Improved Li- storage performance of heat-treated InFeCoO<Subscript>4</Subscript> spinel prepared by glycine assisted chemical route

Herein, we show the synthesis of high-capacity anode, InFeCoO₄ spinel for lithium ion batteries (LIBs), by facile glycine-assisted chemical approach. The structure and morphology are evaluated by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and scanning electron microscopy (SEM) techniques, respectively. The pure phase formation of spinel InFeCoO₄ is confirmed from XRD pattern, whereas the oxidation state of Co in 2+ is determined from XAS analysis. Electrochemical performance of InFeCoO₄ in the half-cell configuration is evaluated by galvanostatic and cyclic voltammetry (CV) in the voltage window of 0.005–3.0 V vs. Li. When cycled at 60 mA g^?1, it shows a high first cycle reversible capacity of 750 (±10) mA h g^?1. However, slow capacity degradation is noticed upon cycling and reached 285 (±10) mA h g^?1 after 40 cycles. An improved Li-storage performance is noticed under similar cycling condition, when the electrode is heat-treated. It shows first cycle reversible capacity of 880 (±10) mA h g^?1 and reached 535 (±10) mA h g^?1 after 40 cycles. The coulombic efficiency is >98 % during cycling. The improved Li-storage performance is possibly due to the distribution of PVDF (binder) in the active materials as well as better electrical contact after heat treatment.     

EPR and Optical Absorption Study of VO2+-Doped Lithium Hydroxylammonium Sulphate

ABSTRACT

Single-crystal and powder EPR studies of VO²⁺-doped lithium hydroxylammonium sulphate (LiNH₃OHSO₄) were carried out at room temperature. The results indicate the presence of two magnetically inequivalent VO²⁺ sites. The VO²⁺ ion takes up a substitutional position in the host lattice. The angular variation of EPR spectra in three mutually perpendicular planes were used to determine the spin Hamiltonian parameters, and the values obtained were the following: For Site 1, g_x = 2.0249 ± 0.0002, g_y = 1.9698 ± 0.0002, g_z = 1.9552 ± 0.0002, A_x = (51 ± 2) × 10^?4 cm^?1, A_y = (93 ± 2) × 10^?4 cm^?1, and A_z = (165 ± 2) × 10^?4 cm^?1; and for Site 2, g_x = 2.0267 ± 0.0002, g_y = 1.9743 ± 0.0002, g_z = 1.9213 ± 0.0002, A_x = (40 ± 2) × 10^?4 cm^?1, A_y = (80 ± 2) × 10^?4 cm^?1, and A_z = (155 ± 2) × 10^?4 cm^?1. The optical absorption spectrum recorded at room temperature shows four bands. From the optical and EPR data, various molecular coefficients are evaluated, and the nature of bonding in the crystal is discussed.     

Isotopic characteristics of meteoric waters in the Belgrade region

Abstract

The stable isotope composition of hydrogen (δ²H) and oxygen (δ¹⁸O) in monthly precipitation and river water (Sava River and Danube) samples in the Belgrade area gathered between 1992 and 2005 are determined. The local meteoric water line δ²H=7.8 (±0.2) δ¹⁸O+7.3(±1.6) (r ²=0.98, n=60, σ=0.52) for the whole period of observation is close to the global meteoric water line. The amount-weighted mean δ²H and δ¹⁸O values of precipitation were?65±27 ‰ and?9.4±3.4 ‰, respectively. Good correlation between δ¹⁸O values (r>rsim0.67) and ambient temperature and relative humidity was obtained. Stream-water data ranged from?94 to?60 ‰ for δ²H and from?11.0 to ～5.7 ‰ for δ¹⁸O with highly statistically significant difference (p>0.01) between the Sava River and the Danube. In addition, the isotopic compositions of local precipitation and adjacent river water at monitoring sites were compared. Obtained data will give an opportunity to improve the knowledge of mixing stream water and local groundwater, and assessment of potential groundwater risks and pressures in the Belgrade basin.     

N2O emissions and source processes in snow-covered soils in the Swiss Alps

Nitrous oxide (N₂O) emissions from snow-covered soils represent a significant fraction of the annual flux from alpine, subalpine or cold-temperate regions. In winter 2010–2011, we investigated the temporal variability of N₂O emissions and source processes from a subalpine valley in the Swiss Alps. The study included regular measurements of N₂O snow profiles at a fixed location and an intensive sampling campaign along a transversal cut through the valley with grassland at the bottom and coniferous forest at the slopes. During the intensive campaign, recently developed laser spectroscopy was employed for high-precision N₂O isotopomer analysis. Maximum N₂O fluxes (0.77±0.64 nmol m^?2 h^?1) were found for periods with elevated air temperature and, in contrast to our expectations, were higher from forest than from grassland in mid-February. At maximum snow height (63 cm) the main N₂O source processes were heterotrophic denitrification and nitrifier denitrification. The reduction of N₂O by heterotrophic denitrifiers was much more pronounced for the grassland compared with the forest soil, as indicated by the ¹⁵N site preferences of 16.4±11.5 ‰ (grassland) and?1.6±2.1 ‰ (forest). This illustrates the potential of laser spectroscopic N₂O isotopomer analysis for the identification of source processes even at low emission rates in nutrient poor ecosystems.     

Electromagnetic transition strengths in 24Na

Mean lifetimes, excitation energies and branching ratios of ²⁴Na states, populated in the ²³Na(d, p)²⁴Na reaction have been measured. Gamma-ray spectra were measured at three angles in coincidence with proton groups at θ_p = 169°. Mean lifetimes obtained from DSA are (excitation energy in keV, lifetime in fs): 563, > 1000; 1341, 95 ± 30; 1344, 38 ± 11; 1346, > 1500; 1512, 38 ± 11; 1846, 260 ± 50; 1885, 36 ± 9; 2513, 15 ± 7; 2563, < 25; 2904, 50 ± 15; 2978, < 25; 3216, 22 ± 8; 3372, 19 ± 5. For higher levels up to 4207 keV upper limits of 30 fs were set. In combination with earlier work the following unique spin(-parity) assignments could be made: J^π(1846) = 2⁺, J(2513) = 3, J^π(3745) = 3^?. A new level at E_x = 3681.7 ± 0.6 keV is reported.     

EPR of Cu2+ Impurities in Cytosine Hydrochloride: A Case of Superhyperfine Structure

Electron paramagnetic resonance spectra of Cu²⁺ impurities in cytosine hydrochloride single crystals are observed at liquid nitrogen temperature. Two magnetically equivalent sites for Cu²⁺ have been observed. The parameters of ⁶³Cu obtained with the fitting of spectra to rhombic symmetry spin Hamiltonian are: g _x  = 2.047 ± 0.002, g _y  = 2.187 ± 0.002, g _z  = 2.390 ± 0.002, A _x  = (86 ± 3) × 10^?4 cm^?1, A _y  = (87 ± 3) × 10^?4 cm^?1, and A _z  = (138 ± 3) × 10^?4 cm^?1. The observed bands in optical spectra of the single crystal recorded at room temperature are assigned to various d–d and charge-transfer transitions. Using both EPR and optical data, the nature of bonding of metal ion with different ligands is discussed.     

Chirp control of femtosecond laser-filamentation-induced snow formation in a cloud chamber

Filamentation-induced water condensation and snow formation are investigated using laser pulses with different chirps and pulse widths. Chirped pulses result in the laser filamentation with different spatial lengths and intensities, which has a great impact on airflow motion and snow formation. The experiments show that snow formation mainly relates to the filament intensity distribution. Negative chirped pulses produce a greater amount of snow because of higher intensity inside the filaments as compared with the positive chirped pulses.     

On injection of hydrate-forming gas into a gas-saturated snowy agglomerate while transition through the ice melting point

The paper considers the process of injection of hydrate-forming gas (methane) into a snowy agglomerate (ini-tially saturated with methane). The self-similar problem statement demonstrates that if the warm gas (T_e > 0 °C) is injected under a high pressure (p_e ≥ p_*, where the critical values are found from the initial temperature T₀, pressure p₀, volumetric snow saturation S_i0, and permeability of snow) into the filtration zone with phase transition, this produces four characteristic zones: the nearest zone with all snow transformed into hydrate, therefore, the aggregate filled only with gas and hydrate, the two intermediate zones where gas, snow or water and hydrate are in phase equilibrium state, and the distant zone filled only with gas and snow. The obtained analytical and numerical solutions give an analysis of the influence of key input parameters like initial state of the aggregate, gas injection rate, and its temperature, on the structure and the length of four filtration zones.     

Study on ammonium acetate salt-added polyvinyl alcohol-based solid proton-conducting polymer electrolytes

Polyvinyl alcohol (PVA) complexes with different compositions of ammonium acetate (AA) are prepared by solution cast technique. Polyvinyl alcohol crystallinity decreased with increasing ammonium acetate salt content. Molecular weight and density of polyvinyl alcohol complex increased with the addition of ammonium acetate salt. The ammonium acetate salt addition resulted in plasticization and hence decreased glass transition temperature (T _g) as well as hardness number (HV). 80PVA:20AA presented maximum conductivity (σ?=?1.3?×?10^?7S cm^?1 at 303 K) with minimum activation energy (E _a) 0.151 eV below the T _g. The proton transport number determined using EMF method found ≈0.98 for polymer complex with ammonium acetate content >15 mol%. The complex impedance is measured as a function of frequency, temperature, relative humidity, and hydrogen partial pressure. Enhanced bulk conductivity with increased H₂ partial pressure and relative humidity suggested H⁺ mobility within complex polymer electrolyte.     

Unusual EPR Spectra with Inverse Axial g values of Chlorosalicylate–Cu(II)–2,6-Pyridinedimethanol Complex in Frozen Water–Methanol Solution

Copper(II) complex systems containing 3,5-di, 4-, or 5-chlorosalicylic acids (X-ClsalH) and different copper(II) salts (copper acetate (Cu(ac)₂) or copper sulphate (CuSO₄)), with varying 2,6-pyridinedimethanol (pydime) concentration, [Cu(ac)₂(aq) or CuSO₄(aq) + 2 (X-ClsalH(solv)) + x pydime(solv)], where X = 3,5-di, 4-, or 5- and x = 0, 1, 2, 4, or 8, were prepared. The effects of two copper(II) salts (containing anions of different basicity) and N-donor ligand (pydime) with varying ligand-to-metal ratio (x) on the formation of resulting complexes were studied by electron paramagnetic resonance (EPR) spectroscopy in frozen water/methanol (1:3 v/v) solutions. For x ≥ 2, unusual Cu(II) EPR spectra with "inverse" axial g values of (g _⊥ > g _∥ > 2.0023) were observed, which can indicate the compressed octahedral geometry of the central copper atom with the unpaired electron/hole localized on the $ d_{{z^{2} }} $ orbital. However, for x = 1, composite Cu(II) EPR spectra with both "usual" and "inverse" axial g values were detected. Finally, for x = 0 (ligand not present) Cu(II) EPR spectra only with the ‘usual’ axial g values of g _∥ > g _⊥ > 2.0023 were collected, which can indicate the elongated octahedral geometry of the central copper atom with the unpaired electron/hole localized on $ d_{{x^{2} - y^{2} }} $ orbital. The above described observations are independent of the usage of different copper(II) salts and X-chlorosalicylic acids.     

Removal of low-concentration benzene in indoor air with plasma-MnO2 catalysis system

Non-thermal plasma (NTP) and combined plasma-MnO₂ catalytic (CPMC) air cleaners were tested for removal of low-concentration benzene in air. Both air cleaners were made of stainless steel needle matrix plate and used DC corona discharger. The effects of discharge power and relative humidity (RH) on benzene removal efficiency were investigated in a closed chamber. The intermediate products produced in purification processes were analyzed using gas chromatography-mass spectrometer (GC-MS). The concentrations of discharge byproducts and CO₂ selectivity produced in both processes were also compared. It was found that the benzene removal efficiency increased with discharge power in both systems; With the increase of RH in air, benzene removal efficiency firstly increased and then decreased in NTP while it gradually decreased in CPMC. For a fixed discharge power of 9 W and RH of 20% in CPMC, the conversion of benzene increased from 82.9% to 89.6%, the CO₂ selectivity increased from 38% to 80%, the concentration of O₃ decreased from 25.3 ppm to 1.3 ppm, and NO₂ formation decreased from 234 ppm to 25.7 ppm, compared with NTP.     

Toxicity of zinc oxide nanoparticles to zebrafish embryo: a physicochemical study of toxicity mechanism

The biological impact of engineered nanomaterials released into the aquatic environment is a major concern. In this work, the properties of ZnO nanoparticles (nano-ZnO, 30 nm) were characterized in a water suspension (E3 medium), and a zebrafish 96-h post fertilization (hpf) embryo–larval test was performed to assess the toxicity of nano-ZnO suspension. Nano-ZnO was found to readily form aggregates with different sizes; small aggregates (142.4–517.7 nm) were still suspended in E3 medium, but large aggregates (>1 μm) quickly deposited on the bottom of 24-well plates; nano-ZnO was partially dissolved to Zn species (Zn_(dis)) in E3 medium. In the nano-ZnO suspension, small aggregates, Zn_(dis), and large aggregates might jointly exert influence on the development of zebrafish embryos. The embryo toxicity test revealed that nano-ZnO killed zebrafish embryos (50 and 100 mg/L), retarded the embryo hatching (1–25 mg/L), reduced the body length of larvae, and caused tail malformation after the 96 hpf exposure. Zn_(dis) only partially contributed to the toxicity of nano-ZnO. This research highlights the need to further investigate the ecotoxicity of nano-ZnO in the water environment.     

Modeling VHF emissivity of snow cover with account of its stratigraphy

In this paper, we discuss a model of emissivity of snow cover taking into account its structure. We assume that upward and downward radiation inside a snow layer are diffuse and apply the two-flux theory of Kubelka and Munk. Snow cover is modelled by a medium comprising discrete scatterers. In the case of dry snow, the scatterers are ice grains. Wet snow is modelled by a mixture of ice grains (with or without water envelopes) and water drops. We assume that the scatterers are spherical particles that have lognormal distribution over size. The brightness temperature of radio emission from snow cover on the soil is calculated using the data of glaciological measurements of physical parameters and microstructure of snow. Results of calculations are compared to measurements of the brightness temperature of radio emission from various types of snow covers. Space Research Institute of Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 9, pp. 845–857, August 1999.     

EPR, Optical Absorption and Superposition Model Study of Fe3+-Doped Ammonium Dihydrogen Phosphate Single Crystals

X-band electron paramagnetic resonance (EPR) studies are carried out on Fe³⁺ ions doped in ammonium dihydrogen phosphate (ADP) single crystals at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations. The obtained values of spin Hamiltonian and zero-field parameters of the Fe³⁺ ion in ADP are: g = 1.994 ± 0.002, |D| = (220 ± 5) × 10^?4 cm^?1 and a = (640 ± 5) × 10^?4 cm^?1. On the basis of EPR data, the site symmetry of the Fe³⁺ ion in the crystal is discussed. The Fe³⁺ ion enters the lattice substitutionally replacing the NH₄ ⁺ sites. The optical absorption of the crystal is also studied at room temperature in the wavelength range of 195–925 nm. The energy values of different orbital levels are calculated. The observed bands are assigned as transitions from the ⁶ A _1g (S) ground state to various excited quartet levels of the Fe³⁺ ion in a cubic crystalline field. From the observed band positions, Racah interelectronic repulsion parameters (B and C), cubic crystal field splitting parameter (D _q ) and Trees correction are calculated. There values are: B = 970, C = 1,923, D _q  = 1,380 cm^?1 and α = 90 cm^?1, respectively. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The zero-field splitting (ZFS) parameters are also determined theoretically using B _kq parameters estimated from the superposition model. The values of ZFS parameters thus obtained are |D| = (213 ± 5) × 10^?4 cm^?1 and |E| = (21 ± 5) × 10^?4 cm^?1.     

Role of ion energy flux on the structural and morphological properties of silicon oxy-nitride composite films deposited by plasma focus device

ABSTRACT

Crystalline silicon oxy-nitride (SiON) composite films are deposited on Si substrate for multiple (5, 15, 25 and 50) focus shots (FS) by plasma focus device. The X-rays diffraction patterns reveal the development of various diffraction peaks related to Si, Si₃N₄, and SiO₂ phases which confirms the formation of SiON composite film. The intensity of Si₃N₄ (1 0 2) plane is linearly increased with the increase of FS. The Si₃N₄ (1 0 2) phase does not nucleate for 5 FS. Raman analysis confirms the formation of β–Si–N phase. Raman and Fourier transform infrared spectroscopy analysis reveals that the strength of chemical bonds like Si–N, Si–O formed during the deposition process of SiON composite films is associated with the bonds intensity which in turn depends on the number of FS. The field emission scanning electron microscopic analysis reveals that the surface morphology like size, shape and distribution of micro/nano-dimensional particles, film compactness and the formation of micro-rods, micro-teethes and micro-tubes of SiON composite films is entirely associated with the rise in substrate surface transient temperature which in turn depends on the increasing number of FS. The EDX spectrum confirms the presence of Si (22.5?±?4.7 at. %), N (13.4?±?4.5 at. %) and O (54.7?±?11.3 at. %) in the SiON composite film. The thickness of SiON composite film deposited for 50 FS is found to ～15.47?µm.     

Transition metal doping of amorphous silica particles

Amorphous, homogeneously doped particles with 1–10 atomic percent (at%) nickel or zinc, smaller than 100 nm, were synthesized. Additionally, 20 at% nickel and zinc-doped silica particles were synthesized, although the particle size was > 300 nm. The coordination state of the metal in solution did not change with the ammonia or water concentrations used. Particle size was found to decrease with both increasing water and ammonia hydroxide concentrations. The NH₄OH concentrations of 4.5 and 6.5 M used allowed the formation of ammine–transition metal complexes and the zeta potential to remain in a stable range, allowing for spherical, nearly monodisperse particle formation at high metal dopant concentrations.     

Equation of state and thermal expansivity of LiF and NaF

The high-pressure and high-temperature behaviors of LiF and NaF have been studied up to 37 GPa and 1000 K. No phase transformations have been observed for LiF up to the maximum pressure reached. The B1 to B2 transition of NaF at room temperature was observed at ～28 GPa, this transition pressure decreases with temperature. Unit-cell volumes of LiF and NaF B1 phase measured at various pressures and temperatures were fitted using a P–V–T Birch–Murnaghan equation of state. For LiF, the determined parameters are: α₀ = 1.05 (3)×10^?4 K^?1, dK/dT = ?0.025 (2) GPa/K, V ₀ = 65.7 (1) Å³, K ₀ = 73 (2) GPa, and K′ = 3.9 (2). For NaF, α₀ = 1.34 (4)×10^?4 K^?1, dK/dT = ?0.020 (1) GPa/K, V ₀ = 100.2 (2) Å³, K ₀ = 46 (1) GPa, and K′ = 4.5 (1).     

Magnetic and electric studies of a new Co(II) perovskite-like material

Structural phase transitions in the perovskite-like material [(CH₄)₁₂(NH₃)₂]CoCl₄ have been observed using differential thermal scanning. The material shows an order-disorder transition at T ₁ = 396 ± 5 K with entropy, (ΔS ₁) = 12.8 J/mole/K. A "chain melting" transition with a major endothermic peak at T ₂ = 337 ± 3 K and a minor one at T ′ = 316 ± 2 K, has total entropy ΔS = 28 J/mole/K. At low temperatures, the transitions at T ₃ = 288 ± 3 K and at T ₄ = 188 ± 3 K, have entropies of ΔS ₃ = 14.4 J/mole/K and ΔS ₄ = 2.6 J/mole/K respectively. AC magnetic susceptibility in the temperature range 78-290 K, in a magnetic field of 160 A/m and at a frequency of 320 Hz is presented. The results indicate changes in symmetry at 188 K. Dielectric permittivity has been studied as a function of temperature in the range 300-430 K and frequency range (60 Hz-100 kHz), confirming the observed transitions. The dielectric permittivity reflects rotational and conformational transition for the material. The variation of the real part of the conductivity with temperature is thermally activated with different activation energies in the range of ionic hopping. The temperature dependence of the dc conductivity and that of the ions hopping rate have indicated that the concentration of mobile ions is independent of temperature. The dependence of the conductivity on frequency follows the universal power law, <artwork name="GPHT31040ei1"> in the temperature range 340 K<T<390 K. Values 0 <s ₁ <1 dominate at low frequency and correspond to translational hopping motion and values 1<s ₂<2 dominate at high frequencies and correspond to well localized hopping and/or reorientational motion. For T > 396 K, the AC conductivity was fitted to <artwork name="GPHT31040ei2"> with 0<s<1. Comparison with the corresponding Cu-containing material is discussed.     

Dielectric anomalous response of water at 60 °C

Recently, the paraelectric response of water was investigated in the range 0–100 °C. It showed an almost perfect Curie–Weiss behaviour up to 60 °C, but a slight change in slope of 1/ε_d versus T at 60 °C was overlooked. In this work, we report optical extinction measurements on metallic (gold and silver) nanoparticles dispersed in water, annealed at various temperatures in the range from 20 to 90 °C. An anomalous response at 60 °C is clearly detectable, which we associate to a subtle structural transformation in the water molecules at that temperature. This water anomaly is also manifested by means of a blue shift in the longitudinal surface plasmon resonance of the metallic nanoparticles for the solutions annealed at temperatures higher than about 60 °C. A reanalysis of 1/ε_d (T) for water in the whole temperature range leads us to conclude that the water molecule undergoes a subtle transformation from a low temperature (0–60 °C) configuration with a dipole moment μ₁ = 2.18 D (close to the molecular dipole moment of ice) to a high temperature (60–100 °C) configuration with μ₂ = 1.87 D (identical to the molecular dipole moment in water vapour).     

Crystallographic study of grain refinement in low and medium carbon steels

In order to clarify and articulate the long-standing problems associated with the role of various compounds in grain refinement of as-cast steels, a comprehensive crystallographic study on grain refiners in a number of low carbon steels has been conducted using the edge-to-edge matching (E2EM) model, which has been successfully applied to explain and predict effective grain refiners in light metals. Five commonly investigated compounds, namely NbO, CeS, TiN, Ce₂O₃ and TiC, in steels were examined. According to the extent of crystallographic matching, the predicted grain refining potency of these five grain refiners is ranked in the order of NbO > CeS > TiN > Ce₂O₃ > TiC, which is consistent with previously reported experimental results. Four different orientation relationships between δ-ferrite and these grain refiners were predicted. One of them has been verified by previously published experimental data. The similarity and the advantages of the E2EM model over conventional Bramfitt’s model were also discussed.