nm diameter, while the bulk pieces produced from the micron-sized powders were denser, contained crystals larger than 5 μm, and showed occasional intergranular and transgranular microcracks. Such different microstructures hugely impact the bulk CTE: the nanometric sample possesses a bulk CTE (0.9 × 10^?6 °C^?1, from 200 to 700 °C) closer to the instrinsic CTE (2.4 × 10^?6 °C^?1) than for the micrometric sample, which showed a negative CTE (?2.2 × 10^?6 °C^?1) from 200 to 620 °C, and an even more negative CTE above 620 °C (?35 × 10^?6 °C^?1). A finite element analysis showed that the local maximum thermal tensile stresses could be as high as 220 MPa when simulating a temperature drop of 700 °C as an example of thermal treatment following sintering. This tensile stress is expected to exceed the tensile strength of Al₂Mo₃O₁₂, explaining the origin of microcracks in bulk samples prepared from the micron-sized powders. The thermal behavior of the microcracks leads to differences between the intrinsic and bulk thermal expansion; we show experimentally that such differences can be reduced by nanostructuring.     

Crystal structure, thermal expansion and electrical properties of a new compound Al0.33DyGe2

A new ternary compound Al_0.33DyGe₂ has been synthesized and studied from 298 K to773 K by means of X-ray powder diffraction technique. The crystal structural refinement of Al_0.33DyGe₂ has been performed by using the Rietveld method. The ternary compound Al_0.33DyGe₂ crystallizes in the orthorhombic of the defect CeNiSi₂-type structure (space group Cmcm, a = 0.41018(2)nm, b = 1.62323(6)nm, c = 0.39463(1)nm, Z = 4 and D_calc = 8.004 g/cm³). The average thermal expansion coefficients α_a, α_b and α_c of Al_0.33DyGe₂ are 1.96 × 10^− 5 K^− 1, 0.93 × 10^− 5 K^− 1 and 1.42 × 10^− 5 K^− 1, respectively. The bulk thermal expansion coefficient α_V is 4.31 × 10^− 5 K^− 1. The resistivity is observed to fall from 387 to 308 µΩ cm between room temperature and 25 K.     

A Simple Phenomenological Model for the Effective Kinematic Viscosity of Helium Superfluids

A number of experiments where quantum turbulence in helium superfluids has been generated by various means (such as towed/oscillating grids, thermal counterflow, pure superflow, spin-down, ion/vortex rings emission) displays a temporal decay of the observed vortex line density, of the power law form L=Γ t ^?3/2 at late times. The prefactor, Γ, in analogy with classical homogeneous isotropic turbulence, allows deducing the temperature dependent effective kinematic viscosity, ν_eff, for turbulent helium superfluids. It appears to be a robust quantity, independent of methods of generating quantum turbulence and detecting the decaying vortex line density. We present a simple phenomenological model to estimate ν_eff based on comparison of dissipation terms in equations of motion for classical viscous flow and vortex flow of a superfluid in a stationary normal fluid. This model leads to ν_eff≈κ q, where q=α/(1?α′); α and α′ being dimensionless mutual friction parameters. Within the temperature range where mutual friction dissipation mechanism is dominant this simple model prediction agrees well with the experimental data and with the recent theoretical estimate of Roche, Barenghi and Leveque (Europhys. Lett. 87:54006, 2009).     

Synthesis and study of Np(V) and Pu(V) benzoate complexes with bipyridine

Heteroligand compounds AnO₂(bipy)OOCC₆H₅ (An = Np, Pu; bipy = α,α-bipyridine, C¹⁰H⁸N²) were synthesized and studied. It follows from powder X-ray patterns that these compounds are isostructural. Their unit cell parameters, determined by indexing of the powder X-ray patterns, are as follows: a = 9.2162 (7), b = 10.2339(8), c = 17.4083(17) Å, and β = 96.48(1)° for Np and a = 9.1983(18), b = 10.2052(18), c = 17.370(3) Å and β = 96.51(1)° for Pu. The compounds crystallize in the monoclinic system space group P2₁/n, Z = 4. The electronic absorption spectra of crystalline compounds suggest pentagonal-bipyramidal surrounding of the central atom and the prescence of cation-cation bonds with AnO ₂ ⁺ ions acting as monodentate ligands with respect to each other. The IR spectra of the compounds were recorded, and their thermal behavior in air was studied.