Liquid-Liquid Extraction, Separation, Preconcentration, and ICP-AES Determination of Lanthanum and Cerium with N-Phenyl-(1,2-methanofullerene C60)61-formohydroxamic Acid

A novel method for liquid-liquid extraction, separation, preconcentration, and simultaneous trace determination of cerium(IV) and lanthanum(III) with N-phenyl-(1,2-methanofullerene C₆₀)61-formohydroxamic acid (PMFFA) is reported. Lanthanum and cerium are extracted at pH 8.5 and 9.5, respectively in chloroform and recovered from monazite sands in the presence of thorium, uranium, and large number of cations and anions in high purity (99.98%). The extraction mechanism is investigated. The influence of PMFFA, pH, diverse ions, and temperature on the distribution constants of lanthanum and cerium was examined. The overall stability constants (log β₂K_e) and extraction constants (K_ex) for lanthanum(III) are 22.50 and 5.0 × 10^-9, respectively and for cerium(IV) are 21.51 and 3.9 × 10^-9, respectively. Lanthanum(III) gives a colourless complex with PMFFA which is extracted into chloroform having molar absorptivity 5.5 × 10⁴ L mol^-1 cm^-1 at 395 nm, and Beer's law 0.12-2.52 µg mL^-1, while cerium(IV) forms a red coloured complex, λ_max 460 nm, molar absorptivity 1.5 × 10⁴ L mol^-1 cm^-1, and Beer's law 0.46-9.26 µg mL^-1. For trace determination the extracts were directly inserted into the plasma for inductively coupled plasma atomic emission spectrometry ICP-AES measurements of lanthanum and cerium which increases the sensitivity 60 folds and obey Beer's law in the range, 2.1-37.5 ng mL^-1 for lanthanum and 9.2-186.4 ng mL^-1 for cerium. The method is applied for the determination of lanthanum and cerium in real and standard samples, sea water, and environmental samples.     

Effects of Annealing on the Conductivity of C60 Thin Films

Films of C₆₀, at different stages of annealing of T_t=200°and 300°C have been electrically characterized over the temperature domain from -130°C to T_t. X-ray diffraction revealed a random polycrystalline fee structure with stacking defects of an intrinsic nature, due to deposition conditions. The value of room-temperature conductivity was found to be in the range (6.3-1.0) *10^-10 (0cm)^-1. In the stable annealed state the conductivity showed an activated temperature dependence above 423 K and a non-activated dependence below 330-280 K. The activation energies E_a = 0.8 eV (film thickness 0.70 μm) and E_a = 1.0 eV (film thickness 2.40 μm) were in good agreement with the energy gap values (1.63 eV and 2.08 eV) which were deduced from the absorption spectral dependence. Annealing decreased the non-activated contribution to conduction, extending the intrinsic conduction temperature range.     

Dielectric Properties of (C60 + C70)—Ferroelectric Liquid Crystal Composite

A stable composite of fullerene and ferroelectric liquid crystal (FLC) has been obtained. Analysis of the frequency dependence of imaginary part of complex dielectric permittivity showed that orientation of the liquid crystal (LC) in the composite is close to homeotropic. At temperatures above 329 K, the composite conductance is determined by the conductance of fullerene. At 344 K, the composite conductance is 3.2 × 10^-8 Ω^-1 m^-1, and the activation energy for the temperature dependence of conductance is 0.99 eV. At temperatures below 329 K, the composite properties are determined by the LC, and the frequency dependences of the components of complex dielectric permittivity showed dispersion due to rotation of molecular dipoles around the helicoid (Goldstone mode) axis. The relaxation time is close to 1 msec and almost equal to the value obtained for homeotropically oriented LC.     

A Novel Fullerene Hydroxamic Acid for the Liquid-Liquid Extraction, Separation, Preconcentration, and Spectrophotometric and ICP-AES Determination of Vanadium

A new reagent N-phenyl-(1,2 methanofullerene C₆₀)61-formohydroxamic acid (PMFFA) is reported for extraction and trace determination of vanadium(V) in nutritional and biological substrates. The extraction mechanism of vanadium from 6 M HCl media is investigated. The influence of PMFFA, diverse ions, and temperature on the distribution constant of vanadium examined. The over all stability constant (log β₂K_e) and extraction constant (K_ex) are 20.89 ± 0.02 and 8.0 ± 0.02 × 10^-15, respectively in chloroform. The thermodynamics parameters are calculated and kinetics of vanadium transport is discussed. The system obeys Beer's law in the range of 3.2-64.0 ng mL^-1 of vanadium(V). The molar absorptivity is 7.96 × 10⁵ L mol^-1 cm^-1, at 510 nm. The PMFFA-vanadium(V) complex chloroform extract in chloroform was directly inserted into plasma for ICP-AES measurement, which increases the sensitivity by 50 folds and obey Beer's law in the range of 50-1200 pg mL^-1 of vanadium(V). The method is applied for determination vanadium in real standard samples, sea water, and environmental samples.     

Preparation, Electrical, and Dielectric Characterization of Crosslinked Polyvinyl Alcohol-Phosphotungstic Acid Nanocomposites

The work presents the electrical and dielectric characterization of proton-conducting, chemically-crosslinked nanocomposites of polyvinyl alcohol (PVA) and phosphotungstic acid (PTA). The composite membranes were prepared by in situ crosslinking of the polymer matrix in solution form, containing PTA. The electrical and dielectric properties of the membranes were investigated as a function of blending composition, crosslinking density, and temperature. The conductivity of these membranes shows a temperature dependence of Arrhenius type and highest conductivity of 3.31 × 10^-3 S cm^-1 was obtained. The activation energies for proton conduction were found to be in the range of 15.28-40.62 kJ mol^-1.     

Thermodynamic Properties and Hydrogen Accumulation Ability of Fullerene Hydride C60H36

Thermodynamic properties of fullerene hydride C₆₀H₃₆ in the ideal-gas and crystal states were studied by theoretical methods. Molecular structures and vibration frequencies were calculated for 9 isomers of C₆₀H₃₆ by the density functional theory (DFT) by use of a combination of the B3LYP functional with 6-31G* basis sets. Ideal-gas thermodynamic properties were calculated based on those parameters. Enthalpies of formation of C₆₀H₃₆ isomers in the ideal-gas state were derived from homodesmic reactions involving adamantane, cyclohexane, and C₆₀ fullerene. Using the standard methods of statistical mechanics, heat capacity and derived thermodynamic properties of crystalline C₆₀H₃₆ were calculated at 340-1000 K that extended the range of experimental measurements. With a crystal-gas heat capacity difference, the experimental value of sublimation enthalpy was extrapolated to room temperature as Δ_subH_m^o (298.15 K)=(193±10) kJ · mol^-1. Combining this value with the known experimental enthalpy of formation in the crystalline state, the ideal-gas enthalpy of formation of C₆₀H₃₆ at the synthesized sample isomer composition was obtained: Δ_f H_m^o (298.15 K)=(1206±28) kJ · mol^-1. Equilibrium constants and compositions were calculated for the reactions of hydrogenation of C₆₀ fullerene in different states. It was shown that C₆₀ can act as a hydrogen accumulator.     

Reaction Kinetics of C60 Fullerene Ozonation

It has been verified that the reaction between O₃ and C₆₀ follows the general second order reaction rate which is valid for all the reactions between ozone and unsaturated olefinic bonds: v = k[C=C][O₃]. The reaction rate constant k has been measured ≈(1.5 ± 0.3) × 10⁴ L mol^-1 s^-1. The value of this rate constant has the same order of magnitude of the rate constant measured for instance in the ozonation of 1,4-diphenylbutadiene.     

Spectroscopic Evidence for Anionic Coordination Complexes of the Transition Metals with C70 and the Higher Fullerenes C76, C78, C82, C84, C86, C90, and C92

The carbonylate anions [M(CO)₅]^- (M = Mn, Re), [Co(CO)₄]^-, [CpFe(CO)₂]^-, and [CpM(CO)₃]^- (M = Mo, W) react with C₇₀ via single electron transfer processes to give, respectively, the corresponding 17-electron, metal-centered radicals Co(CO)₄, M(CO)₅ (M = Mn, Re), CpFe(CO)₂, and CpM(CO)₃ (M = Mo, W) in addition to the radical anion C₇₀^-. In secondary thermal or photochemical processes, the metal-centered radicals Co(CO)₄ and M(CO)₅ (M = Mn, Re) combine with the C₇₀^- to form the new η²-C₇₀ complexes [Co(CO)₃(η²-C₇₀)]^- and [M(CO)₄(η²-C₇₀)]^-. However, the metal-centered radicals CpM(CO)₃ (M = Mo, W) require photolysis to react with C₇₀^- to form [CpM(CO)₂(η²-C₇₀)]^-, whereas neither thermolysis nor photolysis induces reaction between CpFe(CO)₂ and C₇₀^-. The photochemical reaction of [Mn(CO)₅]^- with a mixture of higher fullerenes known to contain at least C₇₆, C₇₈, C₈₄, C₈₆, and C₉₀ resulted similarly in the formation of the higher fullerene complexes [Mn(CO)₄(η²-C_n)]^- (n = 76, 78, 80, 82, 84, 86, 88, 90, 92, 96, and 98), all identified using electrospray mass spectrometry.     

Structure and electrical properties of (100)-oriented Pb(Zn1/3Nb2/3)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films on La0.7Sr0.3MnO3 electrode by chemical solution deposition

(100)-oriented 0.462Pb(Zn_1/3Nb_2/3)O₃–0.308Pb(Mg_1/3Nb_2/3)O₃–0.23PbTiO₃ (PZN-PMN-PT) perovskite ferroelectric thin films were prepared on La_0.7Sr_0.3MnO₃/LaAlO₃ (LSMO/LAO) substrate via a chemical solution deposition route. The perovskite LSMO electrode was found to effectively suppress the pyrochlore phase while promote the growth of the perovskite phase in the PZN-PMN-PT film. The film annealed at 700 °C exhibited a high dielectric constant of 2130 at 1 kHz, a remnant polarization, 2P_r, of 29.8 μC/cm², and a low leakage current density of 7.2 × 10^− 7 A/cm² at an applied field of 200 kV/cm. The ferroelectric polarization was fatigue-free at least up to 10¹⁰ cycles. Piezoelectric coefficient, d₃₃, of 48 pm/V was also demonstrated. The results showed that much superior properties could be achieved with the PZN-PMN-PT thin films on the solution derived LSMO electrode than on Pt electrode by sputtering.     

Transparent conducting F-doped SnO2 thin films grown by pulsed laser deposition

Transparent conducting fluorine-doped tin oxide (SnO₂:F) films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of the SnO₂:F films have been investigated as a function of F-doping level and substrate deposition temperature. The optimum target composition for high conductivity was found to be 10 wt.% SnF₂ + 90 wt.% SnO₂. Under optimized deposition conditions (T_s = 300 °C, and 7.33 Pa of O₂), electrical resistivity of 5 × 10^− 4 Ω-cm, sheet resistance of 12.5 Ω/□, average optical transmittance of 87% in the visible range, and optical band-gap of 4.25 eV were obtained for 400 nm thick SnO₂:F films. Atomic force microscopy measurements for these SnO₂:F films indicated that their root-mean-square surface roughness ( 6 Å) was superior to that of commercially available chemical vapor deposited SnO₂:F films ( 85 Å).     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.     

Ozone Reaction with C70 and C60 Fullerenes: The Effect of Temperature on the Reaction Kinetics

It has been confirmed that the effect of temperature on the rate constants (k) of ozone reaction with C₇₀ and C₆₀ fullerenes follows the Arrhenius law. The experimental values of activation energy (E_a) and pre-exponential factor (A), like as those of other simple alkenes, are in the order of 2.4-2.6 kcal mol^-1 and (1.2-1.8) × 10⁷ L mol^-1 sec^-1, respectively. They are practically equal for the both fullerenes. It has also been found that the value of the rate constant k of C₇₀ fullerene ozonolysis is higher in comparison to the respective k-value of C₆₀.     

LASER INDUCED MICROCRYSTALLIZATION OF BULK AMORPHOUS Ge15Se85-xTex

Bulk amorphous samples of Ge₁₅Se_85-xTe_x (x = 10,15,20,25) were prepared by a rapid quenching. X-ray diffraction analysis revealed that the as-grown samples were amorphous. In order to understand the laser induced changes, the samples were irradiated with Q-switched Nd: YAG laser pulses of various energy densities (2-50 mJ/cm²). These studies showed that low energy pulses (≤10 mJ/cm²) have no influence on the structure and the transport properties of the samples whereas energy pulses (≥ 10 mJ/cm²) resulted in microcrystallization of the samples. Electrical transport properties such as d.c. electrical conductivity and thermoelectric power were measured as a function of temperature (200 -350 K) and composition. Results were analysed in terms of Small polaron model and two carrier model respectively. The electrical conduction, interestingly, was observed as intrinsic in the entire temperature range of measurements for both as-grown and irradiated samples.     

Optical gain calculation of mid-infrared InAsN/GaSb quantum-well laser for tunable absorption spectroscopy applications

We report on optical gain calculations of a dilute-nitride mid-infrared laser structure designed to be grown on InAs substrate. The active region is composed of several strain-compensated type-II “W”-like InAsN/GaSb/InAsN quantum wells adapted to operate near 3.3 μm at room temperature. For typical injected carrier density σ = 1.1012 cm^− 2, the theoretical laser structure performances reveal a gain value at around 1000 cm^− 1 at 300 K, inducing a modal gain value equal to 50 cm^− 1. Low radiative current densities lower than 100 A/cm² are predicted, indicating that this dilute-nitride structure could operate at 300 K with small threshold current density.     

Influence of a Weak Magnetic Field on Photoconductivity Spectrum of C60 Single Crystal

Comparative research of the excitation photoconductivity spectra (quantum light energy 2-5 eV) of C₆₀ single crystal in and out of magnetic field at the temperature T = 250-350 K has been carried. The spectral evolution at this temperature range is described. It is shown that the spectra changes abrupt at temperature T₁ ∼ 260 K and T₂ ∼ 315 K. An increase in the photoconductivity up to 15% was observed in the magnetic field (B = 0.4 T) within the photon energy range 2.5-4.5 eV. Local photoconductivity peak's appearances in the magnetic field have been proven that the charge transfer excitons take part in a photoconductivity.     

Structure and Defects in Thin C60 Films

Thin C₆₀ films were deposited by vacuum sublimation of soot on single-crystal and amorphous substrates. The absence of higher fullerenes was confirmed by IR, Raman and UV-VIS spectroscopy. X-ray diffraction revealed a high density of stacking faults (probabilities in the range 10^-2), correlated with lattice distortions. Analysis of the UV-VIS absorption bands yielded values of the h_u → t_1g and h_u → t_1u optical gaps.     

Raman Spectroscopy of the Charge Transfer Complex (TTF)x C60 Br8

We report Raman studies on powder samples of the charge transfer complex (TTF)_x C₆₀Br₈ at room temperature. The phonons show considerable softening with respect to the frequencies observed in the Raman spectrum of solid C₆₀ Brg. The strongest mode at 1464 cm^-1 in C₆₀Br₈ is red shifted to a doublet with peaks at 1414 and 1421 cm^-1, implying an average phonon softening Δω of -47 cm^-1. A comparison with the phonon softening of the corresponding A_g(2) mode in alkali-doped C₆₀ (Δω ~ - 36 cm^-1 for A₆C₆₀, A = K, Rb or Cs) suggests that 8 electrons are transferred per C₆₀Br₈ molecule in the charge transfer complex. The mode at 503 cm_--1 in C₆₀Br₈ is shifted upwards, similar to that in A₆ C₆₀ compounds.     

MgO/SrO/La2O3多元添加对(Zr0.8Sn0.2)TiO4微波陶瓷结构性能影响

基于液相促进固相反应烧结机制, 设计MgO/SrO/La₂O₃多元复合添加(Zr_0.8Sn_0.2)TiO₄(ZST)体系, 探究复合添加剂对ZST陶瓷的物相组成、微观结构、烧结特性以及高频介电性能等参数的影响。实验结果表明: 陶瓷的主晶相均为ZST相; 适量添加MgO/SrO/La₂O₃可以有效地降低ZST陶瓷的烧结温度, 获得较优的微波介电性能; 但MgO添加量的增多对材料的综合性能有小幅度的影响; SrO的添加量过大会造成晶粒的不完全生长、瓷体不致密和气孔的增多, 从而导致材料的密度、介电常数和Q×f值的下降; 此外, 添加剂对陶瓷的频率温度系数(τ_f)影响不大。在复合添加0.2wt%MgO、0.6wt%SrO、1.0wt%La₂O₃时, 1300℃保温5 h的ZST陶瓷综合性能优异: ρ=5.14 g/cm³, ε_r=40.11, Q×f=51000 GHz (f=5.61 GHz), τ_f=-2.85×10^-6℃^-1。     

Properties of tantalum oxide thin films grown by atomic layer deposition

Thin tantalum oxide films were deposited using atomic layer deposition from TaCl₅ and H₂O at temperatures in the range 80–500 °C. The films deposited at temperatures below 300 °C were predominantly amorphous, whereas those grown at higher temperatures were polycrystalline containing the phases TaO₂ and Ta₂O₅. The oxygen to tantalum mass concentration ratio corresponded to that of TaO₂ at all growth temperatures. The optical band gap was close to 4.2 eV for amorphous films and ranged from 3.9 to 4.5 eV for polycrystalline films. The refractive index measured at λ = 550 nm increased from 1.97 to 2.20 with an increase in growth temperature from 80 to 300 °C. The films deposited at 80 °C showed low absorption with absorption coefficients of less than 100 cm⁻¹ in the visible region.     

Microwave dielectric characteristics of Ba(Mg1/3Ta2/3)O3 ceramics sintered at low-temperatures

The microwave dielectric properties and microstructures of Ba(Mg_1/3Ta_2/3)O₃ (BMT) ceramics sintered at low temperatures with 2–3 wt.% NaF additives were investigated. BMT ceramics sintered at 1340 °C for 3–12 h showed dielectric constants (_r) of 25.5–25.7, Qf values of 41 500–50 400 GHz and temperature coefficients of the resonator frequency (τ_f) of 10.9–21.4 ppm °C⁻¹. The variation of sintering time almost had no effect on the dielectric constant. The Qf value increased and the τ_f decreased with increasing sintering time. The ordering degree of Mg²⁺ and Ta⁵⁺ at B-sites increased with increasing sintering time.