Synthesis,characterization, thermal stability,conductivity and band gap of oligo-4-[(2-hydroxybenzylidene)amino]benzoic acid

In this study, the oxidative polycondensation reaction conditions of 4-[(2-hydroxybenzylidene)amino]benzoic acid (4-HBAB) by using oxidants such as air O₂, H₂O₂ and NaOCl were studied in an aqueous alkaline medium between 40 and 90 °C. The structures of the synthesized monomer and oligomer were confirmed by FT-IR, UV–vis, NMR and elemental analysis. The characterization was made by TG-DTA, size exclusion chromatography (SEC) and solubility tests. At the optimum reaction conditions, the yield of oligo-4-[(2-hydroxybenzylidene)amino]benzoic acid (O-4-HBAB) was found to be 68% (for air O₂ oxidant), 70% (for air H₂O₂ oxidant) 53% (for NaOCl oxidant). According to the SEC analysis, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of O-4-HBAB were found to be 932, 1469 g mol⁻¹ and 1.576, using H₂O₂, and 1895, 2560 g mol⁻¹ and 1.354, using air O₂ and 2320, 3015 g mol⁻¹ and 1.300, using NaOCl, respectively. According to TG analysis, the weight losses of 4-HBAB and O-4-HBAB were found to be 96.86% and 73.10% at 1000 °C, respectively. O-4-HBAB was shown higher stability against thermal decomposition. Also, electrical conductivity of the O-4-HBAB was measured, showing that the polymer is a typical semiconductor. Electrochemical HOMO, LUMO and energy gaps (E_g) of 4-HBAB and O-4-HBAB were found to be −6.28, −6.36; −2.39, −2.64; 3.89 and 3.72 eV, respectively. According to UV–vis measurements, optical band gap (E_g) of 4-HBAB and O-4-HBAB were found to be 3.23 and 3.09 eV, respectively.     

The synthesis and characterization of new oligo(polyether)s with Schiff base type

New oligo(polyether) ligands with Schiff base type were synthesized by the reaction of diethyleneglycol bis(2-aminophenyl ether) and triethyleneglycol bis(4-aminophenyl ether) with oligosalicylaldehyde (OSA). OSA was synthesized from the oxidative polycondensation of salicylaldehyde (SA) with air in an aqueous alkaline medium at 90 °C. The products were characterized by ¹H-NMR, ¹³C-NMR, FT-IR, UV–Vis and elemental analysis. The number average molecular weight, M_n, mass average molecular weight, M_w, and polydispersity index values, PDI, of OSA, graft oligo[1,5-di(N-2-oxyphenyl-salicylidene)-3-oxapentane] (compound 4) and graft oligo[1,8-di(N-4-oxyphenyl-salicylidene)-3,6-oxaoctane] (compound 5) were found to be 1690 g mol⁻¹, 5150 g mol⁻¹, 3.05, 1100 g mol⁻¹, 5400 g mol⁻¹, 4.90 and 1100 g mol⁻¹, 5600 g mol⁻¹, 5.01, respectively. TG and DTA analyses were shown to be stable of oligo(polyether) ligands with Schiff base type against thermo-oxidative decomposition. The weight loss of oligo(polyether) ligands with Schiff base type (compounds 4 and 5) were found to be 52 and 56% at 1000 °C, respectively.     

Crystal structure and physical properties of a magnetic molecular conductor (EDO-TTFVODS)2FeCl4

Crystal structure, and electrical conducting and magnetic properties of a radical cation salt of EDO-TTFVODS with magnetic FeCl₄^? ion, (EDO-TTFVODS)₂FeCl₄ (EDO-TTFVODS = ethylenedioxytetrathiafulvalenoquinone-1,3-diselenolemethide) are reported. In this salt, there are two independent donor molecules formed two different layers A and B, and the counter FeCl₄^? ions layer is sandwiched between two donor layers A and B along the b-axis. The donor molecules form the one-dimensional columns along the a-axis in both donor layers. This salt shows high conductivity at room temperature (σ_RT = 25 S cm^?1) and a metallic behavior down to ca. 80 K, where a metal–insulator transition however occurs. The magnetic susceptibility obeys a Curie–Weiss law (Curie constant C = 4.42 emu K mol^?1 and Weiss temperature Θ = ?1.5 K), without any magnetic ordering down to 1.8 K. This result suggests the weak antiferromagnetic interaction between the d spins of FeCl₄^? ions.     

Magnetic,electronic and thermodynamic properties of the heavy fermion compound CeNiAl4

We have carried out the magnetic susceptibility, electrical resistivity, specific heat, thermoelectric power and X-ray photoemission spectroscopy (XPS) measurements for CeNiAl₄. The magnetic susceptibilities have revealed a Curie–Weiss behavior above 30 K with a large negative paramagnetic Curie temperature θ_P = ?66 K and an effective moment of 2.45μ_B. The f-occupancy and the coupling between the f level and the conduction states are derived from XPS to be about 0.83 and ～40–64 meV, respectively. The valence state of the Ce ion is close to 3+. Extrapolation of the lowest temperatures range of C/T(T²) yields the electronic specific heat coefficient γ = 0.5 J mol^?1 K^?2. In combination with the thermoelectric power and resistivity data, a heavy fermion state is confirmed in CeNiAl₄.     

Creep behavior and its correlation with defect chemistry of La0.58Sr0.4Co0.2Fe0.8O3−δ

The creep behavior of La_0.58Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) perovskite was studied in the temperature range 750–950 °C in air and vacuum (P_O2 ≈ 4 mbar). A transition in the apparent activation energy was found between 800 and 850 °C for both oxygen partial pressures. The apparent activation energy is ～250 kJ mol^?1 for the temperature range 700–800 °C under vacuum (P_O2 ≈ 4 mbar) and ～480 kJ mol^?1 for 850–950 °C in both atmospheres. Above 850 °C, the creep rate of LSCF is higher in vacuum than in air although the same cubic structure exists. The stress exponent of the creep law is in the range 1.9–2.5 for all temperatures, which excludes a transition of creep mechanism. It is suggested that, below 800 °C, cation vacancies originate from the necessary balance with the substituted cations in LSCF, and the determined activation energy reflects the energy barrier for cation migration via these vacancies. Above 850 °C, additional vacancies appear to be formed intrinsically, and the activation energy represents the sum of the thermally activated formation energy of cation vacancies and migration energy of cations.     

Non-isothermal oxidation of ceramic nanocomposites using the example of Ti–Si–C–N powder: Kinetic analysis method

A method of kinetic analysis applicable to non-isothermal oxidation processes of ceramic nanocomposites is presented using Ti–Si–C–N powder as the substrate. The nanoparticle size and phase composition were determined using high-resolution transmission electron microscopy and X-ray diffraction (XRD). Thermogravimetric measurements were carried out for powder samples in dry air in the temperature range 298–1770 K. The following heating rates were applied: 3, 5, 10, 20 K min⁻¹. Mass spectrometry was used to analyze gaseous oxidation products and solid products were identified by the XRD technique. The Coats–Redfern equation was applied for the kinetic analysis. For each stage of the oxidation kinetic models, the best accuracy was achieved using a series of criteria, and then the A and E parameters of the Arrhenius equations were estimated. Both linear regression and artificial neural networks were applied in testing kinetic models.     

Densification and grain growth during early-stage sintering of Ce0.9Gd0.1O1.95−δ in a reducing atmosphere

The present work investigates the processes of densification and grain growth of Ce_0.9Gd_0.1O_1.95?δ (CGO10) during sintering under reduced oxygen partial pressure. Sintering variables were experimentally characterized and analyzed using defect chemistry and sintering constitutive laws. Based on the results achieved, the grain size–relative density relationship, the densification rate and the grain-growth rate were determined. The activation energies for densification and grain growth were evaluated, and the dominant densification mechanism was indicated. For comparison, the densification behavior of CGO10 sintered in air was also studied. Accelerated densification was observed in early-stage sintering of CGO10 in a reducing atmosphere. This might be attributed to the oxygen vacancies generated by the reduction of Ce⁴⁺ to Ce³⁺ in the reducing atmosphere, which facilitate the diffusion of ions through the lattice. The densification activation energy of CGO10 in the reducing atmosphere was evaluated to be 290 ± 20 kJ mol^?1 in the relative density range of 0.64–0.82, which was much smaller than that of CGO10 sintered in air (770 ± 40 kJ mol^?1). The grain-growth activation energy of CGO10 sintered in the reducing atmosphere was evaluated to be 280 ± 20 kJ mol^?1 in the grain size range of 0.34–0.70 μm. The present work describes a systematic investigation of sintering behavior of CGO10 under reduced oxygen partial pressure, which contributes to the first known determination of the fundamental parameters associated with densification and grain growth during early-stage sintering of CGO10 in a reducing atmosphere.     

Structure of a new ternary compound with high magnesium content,so-called Gd13Ni9Mg78

The magnesium-rich composition Gd₁₃Ni₉Mg₇₈ was synthesized from its constituent elements in sealed tantalum tubes in an induction furnace. X-ray diffraction, electron probe microanalysis and dark-field transmission electron microscopy (TEM) images revealed a new compound with a composition ranging from Gd_10–15Ni_8–12Mg_72–78 and low crystallinity. In order to increase the crystallinity, different experimental conditions were investigated for numerous compounds with the initial composition Gd₁₃Ni₉Mg₇₈. In addition, several heat treatments (from 573 to 823 K) and cooling rates (from room temperature quenched down to 2 K h^?1) have been tested. The best crystallinity was obtained for the slower cooling rates ranging from 2 to 6 K h^?1. From the more crystallized compounds, the structure was partially deduced using TEM and an average cubic structure with lattice parameter a = 4.55 Å could be assumed. A modulation along both a¹ and b¹ axis with vectors of modulation q1 = 0.42a¹ and q2 = 0.42b¹ was observed. This compound, so-called Gd₁₃Ni₉Mg₇₈, absorbs around 3 wt.% of hydrogen at 603 K, 30 bars and a reasonable degree of reversibility is possible, because after the first hydrogenation, irreversible decomposition into MgH₂, GdH₂ and NiMg₂H₄ has been shown. The pathway of the reaction is described herein. The powder mixture after decomposition shows an interesting kinetics for magnesium without ball milling.     

Hydrogen diffusion and trapping in a precipitation-hardened nickel–copper–aluminum alloy Monel K-500 (UNS N05500)

Hydrogen uptake, diffusivity and trap binding energy were determined for the nickel–copper–aluminum alloy Monel K-500 (UNS N05500) in several conditions. The total atomic hydrogen (H) concentration increased from 0 to 132 wppm as the hydrogen overpotential decreased to ?0.5 V in alkaline 3.5% NaCl electrolyte at 23 °C. The room-temperature H diffusion coefficient ranged from 0.9 to 3.9 × 10^?14 m² s^?1 for single-phase solid solution, aged, and cold worked then aged microstructures. Diffusivity was independent of lattice H concentration but depended weakly on metallurgical condition, with slower H diffusion after aging. The apparent activation energy for H diffusion was in the range of 29–41 ± 1.5 kJ mol^?1 at the 95% confidence level. The lower value approached nearly perfect lattice transport, while the high value was strongly influenced by traps of low-to-intermediate strength. Atomic hydrogen trapping at metallurgical sites, strongly suggested to be spherical-coherent γ′ (Ni₃Al) precipitates, was evident in the aged compared to the solution heat treated + water-quenched condition. Both thermal desorption and classical Oriani trap state analyses confirmed that the apparent hydrogen trap binding energy interpreted as Ni₃Al (10.2 ± 4.6 kJ mol^?1) interfaces was significantly less than the activation energy for perfect lattice diffusion (25.6 ± 0.5 kJ mol^?1) in this nickel-based alloy system.     

Cationic and radical polymerization of N-vinyl-2-phenylpyrrole: Synthesis of electroconducting,paramagnetic and fluorescent oligomers

Cationic polymerization of N-vinyl-2-phenylpyrrole (catalysts: Me₃SiCl, CF₃COOH, BF₃·OEt₂, HCl, WCl₆, FeCl₃, complex LiBF₄–dimethoxyethane, catalysts concentration 1–2 wt%, 20–70 °C, 24–48 h) affords oligomers (molecular weight 1400–1700) of a unexpected structure with alternating 2-phenylpyrrole and ethylydene units, the yields reaching 63%. The oligomers structure has been supported by isolation and identification of the corresponding dimer, N-vinyl-2-phenyl-5-[N-(2-phenyl-1H-pyrrol-1-yl)ethyl]-1H-pyrrole. Radical polymerization of the same monomer (AIBN, 1.5–4 wt%, 60–80 °C, 40–60 h or UV irradiation or both) gives oligomers (molecular weight 2100–3000) of normal structure having polyethene backbone with pendant 2-phenylpyrrole groups in up to 40% yields. The oligomers of both types are semiconductors (1.3 × 10^?6–3.6 × 10^?6 S/cm) after doping with I₂, paramagnetic (4.2 × 10¹⁷–8.7 × 10¹⁷ g^?1) and fluorescent in a near UV region (λ 355–363 nm, acetonitrile).     

Sintering behavior and non-linear properties of ZnO varistors processed in microwave electric and magnetic fields at 2.45 GHz

A study of the densification behavior and grain growth mechanisms of ZnO-based varistors composed of 98 mol.% ZnO–2 mol.% (Bi₂O₃, Sb₂O₃, Co₃O₄, MnO₂) has been carried out. The pressed samples were sintered in microwave electric (E) and magnetic (H) fields using a single-mode cavity of 2.45 GHz. The effect of the sintering temperature (900–1200 °C), holding time (5–120 min) and sintering mode (E, H) on the microstructure and electrical properties of the sintered varistor samples were investigated. The grain growth kinetics was studied using the simplified phenomenological equation Gⁿ = kte^(?Q/RT). The grain growth exponent (n) and apparent activation energy (Q) values were estimated for both electric and magnetic heating modes and were found to be n = 3.06–3.27, Q = 206–214 kJ mol^?1, respectively. The lower value of n estimated in the E field was attributed to a volume diffusion mechanism, whereas the higher n value in the H field sintering was correlated mainly to a combined effect of volume and surface diffusion processes. Samples sintered in the H and E fields showed high final densities. Moreover, the ones sintered in the H field presented slightly higher density values and bigger grains for all sintering temperatures than E field heated ones. The optimal sintering conditions were achieved at 1100 °C for a 5 min soaking time for both H and E field processed samples, where respectively densities of 99.2 ± 0.5% theoretical density (TD) and 98.3 ± 0.5% TD along with grain size values of G = 7.2 ± 0.36 μm and G = 6.6 ± 0.33 μm were obtained. Regarding the electrical properties, breakdown voltage values as high as 500–570 V mm^?1 were obtained, together with high non-linear coefficients α = 29–39 and low leakage currents (J_l ≈ 5 × 10^?3 mA cm^?2), respectively, for E and H field sintered varistor samples. Moreover, samples sintered in an H field systematically exhibited higher breakdown voltage values compared to the ones sintered in the E field. This was attributed to an improved coupling between the H field and the present dopants within the ZnO matrix, this latter being mostly semiconductive, thus leading to an enhanced reactivity and improved properties of the electrostatic barrier.     

Nitric oxide sensing by cytochrome c bonded to a conducting polymer modified glassy carbon electrode

A nitric oxide biosensor based on cytochrome c (an heme protein) covalently immobilized to poly(5-amino-1-naphthol) by using cyanuric chloride as a bridge was developed. The immobilization was studied by cyclic voltammetry and quartz crystal microbalance. The nitric oxide detection as a function of poly(5-amino-1-naphthol) amount was recorded, and the best result was obtained with the electrode prepared by 70 cycles. The sensitivity and detection limit were 0.015 μA cm^?2/μmol L^?1 and 2.85 μmol L^?1, respectively.     

Controlling of silicon–insulator–metal junction by organic semiconductor polymer thin film

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO₂/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 10⁵ at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the I–V characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO₂/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V_oc) along with a short circuit current (I_sc). This suggests that the n-Si/SiO₂/MEH-PPV/Al diode is a photovoltaic device with V_oc = 0.456 V and J_sc = 7.89 × 10^?8 A/cm² values under 100 mW/cm² illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D_it values with time constant τ_it of the diode under dark and illumination conditions were found to be 2.53 × 10¹⁰ eV^?1 cm^?2 with 5.09 × 10^?5 s and 2.50 × 10¹⁰ eV^?1 cm^?2 with 8.27 × 10^?5 s, respectively. The obtained results indicate that the n-Si/SiO₂/MEH-PPV/Al diode is a photo-sensitive diode.     

Thermal expansion of the V5Si3 and T2 phases of the V–Si–B system investigated by high-temperature X-ray diffraction

The thermal expansion anisotropy of the V₅Si₃ and T₂-phase of the V–Si–B system were determined by high-temperature X-ray diffraction from 298 to 1273 K. Alloys with nominal compositions V_62.5Si_37.5 (V₅Si₃ phase) and V₆₃Si₁₂B₂₅ (T₂-phase) were prepared from high-purity materials through arc-melting followed by heat-treatment at 1873 K by 24 h, under argon atmosphere. The V₅Si₃ phase exhibits thermal expansion anisotropy equals to 1.3, with thermal expansion coefficients along the a and c-axis equal to 9.3 × 10^?6 K^?1 and 11.7 × 10^?6 K^?1, respectively. Similarly, the thermal expansion anisotropy value of the T₂-phase is 0.9 with thermal expansion coefficients equal to 8.8 × 10^?6 K^?1 and 8.3 × 10^?6 K^?1, along the a and c-axis respectively. Compared to other isostructural silicides of the 5:3 type and the Ti₅Si₃ phase, the V₅Si₃ phase presents lower thermal expansion anisotropy. The T₂-phase present in the V–Si–B system exhibits low thermal expansion anisotropy, as the T₂-phase of the Mo–Si–B, Nb–Si–B and W–Si–B systems.     

Transport studies of NH4NO3 doped methyl cellulose electrolyte

This work reports on the transport properties of NH₄NO₃ doped methyl cellulose (MC) polymer electrolyte. The polymer electrolyte films were prepared by the technique of solvent casting. The highest room temperature conductivity of MC doped with 25 wt.% NH₄NO₃ is 2.10 ± 0.37 × 10^?6 S cm^?1. Conductivity–temperature relationship obeys the Vogel–Tamman–Fulcher (VTF) rule from which the glass transition temperature, T_g was evaluated. The mobility, μ and number density of charge carrier, n were calculated using the Rice and Roth model.     

Superplastic characteristic of Mn–Si–Cr alloyed ultrahigh carbon steel realized through a novel process

A novel process based on simple heat treatment was developed in order to explore the superplastic characteristic of Mn–Si–Cr alloyed ultrahigh carbon steel. After austenitizing at A₁ ? A_cm and slow cooling, a microstructure with superplastic “potential” was obtained. The microstructure with superplastic “potential”, mainly composed of martensite and spherical carbides, could transform to a fine (austenite + ferrite + spherical carbides) microstructure beneficial for superplasticity during subsequent warm deformation at just below A₁. The superplastic characteristic during warm deformation is as follows: flow stress stays at 30–50 MPa and the m value reaches 0.4–0.5 at a strain rate of 10^–4–2 × 10^?4 s^?1. The novel process has two advantages: ultrahigh strength (HRC52) and excellent ductility (the reduction of area ～45%) are ensured after superplastic forming without the need of supplementary heat treatment; internal stress in the microstructure obtained after superplastic forming can be avoided to a great extent.     

A study of the densification mechanisms during spark plasma sintering of zirconium (oxy-)carbide powders

Zirconium oxycarbide powders with controlled composition ZrC_0.94O_0.05 were synthesized using the carboreduction of zirconia. They were further subjected to spark plasma sintering (SPS) under several applied loads (25, 50, 100 MPa). The densification mechanism of zirconium oxycarbide powders during the SPS was studied. An analytical model derived from creep deformation studies of ceramics was successfully applied to determine the mechanisms involved during the final stage of densification. These mechanisms were elucidated by evaluating the stress exponent (n) and the apparent activation energy (E_a) from the densification rate law. It was concluded that at low macroscopic applied stress (25 MPa), an intergranular glide mechanism (n ? 2) governs the densification process, while a dislocation motion mechanism (n ? 3) operates at higher applied load (100 MPa). Transmission electron microscopy observations confirm theses results. The samples treated at low applied stress appear almost free of dislocations, whereas samples sintered at high applied stress present a high dislocation density, forming sub-grain boundaries. High values of apparent activation energy (e.g. 687–774 kJ mol^?1) are reached irrespective of the applied load, indicating that both mechanisms mentioned above are assisted by the zirconium lattice diffusion which thus appears to be the rate-limiting step for densification.     

Iridium(III) complexes with cyclometalated styrylbenzoimidazole ligands: Synthesis,electrochemistry and as highly efficient emitters for organic light-emitting diodes

Two phosphorescent iridium complexes (psbi)₂Ir(acac) and (ppbi)₂Ir(acac) (psbi = 1-phenyl-2-styryl-1H-benzo[d]imidazole, ppbi = 1-phenyl-2-(1-phenylprop-1-en-2-yl)-1H-benzo[d]imidazole, acac = acetylacetonate) were synthesized, and their photophysical, electrochemical and electroluminescent properties were also studied. Organic light-emitting devices with these two complexes as dopant emitters having the structure ITO/NPB (10 nm)/TCTA (20 nm)/x%Ir:CBP (y nm)/BCP (10 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The device based on (psbi)₂Ir(acac) exhibited a maximum brightness of 56,162 cd m^?2, while the device based on (ppbi)₂Ir(acac) gave a maximum brightness of 31,232 cd m^?2. At high brightness of 1000 cd m^?2 and 10,000 cd m^?2, high current efficiencies of 25.7 cd A^?1 and 20.7 cd A^?1 were achieved, respectively, for the (psbi)₂Ir(acac)-based EL device. For the EL device based on (ppbi)₂Ir(acac), current efficiencies of 20.1 cd A^?1 at 1000 cd m^?2 and 14.2 cd A^?1 at 10,000 cd m^?2 were observed.     

Electrochemical synthesis and corrosion behavior of polyaniline-benzoate coating on copper

Electrochemical polymerization of polyaniline (PANI) coating on copper electrode was performed galvanostatically in the current density range between 0.50 and 1.25 mA cm^?2, from aqueous solution of 0.3 mol dm^?3 sodium benzoate and 0.2 mol dm^?3 aniline. The corrosion behavior of PANI coated copper and copper electrode exposed to 0.5 mol dm^?3 sodium chloride solution was investigated by potentiodynamic and electrochemical impedance spectroscopy techniques. It was observed that thin PANI (5 μm) coating had provided efficient protection (～96%) to copper in 0.5 mol dm^?3 sodium chloride solution. Unusual initial impedance behavior to that normally observed with conventional organic coatings was attributed to dedoping of benzoate anions from the polymer coating.     

Crystal structure and properties of the new ternary compound Mg21Ga5Hg3

The crystal structure of a new ternary compound Mg₂₁Ga₅Hg₃ has been studied using X-ray powder diffraction data by Rietveld method. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for sample composition examination. The compound crystallizes in the Ge₈Pd₂₁ structure type (space group I4₁/a, a = 1.45391(5) nm, c = 1.15955(4) nm, Z = 4). All interatomic distances indicate metallic type bonding. The average thermal expansion coefficients α_a, α_c and α_V of Mg₂₁Ga₅Hg₃ are 2.60 × 10^?5 K^?1, 2.02 × 10^?5 K^?1, and 7.25 × 10^?5 K^?1, respectively. Electrical resistivity of Mg₂₁Ga₅Hg₃ was measured between 5 and 300 K.