Effect of some metallic additives (Ag, Cd, and Sn) on thermal transport properties of a-Se

In this study, we have studied the effect of elements Ag, Cd, and Sn as chemical modifiers on some thermal transport properties (thermal conductivity, diffusivity, and specific heat per unit volume) of amorphous Se. Concurrent measurements of thermal transport properties such as effective thermal conductivity (??_e), thermal diffusivity (??_e), and specific heat per unit volume (??C _v) are used at room temperature for twin pellets of pure Se- and Se-based binary Se₉₈M₂ (M?=?Ag, Cd, and Sn) alloys using transient plane source technique. We have also determined the thermal inertia I _T using the experimental values of thermal conductivity and specific heat per unit volume for present amorphous alloys. The increasing sequence of measured thermal transport properties is also discussed.     

Comparative analysis of some thermo-physical properties of Se90Zn10 and Te90Zn10 alloys

The present paper reports a comparative study of some thermo-physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of Se₉₀Zn₁₀ and Te₉₀Zn₁₀ alloys. Simultaneous measurements of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of twin pellets of Se₉₀Zn₁₀ and Te₉₀Zn₁₀ alloys using transient plane source (TPS) technique have been made at room temperature. From the measured values of λ_e and χ_e, the specific heat per unit volume (C_v) has been calculated. The results indicate that the measured values of these parameters are higher for Te₉₀Zn₁₀ alloy as compared to Se₉₀Zn₁₀ alloy. This is explained in terms of thermal conductivity of chalcogen elements Se and Te.     

Effect of indium additive on thermal transport properties of Se–Te–Cd multi-component chalcogenide glasses

The thermal conductivity, thermal diffusivity and specific heat per unit volume of twin pellets of Se₇₅Te_15?Cx Cd₁₀In _x (x?=?0, 5, 10 and 15) glasses, were carried out at room temperature by transient plane source technique. Results indicated that both values of thermal conductivity (??) and thermal diffusivity (??) are varied with In (indium) content and highest for 5?at.% of In, whereas the specific heat per unit volume is almost constant with increase of indium concentration. This shows that Se₇₅Te₁₀Cd₁₀In₅ glass can be considered as a critical composition at which the alloy becomes chemically ordered and most thermally stable than other compositions. This compositional dependence behaviour of thermal conductivity and thermal diffusivity can explained in terms of iono-covalent type bond which In makes with Se and Te as it is incorporated in Se?CTe?CCd glasses.     

Effect of Bi incorporation on the glass transition kinetics of Se<Subscript>85</Subscript>Te<Subscript>15</Subscript> glassy alloy

Bulk samples of Se_85-xTe₁₅Bi_x glassy alloys are obtained by melt quenching technique. Differential scanning calorimetry has been applied to determine the thermal properties of Se-rich Se_85-xTe₁₅Bix glassy alloys at different heating rates. The glass transition temperature (T _g) is found to shift to a higher temperature with increasing heating rate and with Bi addition. Activation energy and fragility of the system is also calculated. Specific heat is evaluated and a jump in heat capacity is observed at T _g. Theoretical parameters viz; density, molar volume, number of atoms per unit volume, lone pair electrons and cohesive energy of the system are also reported.     

Determination of effective diffusion coefficients in calcium alginate gel plates with varying yeast cell content

Effective diffusion coefficients (D_e) have been determined for lactose, glucose, galactose, and ethanol in calcium alginate gel with varying yeast cell concentration. The measurements have been performed in a diffusion cell, and the results evaluated with the quasisteady-state method. An ultrasonic meter was used for gel thickness determination with an accuracy of 1.5% and a new method for the reproducible preparation of gel plates was developed. It was found thatD _e in pure alginate gel decreased to about 90% of the diffusivity in water and did not vary with alginate concentration.D _e decreased considerably with increasing yeast cell concentration. For the solutes studied, the effective diffusion coefficient can be estimated according to the equationD _e =D _eo (1 - ?)/[1+(?/2)], whereD _eo is the effective diffusivity in pure gel and ? is the volume fraction of yeast cells.     

Specific heat studies in a-Se and a-Se<Subscript>90</Subscript>M<Subscript>10</Subscript> (M = In,Sb, Te) alloys

Specific heat measurements have been made in a-Se and a-Se₉₀M₁₀ (M = In, Sb, Te) alloys using differential scanning calorimetry (DSC) technique to see the effect of additives In, Sb and Te on the specific heat in a-Se. An extremely large increase in the specific heat values has been observed at the glass transition temperature. It has also been found that the values of C _p below glass transition temperature (C _pg ) and after glass transition (C _pe ) are highly composition dependent. This indicates that the additives used in the present study influences the structure of the a-Se. Specific heat and atomic mass values of the additive elements are found to be significant for the explanation of present results.     

Thermal conductivity and heat capacity of liquid and glassy poly(vinyl acetate) under pressure

The dependence of thermal conductivity λ and heat capacity per unit volume pc_p on temperature and pressure for poly(vinyl acetate) has been measured by a transient hot-wire probe technique. The measurements were made under pressures up to 0.5 GPa over a temperature range of 270–470 K. The temperature coefficient of thermal conductivity (? lnλ/?T)_p was found to increase with pressure for both the liquid and the glassy state. The change in heat capacity per unit volume in the region of the glass-transition temperature was found to decrease with increasing pressure. The Ehrenfest relation does not explain the variation of the pressure coefficient of the glass-transition temperature.     

Controllable Synthesis of Bandgap‐Tunable CuSxSe1−x Nanoplate Alloys

Composition engineering is an important approach for modulating the physical properties of alloyed semiconductors. In this work, ternary CuS_xSe_1?x nanoplates over the entire composition range of 0≤x≤1 have been controllably synthesized by means of a simple aqueous solution method at low temperature (90 °C). Reaction of Cu²⁺ cations with polysulfide/‐selenide ((S_nSe_m)^2?) anions rather than independent S_n^2? and Se_m^2? anions is responsible for the low‐temperature and rapid synthesis of CuS_xSe_1?x alloys, and leads to higher S/Se ratios in the alloys than that in reactants owing to different dissociation energies of the Se?Se and the S?S bonds. The lattice parameters ‘a’ and ‘c’ of the hexagonal CuS_xSe_1?x alloys decrease linearly, whereas the direct bandgaps increase quadratically along with the S content. Direct bandgaps of the alloys can be tuned over a wide range from 1.64 to 2.19 eV. Raman peaks of the S?Se stretching mode are observed, thus further confirming formation of the alloyed CuS_xSe_1?x phase.     

Effects of Se doping on thermoelectric properties of Zn4Sb3 at low-temperatures

The thermoelectric properties of Se-doped compounds Zn₄(Sb_1?xSe_x)₃ (x = 0, 0.005, 0.01, 0.015) have been studied. The results indicate that low-temperature (T < 300 K) thermal conductivity of moderately doped Zn₄(Sb_0.99Se_0.01)₃ reduce remarkably as compared with that of Zn₄Sb₃ due to enhanced impurity (dopant) scattering of phonons. Electrical resistivity and Seebeck coefficient are found to increase and then decrease moderately with the increase in the Se content. Moreover, the lightly doped compound Zn₄(Sb_0.99Se_0.01)₃ exhibits the best thermoelectric performance due to the improvement in both its thermal conductivity and Seebeck coefficient. Its figure of merit, ZT, is about 1.3 times larger than that of pure Zn₄Sb₃ at 300 K.     

Glass-forming ability and thermal stability of Se<Subscript>100−x</Subscript>(Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript>)<Subscript>x</Subscript> glassy alloys

Glassy Se_100?x(Ge₂Sb₂Te₅)_x (x?=?5, 10, 15 and 20) bulk alloys were prepared by melt-quenched technique and studied by using differential scanning calorimetry at different heating rates under non-isothermal condition. The detailed thermal analysis shows that the glass transition temperature (T_g) depends on heating rates and x content. In particular, it is found that the glass-forming ability, thermal stability (T_c???T_g) and crystallization activation energy (E_c) increase with increased x content in amorphous Se, whereas glass transition activation energy (E_g) and fragility index (F) decrease with increased x contents. Variation in these parameters can be explained on the basis of network-forming ability of Se and bonding arrangement among the constituent atoms of alloys.     

Evaluation of sorption and diffusion behavior of selenium in crushed granite by through-diffusion column tests

Distribution coefficients (K _d), apparent diffusion coefficients (D _a) and retardation factor (Rf) in this work obtained by batch and through-diffusion experiments have been performed, respectively. The accumulative concentration method developed by Crank (The mathematics of diffusion, 12) was applied to realize apparent and effective diffusion coefficient (D _a and D _e) of Se. Besides, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (K _d) obtained by batch tests in 14 days under aerobic and anaerobic systems were 6.98 ± 0.35 and 5.21 ± 0.25 mL/g. Moreover, Rf^cal and K _d ^cal of Se obtained from accumulative concentration’s method in through-diffusion test showed an obvious discrepancy with the increase of length/diameter (L/D) ratio. However, it presented an agreement of Rf^H/Se and K _d ^H/Se in a various L/D ratio by comparison of apparent diffusion coefficient’s (D _a) between HTO and Se. It appears that the Rf^H/Se and K _d ^H/Se obtained from the through-diffusion experiments are lower than those derived from the batch experiments. Therefore, it demonstrates that reliable Rf and K _d of Se by through-diffusion experiments could be achieved at a non-reactive radiotracer (HTO) prior to tests and will be more confident in long-term performance assessment of disposal repository.     

Thermoelectric properties of Ag-doped n-type (Bi2Te3)0.9-(Bi2−xAgxSe3)0.1 (x=0-0.4) alloys prepared by spark plasma sintering

Ag-doped n-type (Bi₂Te₃)_0.9-(Bi_2−xAg_xSe₃)_0.1 (x=0-0.4) alloys were prepared by spark plasma sintering and their physical properties evaluated. When at low Ag content (x=0.05), the temperature dependence of the lattice thermal conductivity follows the trend of (Bi₂Te₃)_0.9-(Bi₂Se₃)_0.1; while at higher Ag content, a relatively rapid reduction above 400 K can be observed due possibly to the enhancement of scattering of phonons by the increased defects. The Seebeck coefficient increases with Ag content, with some loss of electrical conductivity, but the maximum dimensionless figure of merit ZT can be obtained to be 0.86 for the alloy with x=0.4 at 505 K, about 0.2 higher than that of the alloy (Bi₂Te₃)_0.9-(Bi₂Se₃)_0.1 without Ag-doping.     

Etude thermodynamique du systeme plomb—selenium par calorimetrie

The enthalpy of formation of PbSe liquid alloys was measured at nine temperatures by direct reaction calorimetry (drop method) for 0 < x_Se < 0.5 and 883 < T < 1365 K. The enthalpy of formation is strongly negative in the whole range investigated. It is not dependent on the temperature when x_Se < 0.3 but increases strongly with temperature when 0.3 < x_Se < 0.5 (ΔC_p,max ?90 J K^?1 mol^?1 at x_Se = 0.5).     

Magnetische Messungen in den Systemen Co—Se,Ni—Se und Co—Ni—Se

The magnetic behavior of the binary systems Co?Se and Ni?Se was investigated within the temperature region from 100 to 300 K. Both phases Co_1?x Se and CoSe₂ behave like antiferromagnetics following theCurie-Weiss law with magnetic moments between 2.22 and 3.16 μ_B. For the corresponding phases Ni_1?x Se and NiSe₂ the results indicate a feeblePauli paramagnetism. For some alloys a slight positive temperature coefficient could be observed. Three quasibinary sections of the ternary phase (Co_1?y Ni _y )_1?x Se and one section of (Co_1?y Ni _y )Se₂ were investigated in the ternary system Co?Ni?Se. For all sections the increase of the Ni-content resulted in a continuous shift fromCurie-Weiss behavior toPauli paramagnetism. Due to the change from negative to positive temperature coefficients some ternary alloys have a temperature-invariant paramagnetism.     

Study of glass transition kinetics of selenium matrix alloyed with up to 10% indium

Glassy selenium matrix alloyed with up to 10% indium, namely Se_0.95In_0.05 and Se_0.9In_0.1, was prepared by the melt quenching technique. Differential thermal analysis (DTA) has been used to study the glass transition kinetics of the two binary Se–In alloys in comparison with that of pure Se. DTA scans were recorded at different constant heating rates (β = 1:20 °/min). The glass transition temperature (T _g) is found to be shifting to a higher value with increasing of both β and In-content. Such a configurationally response is related to the observed increase of the stability parameters accompanied with the introduction of In into the Se matrix. The activation energy of glass transition (E _g) has been determined using two different non-isothermal models (Moynihan and Kissinger) where a good coincidence is obtained. The compositional dependence (0:10% In) of all considered parameters is discussed in terms of the introduced structural matrix.     

Temperature dependence of the thermophysical properties of polycrystallene chalcogenide glasses

The specific heat (C _p), thermal conductivity (λ), thermal diffusivity (a), and electrical conductivity (σ) were measured for polycrystalline HgS and Sb₂S₃ in the temperature range 300–600 K. The measurements were performed with an experimental apparatus based on a socalled flash method. The results showed that the mechanism of heat transfer is mainly due to phonons, whereas the contribution of electrons and bipolars is very small indeed. The energy gap of the samples was also calculated.     

Glass transition and crystallization kinetics analysis of Sb–Se–Ge chalcogenide glasses

Differential thermal analysis (DTA) has been employed to investigate the effect of Ge addition on the glass transition behavior and crystallization kinetics of Sb₁₀Se_90?xGe_x (x = 0, 19, 21, 23, 25, 27) alloys. The three characteristic temperatures viz. glass transition (T _g), crystallization (T _c), and melting (T _m) have been determined and found to vary with the heating rates and Ge content. Thermal stability and glass forming tendency have been evaluated in terms of ΔT (= T _c ? T _g) and reduced glass transition temperature. The activation energies for glass transition and crystallization have been used to analyze the nucleation and growth process. The activation energy analysis also determines the suitability of alloys to be used in switching applications. Results have been interpreted in terms of bond energies and structural transformations in the investigated alloys.     

A New Synthetic Methodology in the Preparation of Bimetallic Chalcogenide Clusters via Cluster-to-Cluster Transformations

A decanuclear silver chalcogenide cluster, [Ag₁₀(Se){Se₂P(OⁱPr)₂}₈] (2) was isolated from a hydride-encapsulated silver diisopropyl diselenophosphates, [Ag₇(H){Se₂P(OⁱPr)₂}₆], under thermal condition. The time-dependent NMR spectroscopy showed that 2 was generated at the first three hours and the hydrido silver cluster was completely consumed after thirty-six hours. This method illustrated as cluster-to-cluster transformations can be applied to prepare selenide-centered decanuclear bimetallic clusters, [Cu_xAg_10-x(Se){Se₂P(OⁱPr)₂}₈] (x = 0–7, 3), via heating [Cu_xAg_7−x(H){Se₂P(OⁱPr)₂}₆] (x = 1–6) at 60 °C. Compositions of 3 were accurately confirmed by the ESI mass spectrometry. While the crystal 2 revealed two un-identical [Ag₁₀(Se){Se₂P(OⁱPr)₂}₈] structures in the asymmetric unit, a co-crystal of [Cu₃Ag₇(Se){Se₂P(OⁱPr)₂}₈]_0.6[Cu₄Ag₆(Se){Se₂P(OⁱPr)₂}₈]_0.4 ([3a]_0.6[3b]_0.4) was eventually characterized by single-crystal X-ray diffraction. Even though compositions of 2, [3a]_0.6[3b]_0.4 and the previous published [Ag₁₀(Se){Se₂P(OEt)₂}₈] (1) are quite similar (10 metals, 1 Se²⁻, 8 ligands), their metal core arrangements are completely different. These results show that different synthetic methods by using different starting reagents can affect the structure of the resulting products, leading to polymorphism.     

Synthese und Kristallstruktur von [Na(12-Krone-4)2]2[Hg(Se4)2] · 1,5 DMF

Synthesis and Crystal Structure of [Na(12-Crown-4)₂]₂[Hg(Se₄)₂] · 1.5 DMF . The title compound has been prepared by the reaction of Na₂Se₄ with mercury acetate in DMF solution in the presence of 15-crown-5, forming dark red crystal needles. [Na(12-crown-4)₂]₂[Hg(Se₄)₂] · 1.5 DMF crystallizes in the space group C2/c with eight formula units per unit cell. The structure was determined with 3 824 observed unique reflections, R = 0.085. Lattice dimensions at - 70°C: a = 2 884(2), b = 1 407.7(7), c = 2 843(2) pm, β = 93.93(5)°. The structure consists of [Na(12-crown-4)₂]⁺ ions with a sandwichlike coordination of the crown ether molecules, and of [Hg(Se₄)₂]^2? ions, in which the mercury atom is coordinated by two tetraselenido ions in a chelating fashion. The [Hg(Se₄)₂]^2? ions are arranged to infinite chains via Se…?Se contacts.     

Preparation of the HgCr2(SexS1−x)4 type compounds and the X ray control of the process of formation of their spinel structures

Compounds of the HgCr₂(Se_xS_1?x)₄ type were prepared for 0.750 ? x ? 0.250 by thermal synthesis from parent elements. Individual reaction stages were controlled röntgenographically. The values of electrical conductivity activation energy of the compounds have been calculated and chemical analyses of the substances prepared have been developed.