Temperature-dependent thermal expansion of cast and hot-pressed LAST (Pb–Sb–Ag–Te) thermoelectric materials

The thermal expansion for two compositions of cast and hot-pressed LAST (Pb–Sb–Ag–Te) n-type thermoelectric materials has been measured between room temperature and 673 K via thermomechanical analysis (TMA). In addition, using high-temperature X-ray diffraction (HT-XRD), the thermal expansion for both cast and hot-pressed LAST materials was determined from the temperature-dependent lattice parameters measured between room temperature and 623 K. The TMA and HT-XRD determined values of the coefficient of thermal expansion (CTE) for the LAST compositions ranged between 20 × 10^?6 K^?1 and 24 × 10^?6 K^?1, which is comparable to the CTE values for other thermoelectric materials including PbTe and Bi₂Te₃. The CTE of the LAST specimens with a higher Ag content (Ag_0.86Pb₁₉Sb_1.0Te₂₀) exhibited a higher CTE value than that of the LAST material with a lower Ag content (Ag_0.43Pb₁₈Sb_1.2Te₂₀). In addition, a peak in the temperature-dependent CTE was observed between room temperature and approximately 450 K for both the cast and hot-pressed LAST with the Ag_0.86Pb₁₉Sb_1.0Te₂₀ composition, whereas the CTE of the Ag_0.43Pb₁₈Sb_1.2Te₂₀ specimen increased monotonically with temperature.     

Structural evolution of ZrO2–mullite nanocomposites from the Si–Al–Zr–O amorphous bulk

ZrO₂–mullite nanocomposites were fabricated by in-situ-controlled crystallization of Si–Al–Zr–O amorphous bulk at 800–1250°C. The structural evolution of the Si–Al–Zr–O amorphous, annealed at different temperatures, was studied by X-ray diffraction, infrared, Laser Raman spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The materials consisted of an amorphous phase up to 920°C at which phase separation of Si-rich and Al, Zr-rich clusters occurred. The crystalline phases of t-ZrO₂ and mullite were observed at 950°C and 1000°C, respectively. Mullite with a tetragonal structure, formed by the reaction between Al–Si spinel and amorphous silica at low temperature, changed into an orthorhombic structure with the increase of temperature. It was the phase segregation that improved crystallization of the Si–Al–Zr–O amorphous bulk. The anisotropic growth of mullite was observed and the phase transformation from t-ZrO₂ to m-ZrO₂ occurred when the temperature was higher than 1100°C.     

Aerogel–copper nanocomposites prepared using the adsorption of a polyfluorinated complex from supercritical CO2

A supercritical deposition method has been used to synthesize aerogel?Ccopper nanocomposites. Carbon, resorcinol?Cformaldehyde, and silica aerogels (CAs, RFAs, and SAs) were impregnated with a new polyfluorinated copper precursor (CuDI6), which has a high solubility in supercritical carbon dioxide (scCO₂). Adsorption isotherms of CuDI6 onto various aerogels from scCO₂ were determined at 35?°C and 10.6?MPa using a batch method which is based on the measurement of the fluid phase concentration. The relative affinity between CuDI6 and different aerogels changed in the following order: CA?>?RFA?>?SA. The effect of temperature on the adsorption isotherms for the CuDI6?CCO₂?CCA system was also studied at 35 and 55?°C and at a CO₂ density of 736.1?kg/m³. The CuDI6 uptake at a particular CuDI6 concentration increased with increasing temperature. Adsorbed CuDI6 was found to convert into Cu and Cu/Cu₂O nanoparticles on the aerogel supports after chemical or thermal treatments at ambient pressure and at temperatures ranging from 200 to 400?°C.     

Goos–Hänchen shifts of a light beam reflected from the interface of colloidal ferrofluids

Controllable Goos–Hänchen shift of a light beam reflected from the colloidal ferrofluids is investigated by using the stationary-phase method. It is found that the Goos–Hänchen shift can be easily controlled by the local H_e factor and the volume factor. Using this scheme, the peak value, the peak position and the width of the Goos–Hänchen shift can all be controlled by adjusting the external magnetic field for a fixed configuration, which also provides a possibility for obtaining larger negative Goos–Hänchen shift by changing the external controlling field. Our results have potential applications in optical devices.     

Reduction of the Bethe–Salpeter wave function: Fermion–scalar case and scalar–scalar case

In this paper, the general forms of the nonrelativistic Bethe–Salpeter wave functions for fermion–scalar bound state and scalar–scalar bound state are presented. Using the obtained normalization conditions and the corresponding Schrödinger equations for these bound states, the nonrelativistic Bethe–Salpeter wave functions can be calculated and can be used to compute the amplitude for the process involving these bound states.     

Effect of SnI2 on the thermal and optical properties of Ge–Se–Te glasses

A systematic series of (Ge₂₀Se₁₅Te₆₅)_1?x–(SnI₂)_x (x = 0, 0.05, 0.1, 0.15) chalcogenide glasses have been prepared. The amorphous nature can be confirmed by XRD and SEM. With the SnI₂ content increasing, the indirect optical band gaps are decreased from 0.662 to 0.622 eV according to Tauc laws. The introduction of SnI₂ makes the glasses much easier to prepare and more stable against crystallization, making them drawable as optical fibers. The highest ΔT (130 °C) value for (Ge₂₀Se₁₅Te₆₅)_0.9–(SnI₂)_0.1 glass composition can be obtained. A slight red-shifting of the long-wavelength cutting-off edge from 18.4 to 19.4 μm was shown and it seems that SnI₂ in these glasses offers the improvement in the far-infrared properties.     

Improving metal-enhanced photoluminescence by micro-pattern of metal nanoparticles: a case study of Ag–ZnCdO system

Micro-pattern of Ag nanoparticles and Ag film is inserted between ZnCdO film and the substrate to enhance the photoluminescence (PL) of ZnCdO films, achieving enhancement ratio of 21.2 and 7.1, respectively. Time-resolved photoluminescence shows that the PL lifetime of Ag/ZnCdO films is longer than that of bare ZnCdO, which is attributed to surface modification and surface plasmons coupling. The improved enhancement in the sample with Ag pattern is attributed to the fact that periodic Ag structure offers additional scattering mediums and thus increases the light extraction efficiency.     

Synthesis of rGO–Ag nanoparticles for high-performance SERS and the adsorption geometry of 2-mercaptobenzimidazole on Ag surface

The sliver nanoparticles (AgNPs) with diameters of 30～50 nm were self-assembled onto the surfaces of reduced graphene oxide (rGO) sheets simply by mixing AgNO₃ aqueous solution and GO dispersion via a synchronous reduction process. Structure and morphology of the rGO–AgNPs hybrids were well characterized. More significantly, the surface-enhanced Raman scattering (SERS) spectrum of 2-mercaptobenzimidazole (MBI) adsorbed on the solid rGO–AgNPs surface shown that the rGO–AgNPs system gives a very strong SERS intensity at in-plane vibrational modes in comparison to the out-of-plane vibrational modes. This large enhancement effect is most likely a result of charge-transfer (CT) mechanism. Based on the surface selection rules and the information provided by the highly enhanced in-plane vibrational modes, it can be found that MBI molecule was adsorbed on AgNPs surface as a thiol form via the sulphur and nitrogen atoms with a slightly tilted geometric conformation.     

Novel Ag–BaTiO3/PVDF three-component nanocomposites with high energy density and the influence of nano-Ag on the dielectric properties

Novel Ag–BaTiO₃/PVDF (polyvinylidene fluoride) three-component nanocomposites and traditional BaTiO₃/PVDF two-component nanocomposites were prepared by the same procedures. The dielectric properties of these two kinds of composites were compared. The results showed that the kind of three-component nanocomposites had better dielectric properties. The energy density of such kind of composites could reach nearly 10 J/cm³, which indicated that these nanocomposites could be used as the dielectric layers of pulse-power capacitors. The Coulomb blockade effect was used to explain the dielectric breakdown properties and the resistivities under high electric field of such new kind of nanocomposites.     

Gluon distribution function from the Berger–Block–Tan form of the structure function F 2

Physics of Atomic Nuclei - We present a set of formulas to extract the gluon distribution function from the Berger–Block–Tan form of the deep inelastic structure function F 2 and its...     

Self-absorption quantification in the case of SF6–N2 thermal plasma mixture

A simple and accurate method is presented to estimate quantitatively the self-absorption effect for the emission radiations from nitrogen in the case of SF₆–N₂ plasma mixture. The self-absorption phenomena of optically thick lines are treated parametrically on the basis of escape factor. The resonance escape factors for bound–bound transitions for the lines emitted by atomic nitrogen at 113.5, 119.96, 124.32, 149.26 and 174.53 nm are calculated assuming Voigt line shape. The escape factors for free-bound (continuum) radiation which have been the object of fewer investigations are also considered. The escape factors are calculated as a result of the solutions of the equation of radiative transfer which is independent from any special geometry. Assuming a constant plasma size the dependence of escape factors on the temperature, pressure and the nitrogen proportion in SF₆ plasma are also taken into account. These calculations may be useful in plasma modeling and diagnostics as well as the application of laser-induced plasma spectroscopy (LIPS) used in the quantitative analysis of elemental compositions.     

Effect of Coulomb blockade on the switching time of Ag–Ag2S–Pt atomic switches

A theoretical model based on the single electron tunneling phenomenon is employed to calculate the time-dependent electrical resistance of an Ag–Ag₂S–Pt atomic switch at different applied voltages. While a negative voltage is applied to Pt electrode, Ag atoms precipitate on the surface of Ag₂S electrode where they form Ag clusters. The resistance of switch decreases as Ag clusters grow larger between two electrodes. Our model calculations imply the time required to decrease the resistance of switch below the resistance quantum (switching time) is mainly determined by the Coulomb blockade effect of Ag clusters. The switching time is found to decrease exponentially with increasing the applied voltage, which agrees very well with the experimental observations.     

Core–shell nanostructures and nanocomposites of Ag@TiO2: effect of capping agent and shell thickness on the optical properties

Two different shell-forming reagents viz. titanium isopropoxide and titanium hydroxyacylate, have been employed to obtain core–shell nanostructures of Ag@TiO₂. However, nanocomposites were formed when the shell-forming agent, titanium isopropoxide, was added before breaking the micelles. Titanium hydroxyacylate has been used for the first time as a shell-forming agent which resulted in uniform core–shell structures of Ag@TiO₂ with core diameter ranging from 10 to 40 nm and a shell thickness of 10–50 nm. The low rate of hydrolysis of titanium hydroxyacylate than titanium isopropoxide (used in other methods) appears to be responsible for the uniform shell thickness. The presence of capping agent (2-mercaptoethanol) disrupts the formation of a uniform shell structure of Ag@TiO₂. HRTEM, IR, and XPS studies of Ag@TiO₂ synthesized using capping agent show the formation of Ag₂S coated with an amorphous layer of TiO₂. A red shift of 25 and 10 nm was observed in the surface plasmon band of silver for Ag@TiO₂ core–shell structures (compared with that of silver nanoparticles) synthesized using titanium hydroxyacylate and titanium isopropoxide, respectively. The presence of capping agent (2-mercaptoethanol) masks the surface plasmon peak. Photoluminescence studies show an increase in the emission intensity for the core–shell structures when compared to that of TiO₂ nanoparticles.     

Solutions of the Yang–Baxter equation: Descendants of the six-vertex model from the Drinfeld doubles of dihedral group algebras

The representation theory of the Drinfeld doubles of dihedral groups is used to solve the Yang–Baxter equation. Use of the two-dimensional representations recovers the six-vertex model solution. Solutions in arbitrary dimensions, which are viewed as descendants of the six-vertex model case, are then obtained using tensor product graph methods which were originally formulated for quantum algebras. Connections with the Fateev–Zamolodchikov model are discussed.