Electric conductivity of nanocompounds based on polymer and chalcogenide semiconductors CdS,Cu<Subscript>2</Subscript>S

In this work, the temperature dependence of the specific surface resistances of composites on bases of gelatin with different contents of Cu₂S and CdS chalcogenide semiconductor nanoparticles is investigated. It is shown that nanocomposites have a posistor effect. It is found that the posistor effect is the result of the influence of intermolecular interactions at the polymer-nanoparticle phase interface and that the electrotransfer of charges in such systems is caused by tunneling through polymer layer between nanoparticles before the percolation threshold and flow theory after the percolation threshold.     

Influence of water vapor on the formation of pinning centers in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> upon low-temperature annealing

The influence of the double heat treatment (T = 300 and 930°С) on the critical parameters of highly textured YBa₂Cu₃O_6.96 and YBa₂Cu₃O_6.8 ceramics has been investigated. It has been shown that, upon low-temperature annealing in humid air, planar stacking faults are formed in these ceramics. These defects are partly retained after reduction annealing (at T = 930°С) and are efficient pinning centers in magnetic fields applied parallel and perpendicular to the c axis. Due to the absorption of water, the oxygen content is increased in the ceramics, which is accompanied by an increase in the critical temperature of superconducting transition up to 94 K for YBa₂Cu₃O_6.96 and up to 90 K for YBa₂Cu₃O_6.8. Optimal conditions of the double annealing have been established, after which the critical-current density increased to j _c ≥ 10⁴ А/сm² in an external magnetic field of up to 6 T. The low-temperature treatment in the neutral atmosphere saturated by water vapors deteriorates the current-carrying capacity of the highly textured ceramics, which is connected with the disappearance of texture due to the copper reduction and the precipitation of impurity phases.     

Effect of water intercalation on the structure and electrophysical properties of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6.9</Subscript>

The influence of water vapors and plastic deformation on the structure and electrophysical properties of YBa₂Cu₃O_6.9 (123) has been studied. It has been established that, at T = 200°C, the introduction of water into the structure of YBa₂Cu₃O_6.9 leads to its transition into a defect tetragonal phase of the 124 type as a result of the formation of planar stacking faults. After annealing at T = 930°C, these defects are partially retained and are efficient centers of pinning in the magnetic fields applied perpendicularly to the c axis, which makes it possible to increase (by an order of magnitude) the critical current density in the high-textured ceramics at 77 K in the external magnetic field of 5–10 T. The plastic deformation of the hydrated ceramics favors the reverse transition of the arising 124 phase to the 123 phase at T = 930°C and is accompanied by a recrystallization of the material, which leads to the appearance of a texture and an increase the critical current density.     

Electrical Conductivity of Nanocomposites Based on Low-Density Polyethylene and Cu<Subscript>2</Subscript>S Nanoparticles

The temperature dependences of the electrical conductivity of nanocomposites based on low-density polyethylene (LDPE) and Cu₂S nanoparticles are studied. It is shown that, starting from a certain temperature, the temperature dependence of the electrical conductivity is described by the following Arrhenius equation: σ = σ₀exp(–E/kT); the logσ = f(10³/T) dependence has several linear portions with different activation energy values. The observed behavior of the logρ = f(1/T) dependence of the LDPE/Cu₂S nanocomposites suggests that an increase in temperature is accompanied by an increase in the mobility of the structural units of the polymer matrix in the bulk and on the surface of the sample. The polymer–filler interfacial interactions decrease the electrical resistance of the boundary layer and thereby lead to a decrease in the activation energy of the charge carriers and an increase in the electrical conductivity of the nanocomposite.     

Microstructure properties and microhardness of rapidly solidified Al<Subscript>64</Subscript>Cu<Subscript>20</Subscript>Fe<Subscript>12</Subscript>Si<Subscript>4</Subscript> quasicrystal alloy

This paper presents differences in the microstructure and microhardness properties of conventional casting (ingot) and rapidly solidified Al₆₄Cu₂₀Fe₁₂Si₄ quasicrystal (QC) alloys. The phases present in the Al₆₄Cu₂₀Fe₁₂Si₄ ingot alloy were determined to be icosahedral quasicrystalline (IQC) Ψ-Al₆₅Cu₂₀Fe₁₅, cubic β-AlFe, tetragonal θ-Al₂Cu, and monoclinic λ-A1₃Fe₄ phases, whereas only IQC Ψ-Al₆₅Cu₂₀Fe₁₅ and cubic β-AlFe phases were identified in the rapidly solidified alloy. The microhardness value of the melt spun alloy was measured to be approximately 790 kg/mm². Microhardness increases with increasing solidification rates.     

Structure and properties of hydrogen-intercalated YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The effect of hydrogenation at 150 and 200°С on the structure and magnetic susceptibility of YBa₂Cu₃O_y (123) with different hydrogen contents has been studied. Upon the incorporation of hydrogen, the phase transition of the 123 phase into a defect tetragonal 124 phase occurs. In contrast to the transition upon hydration, the phase transition upon hydrogenation takes place only for compounds characterized by high oxygen contents (y > 6.5). Depending on the compound structure and oxygen content, hydrogen atoms can both occupy interstitials in Cu–O planes to form HYBa₂Cu₃O₆ and join with oxygen to form an oxide–hydroxide. In contrast to hydration, upon hydrogenation of YBa₂Cu₃O_y, the substitution of europium for yttrium and alloying with cerium and zirconium oxides do not block the intercalation of hydrogen into the structure of the 123 compound.     

Gas sensing properties of nano-crystalline SnO<Subscript>2</Subscript>-CuO compounds

We fabricated a micro gas sensor for hydrogen sulfide (H₂S) gas using MEMS technology and the sol-gel process, and synthesized SnO₂-CuO as a sensing material by the sol-gel method. Synthesized particles of SnO₂-CuO were characterized with an average particle size of about 40 nm as measured by FE-SEM imagery and XRD peaks. The sensing material was coated on the micro platform and annealed at 400 °C. The maximum gas sensitivity (R_s= R_g/R_a) was 0.005 at 300 °C for 1.0 ppm — H₂S. The gas sensitivity showed linear behavior with increasing H₂S concentration.     

Reaction diffusions of Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> and Cu<Subscript>3</Subscript>Sn intermetallic compound in the couple of Sn-3.5Ag eutectic solder and copper substrate

The growth kinetics of intermetallic compound layers formed between Sn-3.5Ag solder and Cu substrate were investigated as a consequence of solid-state isothermal aging. Isothermal aging was carried out in a temperature range between 70°C and 200°C for 0 to 60 days. A quantitative analysis of the intermetallic compound layer thickness as a function of time and temperature was performed. The diffusion couples showed a composite intermetallic layer comprised of Cu₆Sn₅ and Cu₃Sn. The growth of intermetallic compounds followed diffusion-controlled kinetics and the layer thickness reached only 9 μm after 60 day of aging at 150°C. The apparent activation energies were calculated for the growth of the total intermetallic compound (Cu₆Sn₅+Cu₃Sn); Cu₆Sn₅ and Cu₃Sn intermetallic are 65.4, 55.4 and 75.7 kJ/mol, respectively.     

Andreev reflections in a Bi<Subscript>1.8</Subscript>Pb<Subscript>0.3</Subscript>Sr<Subscript>1.9</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>x</Subscript> break junction

The current-voltage characteristic (CVC) of a break junction made from polycrystalline Bi_1.8Pb_0.3Sr_1.9Ca₂Cu₃O_x is investigated. The experimental CVC has a hysteretic feature that reflects part of the curve with a negative differential resistance. The CVC is discussed within the framework of the Kümmel-Gunsenheimer-Nicolsky theory that takes into account multiple Andreev reflections in superconductor/normalmetal/superconductor junctions.     

Dilatometric analysis of the process of the nanocrystallization of Fe<Subscript>72.5</Subscript>Cu<Subscript>1</Subscript>Nb<Subscript>2</Subscript>Mo<Subscript>1.5</Subscript>Si<Subscript>14</Subscript>B<Subscript>9</Subscript> soft magnetic alloy

The process of the nanocrystallization of magnetically soft Fe_72.5Cu₁Nb₂Mo_1.5Si₁₄B₉ alloy has been studied using dilatometry and thermomagnetic analysis, together with structural investigations. It has been shown that the amount of nanocrystalline phase precipitated upon heating of the amorphous precursor is in good agreement with a shortening of the ribbon length in the course of crystallization. Thermal expansion at the different stages of heating and cooling depends on the structural and phase states, as well as on the magnetic state of the alloy. The numerical value of the coefficient of linear thermal expansion decreases with an increase in the fraction of the ferromagnetic crystalline phase.     

Effect of Hydrogen Intercalation on the Structure of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> with a Low Oxygen Content

We used Raman spectroscopy to study the interaction of YBa₂Cu₃O_y (123) (y ≤ 6.5) with hydrogen at temperatures of 150–200°С. In contrast to the YBa₂Cu₃O_6.96 compound, compositions with low oxygen contents show a lower tendency to form stacking faults. We found that the hydrogenation of these compositions does not lead to the transformation of the 123 phase to the pseudo-124 phase. Absorbed hydrogen does not react with oxygen in 123 and does not form hydroxyl groups. The H_xYBa₂Cu₃O_y oxyhydride is the hydration-reaction product.     

Reaction Time and Film Thickness Effects on Phase Formation and Optical Properties of Solution Processed Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> Thin Films

Copper-zinc-tin-sulfide (Cu₂ZnSnS₄ or CZTS) is a promising p-type semiconductor material as absorber layer in thin film solar cells. The sulfides of copper and tin as well as zinc and sulfur powders were dissolved in hydrazine. The effect of chemical reaction between precursor species, at room temperature, was assessed for 6 to 22 h. For 22 h reaction time, the effect of spin coated film thickness on the resulting composition, after annealing under N₂ flow at 500 °C for 1 h, was investigated. The morphology, composition, and optical properties of the annealed films were determined by means of x-ray diffraction, scanning electron microscope, and spectrophotometer studies. It was found that, for less than optimal reaction time of 22 h or film thickness below 1.2 µm, other ternary phases namely Cu₄SnS₄, Cu₅Sn₂S₇, and ZnS co-exist in different proportions besides CZTS. Formation of phase-pure CZTS films also exhibited a tendency to minimize film cracking during annealing. Depending on the processing conditions, the band gap (E _g) values were determined to be in the range of 1.55 to 1.97 eV. For phase-pure annealed CZTS film, an increase in the E _g value may be attributed to quantum confinement effect due to small crystallite size.     

Structure and phase transformations in copper-alloyed rapidly melt-quenched Ni<Subscript>50</Subscript>Ti<Subscript>32</Subscript>Hf<Subscript>18</Subscript>-based alloys with high-temperature shape memory effect

Methods of transmission and scanning electron microscopy, chemical microanalysis, electron diffraction, and X-ray diffraction have been used to carry out the comparative study of the structure and chemical and phase composition of thin ribbons of four quasi-binary alloys (Ni₅₀Ti₃₂Hf₁₈, Ni₄₅Ti₃₂Hf₁₈Cu₅, Ni₃₅Ti₃₂Hf₁₈Cu₁₅, and Ni25Ti32Hf18Cu25) obtained in the amorphous state by rapid quenching from the melt by jet spinning. The critical temperatures of the devitrification and B2 ? B19′ martensitic transformation of the alloys have been determined based on the data of temperature dependences of the electrical resistivity. The specific features of the formation of the ultrafine-grained structure upon the devitrification and of the phase transformations have been studied depending on the heat-treatment regimes and chemical composition of the alloys (concentration of copper atoms).     

Temperature dependences of methane elution on a Cu<Subscript>3</Subscript>(BTC)<Subscript>2</Subscript> metal-organic framework

Methane elution from a helium flow was studied on a metal-organic framework Cu₃(BTC)₂ with gas chromatography under temperatures from 20 to 60°C. Specific retention volumes were calculated, and heat of adsorption was determined. The obtained values are characteristic for the microporous adsorbents having relatively large micropores and a low total volume of the micropores. The calculated efficiencies of an adsorbent layer alter slightly and their absolute values are significantly smaller than those of the activated carbons. Efficient kinetic constant has a parabolic dependence on temperature with a minimum at 40°C. Correctness of the developed algorithms to calculate elution constants on adsorbent layers of small length has been confirmed.     

Corrosion of Inconel 690 in N<Subscript>2</Subscript>-0.1%H<Subscript>2</Subscript>S gas at 700-800 °C

Inconel 690 superalloy was corroded at 700 °C and 800 °C for up to 70 h in N₂-0.1% H₂S gas. It corroded almost linearly with large weight gains, displaying little protectiveness. Its corrosion rates were quite fast when compared with its corrosion in air or Ar-1%SO₂ gas. The formed scales were thick, fragile, and nonadherent. They consisted primarily of Cr₂O₃ with some NiCr₂O₄, Ni₃S₂, CrS, and Cr₂S₃. The H₂S gas accelerated the corrosion significantly by forming nonprotective sulfides and dissolving hydrogen in the scale and in the internal corrosion zone that consisted of discrete chromium-sulfides and some oxide particles. The marker test indicated that the scales grew by the outward diffusion of metallic ions such as Ni, Cr, Fe, and Mn, whilst the internal corrosion zone thickened by the inward migration of oxygen and sulfur through the lattice, grain boundaries, and microcracks.     

Microstructure and Mechanical Behavior of Microwave Sintered Cu<Subscript>50</Subscript>Ti<Subscript>50</Subscript> Amorphous Alloy Reinforced Al Metal Matrix Composites

In the present work, Al metal matrix composites reinforced with Cu-based (Cu₅₀Ti₅₀) amorphous alloy particles synthesized by ball milling followed by a microwave sintering process were studied. The amorphous powders of Cu₅₀Ti₅₀ produced by ball milling were used to reinforce the aluminum matrix. They were examined by x-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness and compression testing. The analysis of XRD patterns of the samples containing 5 vol.%, 10 vol.% and 15 vol.% Cu₅₀Ti₅₀ indicates the presence of Al and Cu₅₀Ti₅₀ peaks. SEM images of the sintered composites show the uniform distribution of reinforced particles within the matrix. Mechanical properties of the composites were found to increase with an increasing volume fraction of Cu₅₀Ti₅₀ reinforcement particles. The hardness and compressive strength were enhanced to 89 Hv and 449 MPa, respectively, for the Al-15 vol.% Cu₅₀Ti₅₀ composites.     

Effect of Titanium Additions on the Thermophysical Properties of Glass-Forming Cu<Subscript>50</Subscript>Zr<Subscript>50</Subscript> Alloy

Differential scanning calorimetry, laser flash method, and dilatometry were used to study the thermophysical properties of quenched Cu₅₀Zr_50–xTi_x (x = 0, 2, 4, 6, 8) alloys in the temperature range from room temperature to 1100 K. Data obtained on the heat capacity, thermal diffusivity, and density have been used to calculate the coefficient of thermal conductivity. Temperatures corresponding to the stability of martensite CuZr phase, its eutectoid decomposition, and formation in Cu₅₀Zr_50–xTi_x alloys with different Ti contents upon heating have been determined. It has been found that the thermal diffusivity and thermal conductivity of the studied alloys are low and a typical of metallic systems. As the titanium content increases, the coefficients of thermal conductivity and thermal diffusivity vary slightly. It has been shown that the low values of thermophysical characteristics correspond to the better capability of amorphization and can be a criterion for the glass-forming ability of Cu–Zr-based alloys.     

Effect of hydrogen intercalation on the critical parameters of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The effect of hydrogenation at T = 150 and 200°C on the electrophysical properties of highly textured YBa₂Cu₃O _y ceramics with different oxygen content has been investigated. Like hydration, hydrogenation results in the deterioration of these properties. However, in samples with high oxygen contents (y = 6.96) hydrogenated at T = 150°C after oxidation (400°C) or recovery annealing with subsequent oxidation, the critical current density and first critical field increase compared to the initial state. The improvement of the properties occurs mainly in a magnetic field applied perpendicularly to the c axis. As after hydration, this is connected with the formation of planar defects in the course of low-temperature annealing. In addition, in the process of the hydrogenation, the partial reduction of copper occurs with the formation of microinclusions of Cu₂O and other products of chemical decomposition, which are extra pinning centers of magnetic vortices.     

Effects of cryogenic treatment on the thermal physical properties of Cu<Subscript>76.12</Subscript>Al<Subscript>23.88</Subscript> alloy

The thermal diffusion coefficient,heat capacity,thermal conductivity,and thermal expansion coefficient of Cu76.12Al23.88 alloy before and after cryogenic treatment in the heating temperature range of 25°C to 600°C were measured by thermal constant tester and thermal expansion instrument.The effects of cryogenic treatment on the thermal physical properties of Cu76.12Al23.88 alloy were investigated by comparing the variation of the thermal parameters before and after cryogenic treatment.The results show that the variation trend of the thermal diffusion coefficient,heat capacity,thermal conductivity,and thermal expansion coefficient of Cu76.12Al23.88 alloy after cryogenic treatment was the same as before.The cryogenic treatment can increase the thermal diffusion coefficient,thermal conductivity,and thermal expansion coefficient of Cu76.12Al23.88 alloy and decrease its heat capacity.The maximum difference in the thermal diffusion coefficient between the before and after cryogenic treatment appeared at 400°C.Similarly,thermal conductivity was observed at 200°C.