A cooled,intense polarized hydrogen atomic beam for the ETH polarized ion source

A slow (35 K) atomic beam with I⩾10¹⁷ atoms s⁻¹ and n_H∼2×10¹² atoms cm⁻³ has been developed. On the ETH polarized ion source, DC intensities of 0.4 mA for positive and 16 μA for negative ions have been observed.     

Supercapacitive performance of hydrous ruthenium oxide (RuO2 · nH2O) thin films synthesized by chemical route at low temperature

In the present investigation, we report the synthesis of ruthenium oxide (RuO₂ · nH₂O) thin films by simple chemical bath deposition (CBD) method at low temperature on the stainless steel substrate. The prepared thin films are characterized for their structural and morphological properties by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT–IR) and scanning electron microscopy (SEM). The structural study revealed that the ruthenium oxide thin films are amorphous. Scanning electron microscopy study shows compact morphology with small overgrown particles on the surface of the substrate. FT–IR study confirms the formation of RuO₂ · nH₂O material. The supercapacitor behaviour of RuO₂ · nH₂O thin film was studied using cyclic voltammetry (CV) technique in 0 · 5 M H₂SO₄electrolyte. RuO₂ · nH₂O film showed maximum specific capacitance of 192 F · g^{? 1}at a scan rate of 20 mV · s^{? 1}. The charge–discharge studies of RuO₂ · nH₂O carried out at 300 μA · cm^{? 2}current density revealed the specific power of 1 · 5 kW.kg^{? 1}and specific energy of 41 · 6 Wh.kg^{? 1}with 95% coulombic efficiency.     

Behavior of alkali element uranosilicates and uranogermanates in saturated aqueous solutions

The behavior of uranosilicates and uranogermanates of the series A^IHB^IVUO₆·nH₂O (A^I = Li, Na, K, Rb, Cs, NH₄; B^IV = Si, Ge) in aqueous solutions at pH from 0 to 14 was studied. The acid-base intervals of the existence of these compounds were determined, their conversion products were identified, and the solubility of A^IHB^IVUO₆·nH₂O was measured. The physicochemical analysis of the heterogeneous systems A^IHB^IVUO₆·nH₂O-aqueous solution was performed. The equilibrium constants of the dissolution reactions and the Gibbs functions of formation of A^IHB^IVUO₆·nH₂O were calculated. The solubility curves and the speciation diagrams of U(VI) and element B^IV in aqueous solutions and of the equilibrium solid phases were constructed.     

Lattice and grain boundary diffusion of copper in thin aluminum films

The lattice D₁ and grain boundary δD_b diffusivities of Cu in Al thin films at 130–185°C are calculated from measurements employing Auger electron spectroscopy and Ar ion beam etching. The calculated values are D₁ = 0.065 cm² s^-1 × exp(-122 kJ/RT) and δD_b = 4.5 × 10^-9 cm³s^-1 exp(-97.4 kJ/RT). The D₁ value is 3–5 times larger at 130–185°C than that predicted by an extrapolation of radioactive tracer measurements of large grain bulk specimens at 433–652°C. The higher value measured here is attributed to the higher density of subgrain defect structures in the thin film.     

Crystallization of salts M3[NpO4(OH)2]·nH2O (M = Na, K, Rb, Cs) from concentrated alkali solutions at low temperatures. Synthesis and structure of a new Np(VII) compound, Na3[NpO4(OH)2]·6H2O

Precipitation of salts M₃[NpO₄(OH)₂]·nH₂O (M = Na, K, Rb, Cs) from concentrated alkali solutions at low temperatures (about ?10°C) was studied. From solutions with [OH^?] > 9.5 M, these compounds are isolated as coarse black crystals in high yield without impurity of other phases. The K, Rb, and Cs salts crystallize in the form of the previously studied compounds K₃[NpO₄(OH)₂]·2H₂O and M₃[NpO₄(OH)₂]·3H₂O (M = Rb, Cs). In the case of Na, a new hydrate Na₃[NpO₄(OH)₂]·6H₂O was obtained, and its crystal structure was determined. Crystals of the hexahydrate consist of centrosymmetrical tetragonal-bipyramidal anions [NpO₄(OH)₂]^3?, crystallographically independent Na(1) and Na(2) cations, and water molecules. The coordination surrounding of the Np atom is characterized by noticeable difference (Δ = 0.0203 Å) in the Np-O bond lengths in the equatorial plane of the bipyramid. The [NpO₄(OH)₂]^3? anions are combined with the Na(2) cations to form infinite chains [Na(2)NpO₄(OH)₂(H₂O)₂]^2? in such a manner that the lateral edges of the anion are simultaneously the lateral edges of the Na(2) coordination polyhedron. Incorporation of one of the two crystallographically independent O atoms of the NpO₄ group into the Na(2) coordination surrounding is responsible for a noticeable difference in the Np-O bond lengths in the equator of the [NpO₄(OH)₂]^3? anion. The types of hydrogen bonding in the structures of Na3[NpO₄(OH)₂]·nH₂O (n = 0, 2, 4, 6) are compared.     

A single crystal X-ray diffraction study of Na4(UO2)4(i-C4H9COO)11(NO3)·3H2O

Synthesis and the results of IR and single crystal X-ray diffraction study of Na₄(UO₂)₄(i-C₄H₉COO)₁₁·(NO₃)·3H₂O are reported. The crystals are monoclinic; the unit cell parameters at 100 K are as follows: a = 13.697(2), b = 20.285(3), c = 15.991(3) Å, β = 103.760(3)°, space group P2₁, Z = 2, R = 0.0650. The uraniumcontaining structural units are mononuclear moieties [UO₂(i-C₄H₉COO)₃]^? and [UO₂(NO₃)(i-C₄H₉COO)₂]^?, belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = i-C₄H₉COO^? and NO ₃ ^? ) of uranyl complexes. The IR data are consistent with the results of the single crystal X-ray diffraction study. The influence of the carboxylate ligand volume on the structure of Na[UO₂L₃]·nH₂O crystals (L = acetate, n-butyrate, isovalerate ion) is analyzed.     

The kinetics of the thermal devitrification of the TiNi-TiCu amorphous alloy

Investigation of the devitrification process of the amorphous alloy of the composition 50 Ti, 45 Cu and 5 at% Ni was performed by differential scanning calorimetry (DSC). It was shown that devitrification occurs in two steps. The first step corresponds to the process of thermal relaxation of the amorphous state without crystallization at 674.5 K (β = 20 K/min.). The second step presents real crystallization at 741.7 K (β = 20 K/min.) during which polycrystallites of intermetallic phases TiCu and TiNi are formed. The kinetic and thermal parameters of both steps of devitrification were determined. The activation energy is E₁ = 446.93 kJ/mol for the first, and E₂ = 288.74 kj/mol for the second step; the frequency factor for the first step is Z₁ = 1.66 × 10⁻³⁵ min.⁻¹ and Z₂ = 2.72 × 10⁻²⁰ min.⁻¹ for the second one. The enthalpy of the first step is ΔH₁ = −17 J/g of the second ΔH₂ = −469 J/g. The dependence of the crystallization rate constant on temperature was also shown.     

YBa2SnO5·5, a novel ceramic substrate for YBCO and BiSCCO superconductors

YBa₂SnO_5·5 has been synthesized and sintered as single phase material for its use as substrate for both YBCO and BiSCCO superconductors. YBa₂SnO_5·5 has a complex cubic perovskite (A₂BB’O₆) structure with the lattice constanta = 8·430 Å. The dielectric constant and loss factor of YBa₂SnO_5·5 are in a range suitable for its use as substrate for microwave applications. YBa₂SnO_5·5 is found to be chemically compatible with both YBCO and BiSCCO superconductors. The thick film of YBCO screen printed on polycrystalline YBa₂SnO_5·5 substrate gave aT _c(0) of 92 K and a critical current density (J _c) of 4 × 10⁴ A/cm² at 77 K. A screen printed BiSCCO thick film on YBa₂SnO_5·5 substrate gaveT _c(0) = 110 K and current density 3 × 10³ A/cm² at 77 K.     

Stress relaxation following heating of nanocrystalline nickel

Stress relaxation of nanocrystalline nickel within the range of temperatures from 523 to 673K (0.17–0.27·T_m) in the regime of uniaxial compression is studied. The results obtained for nickel with more coarse grains are given for comparison. An average strain rate of nanocrystalline nickel within the investigated range of temperatures is 1.75·10⁻⁵–3.03· 10⁻⁵s⁻¹. The presence of two types of stress relaxation dependencies is shown. The most probable mechanism of plastic strain is grain boundary sliding controlled by grain boundary diffusion for 623–673K. At lower test temperatures, 523–573K, a plastic strain occurs by the powder law creep according to the Weertman model.     

Studies of compound formation at CuIn,AgIn and AuIn interfaces with perturbed γ-γ angular correlations

The thermal behaviour of the thin metal film couples Cu/In, Ag/In and Au/In was studied using the perturbed γ-γ angular correlation method. Formation of interface compounds CuIn₂, AgIn₂ and AuIn₂ was observed above temperatures T of 240 K, 220 K and 260 K respectively. The CuIn₂ and AgIn₂ compounds start to decompose above temperatures of 440 K and 460 K, though for AuIn₂ no decomposition was observed up to 550 K. The interface compounds are characterized by the following electric field gradient parameters (atT = 77 K): CuIn₂V_zz = 4.3(7) × 10¹⁷ V cm ⁻²η = 0.57(1) AgIn₂V_zz = 3.7(6) × 10¹⁷ V cm ⁻²η = 0.16(2) AuIn₂V_zz = 0η = 0Isothermal annealing of the film couples yielded a square root of time behaviour for the average interface compound thickness, which supports the assumption of a diffusion-controlled growth mechanism. Diffusion constants D₀ and activation energies E_a were evaluated from an Arrhenius plot as follows: CuIn₂D₀ = 1.0(3) × 10⁻⁶cm²S⁻¹E_a = 0.42(2) eV AgIn₂D₀ = 4(3) × 10⁻⁵cm²S⁻¹E_a = 0.46(3) eV AuIn₂D₀ = 2(1) × 10⁻⁹cm²S⁻¹E_a = 0.31(4) eV     

Formation of excited uranyl ion in oxidation of U(IV) with xenon difluoride in aqueous solutions of sulfuric and deuterated sulfuric acids

Kinetic features of the chemiluminescence accompanying oxidation of U(IV) with xenon difluoride in solutions of 0.2 M H₂SO₄ in H₂O and 0.2 M of D₂SO₄ in D₂O at temperatures within 283–313 K and concentrations (M) 10^?6 ≤ [U(IV)] ≤ 10^?4 and 10^?4 ≤ [XeF₂] ≤ 10^?3 were examined. The shape of the kinetic curve depends on the concentration of the reactants and the solution temperature. At [U(IV)] = 10^?6 and [XeF₂] = 10^?4 M, the curve exhibits a maximum, more prominent at low temperatures. At relatively high concentration ([U(IV)] = 10^?4 and [XeF₂] = 10^?3 M), self-acceleration of the reaction is observed: The mechanism of oxidation of U(IV) turns into a branched-chain mode owing to a higher concentration in the solution of radicals ^·OH, HO ₂ ^· , and XeF ₂ ^· , whose additional amounts are yielded by hydrolytic reduction of XeF₂. A kinetic isotope effect of the solvent k _H/k _D was revealed, which attains a maximum of 1.8 at 283 K. The activation energies of the oxidation of U(IV) with xenon difluoride in H₂SO₄ and D₂SO₄ solutions were estimated at E _a,H = 12 and E _a,D = 13 kcal mol^?1, respectively. The occurrence of the isotope effect is an indirect evidence of participation in the reaction of the OH (or OD) groups. The rate of hydrolytic reduction of XeF₂ in deuterated solvent (0.2 M D₂SO₄ in D₂O) in its photochemical stage is several times lower, and the luminescence accompanying the reaction is by an order of magnitude smaller than that in 0.2 M H₂SO₄.     

On the Evaporation of C60 in Vacuum and Inert Gases at Temperatures Between 830 K and 1050 K

Abstract

The binary diffusion coefficient D_AB of subliming C₆₀ in He, N₂ and Ar gas has been determined at a gas pressure between 5 and 10 kPa. It resulted D_AB/(cm^2/s)=D_o(P_o/P_t(T/T_o)ⁿ as a function of the total pressure P_t of the vapor phase and temperature T. At T_o=273 K and P_o=1.0133×10⁵ P_a, the values D_o = (0.059±0.004) cm²/s, (0.011±0.003) cm²/s, (0.012±0.007) cm²/s, n = 1.77±0.06, 2.02±0.18, 1.77±0.37 were obtained for He, N₂, Ar and (830-1000) K, (800-1020) K, (875-1095) K, respectively. Only 40 wt% of the initial C₆₀ material yielded reliable D_AB where the vapor pressure of C₆₀ followed log₁₀(P/Pa) = -(8976±60)/T/K+(11.05±0.07) for T between 640 and 1055 K.     

Effect of solvent ratio on the properties of highly oriented sprayed fluorine-doped tin oxide thin films

Transparent conducting thin films of F:SnO₂ have been deposited onto preheated glass substrates by a spray pyrolysis technique using pentahydrate stannic chloride (SnCl₄·5H₂O) and ammonium fluoride (NH₄F) as precursors and mixture of water and propane-2-ol as solvent. The concentration of SnCl₄·5H₂O and NH₄F is kept fixed and the ratio of water and propane-2-ol solvent in the spraying solution is varied. A fine spray of the source solution using air as a carrier gas has grown films of thickness up to 995 nm. Optical absorption, X-ray diffraction, Van der Pauw technique for measurement of a sheet resistance and Hall effect measurements at room temperature for determination of carrier density and conductivity have been used. The as-deposited films are of polycrystalline SnO₂ with a tetragonal crystal structure and are preferentially having orientation along the (200) direction with texture coefficient as high as 6.16. The average grain size for the as-deposited sample is found to be of the order of 44 nm. The films have moderate optical transmission (up to 70–85% at 550 nm). The figure of merit (ϕ) values vary from 1.95 · 10^− 3 to 35.68 · 10^− 3 Ω^− 1. The films are heavily doped, degenerate and exhibit n-type electrical conductivity. The lowest sheet resistance (R_s) for the optimized sample is 5.1 Ω. The films have a resistivity of 5.43 · 10^− 4 Ω cm and mobility around 7.38 cm² V^− 1 s^− 1.     

Identification of thaumasite in concrete by Raman chemical imaging

Identification of thaumasite (CaSiO₃·CaO₃·CaSO₄·15H₂O) in concrete undergoing external sulfate attack by X-ray powder diffraction or by microscopic techniques is difficult due to its crystallographic and morphological similarity with ettringite. Widefield Raman chemical imaging via liquid crystal tunable filter (LCTF) technology has been used in a preliminary study to determine the presence of thaumasite in association with ettringite (3CaO·Al₂O₃·3CaSO₄·32H₂O) and gypsum (CaSO₄·2H₂O). Raman chemical imaging combines Raman spectroscopy with optical microscopy and digital imaging to provide images with molecular-based contrast. Thaumasite has three major peaks at 658, 990, 1076 cm⁻¹ and three minor peaks at 417, 453, 479 cm⁻¹. Ettringite has major peaks at 990, 1088 cm⁻¹. Gypsum has a major peak at 1009 cm⁻¹ and minor peaks at 417, 496, 621, 673, 1137 cm⁻¹. When these minerals are presented together, Raman chemical imaging provides an excellent way to determine their molecular composition and spatial distribution within the sample.     

Molecular beam epitaxial growth of high-quality InP layers from solid phosphorus using a valved phosphorus cracker cell

We report the molecular beam epitaxial (MBE) growth of epitaxial InP using a valved phosphorus cracker cell at a range of cracking-zone temperatures (T_cr = 875–950°C), V/III flux ratios (V/III = 1.2–9.3) and substrate temperatures (T_s = 360–500°C). The as-grown epitaxial InP on an InP (100) substrate is found to be n-type from Hall measurements. The background electron concentration and mobility exhibit a pronounced dependence on the cracking-zone temperature, V/III flux ratio and substrate temperature. Using a T_cr of 850°C, the highest 77 K electron mobility of 40 900 cm² (V s)⁻¹ is achieved at a V/III ratio of 2.3 and a T_s of 440°C. The correponding background electron concentration is 1.74 × 10¹⁵ cm⁻³. The photoluminescence (PL) spectra show two prominent peaks at 1.384 and 1.415 eV, with the intensity of the low-energy peak becoming stronger at higher cracking-zone temperatures. The lowest PL FWHM achieved at 5 K is 5.2 meV. Within the range of substrate temperatures investigated, the effect on the crystalline quality determined from X-ray diffraction (XRD) measurements is not significant.     

Superplasticity of a Zn-1.1 WT.% Al alloy at high temperatures

The Zn-1.1 wt.% Al alloy exhibits superplastic properties in the temperature range from 292 K (0.42 Tm) to 635 K (0.92 Tm). The best properties were observed at the temperature of 520 K (0.75 Tm). The parameter m reaches the value m = 0.73 at the true strain-rate ϵ = 7 × 10⁻⁵s⁻¹, and the maximum ductility is A = 1020% at the initial strain-rate ϵ₀ = 1.7 × 10⁻⁴s⁻¹. This value is the highest one observed in low-alloyed ZnAl alloys and shows that materials with great volume fraction of the second phase with very good superplastic properties can be reached at comparably high homologous temperatures also in low-alloyed materials. The extreme values of m and A were observed in the material with the initial mean grain size d = 17 um.     

Metal-Free Hexagonal Perovskite High-Energetic Materials with NH3OH+/NH2NH3+ as B-Site Cations

Designing and synthesizing more advanced high-energetic materials for practical use via a simple synthetic route are two of the most important issues for the development of energetic materials. Through an elaborate design and rationally selected molecular components, two new metal-free hexagonal perovskite compounds, which are named as DAP-6 and DAP-7 with a general formula of (H₂dabco)B(ClO₄)₃ (H₂dabco²⁺ = 1,4-diazabicyclo[2.2.2]octane-1,4-diium), were fabricated via an easily scaled-up synthetic route using NH₃OH⁺ and NH₂NH₃⁺ as B-site cations, respectively. Compared with their NH₄⁺ analog ((H₂dabco)(NH₄)(ClO₄)₃; DAP-4), which has a cubic perovskite structure, DAP-6 and DAP-7 have higher crystal densities and enthalpies of formation, thus exhibiting higher calculated detonation performances. Specifically, DAP-7 has an ultrahigh thermal stability (decomposition temperatures (T_d) = 375.3 °C), a high detonation velocity (D = 8.883 km·s⁻¹), and a high detonation pressure (P = 35.8 GPa); therefore, it exhibits potential as a heat-resistant explosive. Similarly, DAP-6 has a high thermal stability (T_d = 245.9 °C) and excellent detonation performance (D = 9.123 km·s⁻¹, P = 38.1 GPa). Nevertheless, it also possesses a remarkably high detonation heat (Q = 6.35 kJ·g⁻¹) and specific impulse (I_sp = 265.3 s), which is superior to that of hexanitrohexaazaisowurtzitane (CL-20; Q = 6.23 kJ·g⁻¹, I_sp = 264.8 s). Thus, DAP-6 can serve as a promising high-performance energetic material for practical use.     

Oxygen-deficient ammonium vanadate for flexible aqueous zinc batteries with high energy density and rate capability at −30 °C

Aqueous zinc batteries (AZBs) have received significant attention owing to environmental friendliness, high energy density and inherent safety. However, lack of high-performance cathodes has become the main bottleneck of AZBs development. Here, oxygen-deficient NH₄V₄O_10−x·nH₂O (NVOH) microspheres are synthesized and used as cathodes for AZBs. The experimental test and theoretical calculations demonstrate that the oxygen vacancies in the lattice lower the Zn²⁺ diffusion energy barrier, which enables fast Zn²⁺ diffusion and good electrochemical performance in a wide temperature range. The suppressed side reactions also can help to improve the low temperature performance. NVOH shows a high energy density of 372.4 Wh kg⁻¹ and 296 Wh kg⁻¹ at room temperature and −30 °C, respectively. Moreover, NVOH maintains a 100% capacity retention after 100 cycles at 0.1 A g⁻¹ and ∼94% capacity retention after 2600 cycles at 2 A g⁻¹ and −30 °C. Investigation into the mechanism of the process reveals that the capacity contribution of surface capacitive behaviors is dominant and capacity attenuation is mainly caused by the decay of diffusion-controlled capacity. Furthermore, flexible AZBs can steadily power portable electronics under different bending states, demonstrating its great potential in wide-temperature wearable device.     

Preparation and characterization of the magnesium aluminophosphate MAPO-39

MAPO-39, a small-pore magnesium aluminophosphate molecular sieve (ATN topology), has a pore opening of 4.0 Å and tetragonal symmetry. The preparation of MAPO-39 was studied using a one-gel composition and different crystallization periods. Pure MAPO-39 was obtained by hydrothermal crystallization of the gel (molar composition: 1.1 n-Pr₂NH · 0.40 MgO · 0.80 Al₂O₃ · 1.02 P₂O₅ · 41 H₂O) at 423 K for 96 h. Investigations on the crystal structure, morphology, thermal conversion, and surface properties of the crystalline product were carried out. The crystallinity of MAPO-39 increases with increase in the crystallization period up to 96 h and decreases beyond the period of 96 h. As compared with MAPO-43 (another 8-O ring molecular sieve), MAPO-39 could be calcined at a higher temperature (up to 793 K) without any loss of the crystal structure. MAPO-39 possesses H₂O-sorption capacity of 0.226 cm³ g⁻¹. SEM investigations reveal that the crystals of MAPO-39 are irregular platelike in shape and 2.5 × 3.5 μm in size, X.p.s. analysis indicates that the concentration of aluminum is significantly higher on the surface than in the bulk and the observed binding energy of Mg_2p (50.3 eV) corresponds to that of tetrahedrally coordinated magnesium.     

Water-Stabilized Vanadyl Phosphate Monohydrate Ultrathin Nanosheets toward High Voltage Al-Ion Batteries

Al ion batteries (AIBs) are attracting considerable attention owing to high volumetric capacity, low cost, and high safety. However, the strong electrostatic interaction between Al³⁺ and host lattice leads to discontented cycling life and inferior rate capability. Herein, a new strategy of employing water molecules contained VOPO₄·H₂O to boost Al³⁺ migration via the charge shielding effect of water is reported. It is revealed that VOPO₄·H₂O with water lubrication effect and smaller steric hindrance owns high capacity and fast Al³⁺ diffusion, while the loss of unstable water upon cycling leads to a rapid performance degradation. To address this problem, ultrathin VOPO₄·H₂O@MXene nanosheets are fabricated via the formed Ti O V bond between VOPO₄·H₂O and MXene. The MXene aided exfoliation results in enhanced V O_water bond strength between H₂O and VOPO₄ that endows the obtained composite with strong water holding ability, contributing to the extraordinary cycling stability. Consequently, the VOPO₄·H₂O@MXene delivers a high discharge potential of 1.8 V and maintains discharge capacities of 410 and 374.8 mAh g⁻¹ after 420 and 2000 cycles at the current densities of 0.5 and 1.0 A g⁻¹, respectively. This work provides a new understanding of water-contained AIBs cathodes and vital guidance for developing high-performance AIBs.