Characteristics and sensing behavior of electrochemically codeposited polypyrrole–poly(vinyl alcohol) thin film exposed to ethanol vapors

Polypyrrole–poly(vinyl alcohol) (PPy–PVA) composite films were prepared electrochemically by means of codeposition at a constant potential. Their sensing behaviors to various ethanol-vapor concentrations were investigated. Increasing the molar fraction of PVA up to PPy_0.964PVA_0.036 showed an increase of the sensitivity of the composite sensors. However, the sensitivity decreased if further PVA was incorporated. The ethanol-sensing behaviors were also largely dependent upon the electropolymerization charge, ranging from 50 to 200 mC in this investigation. Higher sensitivity was measured from the composite film prepared with a lower electrical charge. For example, a sensitivity of 7.70 mΩ mg⁻¹ L, about 3.3 times the sensitivity of the pristine PPy sensor, was measured by the PPy_0.964PVA_0.036 composite film prepared at 50 mC. However, incorporating PVA into the conducting polymer was at the sacrifice of the response speed as well as the stability of the composite as it was under continuous exposure to ethanol vapor. An adsorption model based on the Langmuir isotherm was used to interpret the sensing behaviors and the equation derived from this model correlated well with the measured sensitivities. The sensing parameters including the adsorption equilibrium constant, K_m, and the resistance change caused by a pseudomonolayer, [m(r₁ − r₂)]/n, were determined and found to decrease with increasing polymerization charge. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2079–2087, 1999     

The effects of surface spin on magnetic properties of weak magnetic ZnLa0.02Fe1.98O4 nanoparticles

In order to prominently investigate the effects of the surface spin on the magnetic properties, the weak magnetic ZnLa_0.02Fe_1.98O₄ nanoparticles were chosen as studying objects which benefit to reduce as possibly the effects of interparticle dipolar interaction and crystalline anisotropy energies. By annealing the undiluted and diluted ZnLa_0.02Fe_1.98O₄ nanoparticles at different temperatures, we observed the rich variations of magnetic ordering states (superparamagnetism, weak ferromagnetism, and paramagnetism). The magnetic properties can be well understood by considering the effects of the surface spin of the magnetic nanoparticles. Our results indicate that in the nano-sized magnets with weak magnetism, the surface spin plays a crucial rule in the magnetic properties.     

Rapid microwave-assisted synthesis and magnetic properties of high-entropy spinel (Cr0.2Mn0.2Fe0.2Co0.2-xNi0.2Znx)3O4 nanoparticles

High-entropy oxide (HEO) has recently become popular because of its unique multifunctional performance. In this study, we developed a novel microwave-assisted method for the production of HEO nanoparticles with the composition (Cr_0.2Fe_0.2Mn_0.2Co_0.2-xNi_0.2Zn_x)₃O₄ (x = 0, 0.05, 0.1, and 0.2). The results revealed that all metallic elements were uniformly distributed throughout the single-phase cubic spinel structure of the HEO nanoparticles. The particle size distributions of four fabricated samples ranged from 10 to 50 nm. Because of its numerous advantages such as the ultrafast and low-temperature fabrication of nanoscale and high-purity products at a relatively low cost, the suggested methodology is an excellent synthesis method. The original HEO spinel (x = 0) achieved saturated magnetization (M_s) and coercivity (H_c) values of 24.3 emu/g and 160 Oe, respectively, at room temperature. Zinc substitution in the HEO composition indicated that M_s and H_c decreased with increasing zinc concentration owing to its non-magnetic nature.     

Structural,optical and magnetic behavior of (Pr,Fe) co-doped ZnO based dilute magnetic semiconducting nanocrystals

The development of ZnO-based dilute magnetic semiconductor nanostructures co-doped with rare-earth and transition metals has attracted substantial attention for spintronics application. In this work, Pr (1%) and Fe (1%, 3%, and 5%) co-doped ZnO nanoparticles (NPs) were synthesized via co-precipitation method, and their structural, morphological, optical, photoluminescence, and magnetic properties were investigated. The single-phase wurtzite hexagonal crystal structure of all samples was detected via X-ray diffraction. Morphological analysis revealed spherical shape of the NPs with an average size in 20–50 nm range. The ultraviolet (UV)–visible measurements showed a redshift in the UV band and a slight change in the bandgap of the co-doped NPs. Fourier transform infrared analysis proved the existence of different functional groups in all synthesized NPs. X-ray photoelectron spectroscopy confirmed that Pr and Fe ions incorporated in the host ZnO lattice exhibit Pr³⁺ and Fe³⁺ oxidation states, respectively. Photoluminescence analysis showed that incorporated ions induce characteristic emission bands and structural defects in the synthesized NPs. Magnetic characterization indicated that the ZnO NPs exhibit a diamagnetic nature. However, the (Pr, Fe) co-doped NPs exhibit ferromagnetism at room temperature because of the interactions between Pr³⁺ and Fe³⁺ ions and trapped electrons mediated by bound magnetic polarons. Excellent optical and magnetic properties of synthesized samples may render them promising candidates for spintronics applications.     

Fe doping and magnetic properties of zincblende SiC ceramics

Fe-doped SiC bulk ceramics were fabricated by hot-pressing, and their magnetic and electronic properties were investigated. Si_1−xFe_xC (x ≤ 0.04) samples having a zincblende crystal structure exhibited ferromagnetic hysteresis at room temperature with the saturation magnetization increasing with x. X-ray diffraction measurements revealed the creation of a Fe₃Si phase in the samples with its density increasing with x. The samples were found to be p-type semiconductors with a hole concentration (electrical resistivity) of ∼10¹⁹ cm⁻³ (∼10⁰ Ω cm) at room temperature. The observed magnetic properties of the samples are mainly ascribed to the presence of ferromagnetic Fe₃Si crystallites. The high carrier concentration of the samples likely implies the existence of acceptors due to individual Fe³⁺ occupation of the Si sites in the lattice. The randomly distributed Fe³⁺ ions represent a minor contribution to the magnetization of the samples through the formation of magnetic polarons with the carriers.     

Blown film extrusion of poly(lactic acid) without melt strength enhancers

Processing strategies were developed to manufacture poly(lactic acid) (PLA) blown films without melt strength enhancers (MSEs). The effects of processing temperature on PLA's melt properties (shear and elongational viscosities), PLA grades, and other processing conditions [ratio of take‐up roller to extruder's rotational screw speeds or processing speed ratio (PSR) and internal air pressures] on film's blow‐up ratio were examined. Experimental results indicate that extrusion‐blown amorphous and semicrystalline PLA films can be successfully manufactured without MSEs by controlling melt rheology through processing temperature and other extrusion processing conditions. PLA processed at lower extrusion temperature had higher melt viscosities, which favored the formation of stable films depending on the PSR and internal air pressure used. Inappropriate control of PSR and internal air pressure led to unstable films with various processing defects such as melt sag, bubble dancing, or draw resonance, irrespective of the lower extrusion processing temperature. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45212.     

Structural,dielectric and ferromagnetic behavior of (Zn,Co) co-doped SnO2 nanoparticles

Nanoparticles of basic composition Sn_0.94Zn_0.05Co_0.01O₂, Sn_0.92Zn_0.05Co_0.03O₂ and Sn_0.90Zn_0.05Co_0.05O₂ were synthesized by chemical precipitation method. The incorporation of Co and Zn in SnO₂ lattice introduced significant changes in the physical properties of all the three nanocrystals. The average particle size estimated from TEM data decreased from 15.71 to 6.41  nm with enhancement in concentration of oxygen vacancies as Co content is increased from 1 to 5 wt%. Increasing Co content enhanced the Sn:O atomic ratio as a result concentration of oxygen vacancies increased. The dielectric study revealed strong doping dependence. The dielectric parameters (ε′, tanδ and σ_ac) increased with increasing Co content and attained maximum values for 5% (Zn, Co) co-doped SnO₂ nanoparticles. The dielectric loss (ε′′) exhibited dispersion behavior and the Debye’s relaxation peaks observed in dielectric loss factor (tanδ), whose intensities increased with increasing Co content. The variation of dielectric properties and ac conductivity revealed that the dispersion is due to Maxwell-Wagner interfacial polarization and hopping of charge carriers between Sn⁺²/Sn⁺³ and Co⁺²/Co⁺³. The large dielectric constant of all samples made them interesting materials for device application. Magnetization measurements (M (H) loops) revealed enhancement in saturation magnetization with doping which is due to the formation of large amount of induced defects and oxygen vacancies in the samples. The present study clearly reveals doping dependent properties and the oxygen vacancies induced ferromagnetism in Zn, Co co-doped SnO₂ nanoparticles having applications in ultra-high dielectric materials, high frequency devices and spintronics.     

Effect of Fe doping on the magnetic properties of PbPdO2 nanograin film fabricated by sol-gel method

The single-phase Fe-doped PbPdO₂ film was prepared using a sol-gel spin-coating method. The film had a nanograin structure consisting of compacted particles with an average crystallization size of about 35.2 nm. Large amount of Pb vacancies were found in the film. The valences of the Pb, Pd and Fe ions of the film were confirmed to be near 2+, 2+ and 3+, respectively. The additional electron provided by Fe³⁺ and the high ionization energy of Fe³⁺ ensure the stability of the valence of doped Fe ions. The measurement of hysteresis loops and the theoretical fitting of the zero-field-cooled and field-cooled magnetization versus temperature curve indicated that the ferromagnetism and the paramagnetism coexist in the Fe-doped PbPdO₂. And the ferromagnetism persisted up to 380 K. A bound magnetic polaron model based on the Pb vacancies, the carriers and the doped Fe ions was utilized to account for the origin of the film's ferromagnetism. The isolated Fe ions or magnetic polarons were believed to be responsible for the paramagnetism in the film.     

多单体熔融接枝天然橡胶及其性能的研究

以甲基丙烯酸缩水甘油酯（GMA）为接枝单体，苯乙烯（St）为接枝共单体，过氧化二异丙苯（DCP）为引发剂，通过熔融接枝法制备接枝天然橡胶[NR-g-（GMA-co-St）]。研究了GMA、St及DCP用量和接枝温度对NR的接枝率及其力学性能的影响。结果表明，GMA、St和DCP质量分数分别为8％、4％和0．3％，接枝温度为160℃时，NR-g-（GMA—co—St）的接枝率最高，综合力学性能最好；St的加入能明显提高NR的接枝率，并能减轻NR的降解；红外光谱的分析证实了GMA已接枝到天然橡胶分子链上。     

A review of the structure,magnetic and electrical properties of bismuth ferrite (Bi2Fe4O9)

Nowadays, investigations on the materials with multiferroic properties are in progress. These materials compromise simultaneous electric and magnetic properties. Ferrite Bismuth (FB) is one of the ceramic materials that enjoy this property and possesses three different crystalline structures (perovskite BiFeO₃, selenite Bi₂₅FeO₄₀ and mullite Bi₂Fe₄O₉). In this review, first, the crystalline structure and the electric and magnetic properties of Bi₂Fe₄O₉ are studied, and then, the effects of adding dopants to the ferrite are discussed. Mullite-type bismuth ferrite (Bi₂Fe₄O₉) as a spin frustrated multiferroic has potential for magnetoelectric coupling, and it might be an appropriate alternative for some of the multiferroics that suffer from a weak magnetoelectric coupling.     

Synthesis, structure and magnetic properties of a novel lead(II) complex containing nitronyl nitroxide radicals

The lead(II) complex with nitronyl nitroxide, [Pb(NIT2Py)₂(NO₃)₂] [NIT2Py = 2-(2′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], has been prepared and characterized by magnetic and single-crystal X-ray diffraction studies. In the complex, the lead(II) ion is coordinated with two bidentate nitronyl nitroxide and two nitrate anions. The lead(II) ion shows seven-coordinate geometry. Magnetic susceptibility data for the title complex has been measured in the range 5–300 K. There are antiferromagnetic interaction between the coordinated nitronyl nitroxides (J = −19.35 cm⁻¹) and intermolecular ferromagnetic interactions. Thus, we observe the sixth periodic IVA group metal element Pb(II) ion providing an effective pathway for the magnetic exchange interaction between nitronyl nitroxide radicals.     

热熔型纸塑复合预涂膜的研制

以EVA弹性体为主体材料,配以适宜的增粘树脂及其他助剂,制成热熔胶粘剂并涂于BOPP或聚酯膜上,用于纸塑复合。讨论了各种基料对热熔胶软化点、熔融粘度的影响。该预涂膜性能优良,无毒无污染,复合工艺简单,可提高生产效率。     

Solution combustion synthesis of new metal borophosphates (Fe1-xCrx)2B(PO4)3: Structural,thermal, surface,and magnetic properties

The new borophosphates were successfully synthesized by solution combustion synthesis assisted with glycine. The obtained materials were systematically characterized by Fourier-transform infrared spectroscopy, X-ray powder diffraction, UV–visible spectroscopy, thermogravimetric analysis, scanning electron microscopy, Brauner-Emmett-Teller surface area, and magnetometry. The Rietveld refinements indicated that Fe₂B(PO₄)₃ is a hexagonal, space group P63/m with a = b = 8.029 and c = 7.408. As Cr substitutes the Fe atoms, there is a significant decrease in the lattice parameters. When all Fe atoms are replaced by Cr, Cr₂B(PO₄)₃ is formed and the structure turns out to be a trigonal, space group P3 with a = b = 7.950 and c = 7.360. The materials are thermally stable and demonstrate paramagnetic behavior at room temperature. The magnetization increases as the iron content increases because of the high magnetic moment of the iron ion. Temperature-dependent magnetic measurements reveal that Fe₂B(PO₄)₃ has a Néel transition at 30 K and the Néel temperature decreases with Cr substitution.     

A novel chloro-bridged tetranuclear cadmium(II) cluster with pyridyl-substituted nitronyl nitroxide: structure and magnetic properties

A tetranuclear cadmium(II) complex of 2(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H-imidazol-1-oxy 3-N-oxide (NIToPy) with CdCl₂,[Cd₄Cl₈(NIToPy)₄], has been structurally and magnetically characterized. The structure is based on a novel chloro-bridged tetranuclear cadmium quasi-cubane cluster, in which each cadmium atom is chelated by one NIToPy radical, and coordinated with four bridging chlorine atoms. The temperature dependence of the magnetic susceptibility measurements shows a weak ferromagnetic coupling between the radicals. An excellent simulation of the experimental data with the prism type four spins Hamiltonian H=−2J₁(S₁S₂+S₂S₃+S₃S₄+S₁S₄)−2J₂S₂S₄ obtained the parameters: J₁=1.12 cm⁻¹, J₂=−0.20 cm⁻¹, and g=2.04.     

Structural,electrical, magnetic and magnetoelectric properties of Fe doped BaTiO3 ceramics

In the present work structural, electrical, magnetic and magnetodielectric properties of BaTi_1−xFe_xO₃ (0%≤x≤10%) ceramics have been investigated. X-ray diffraction (XRD) study reveals that the coexistence of tetragonal and hexagonal phases is strongly influenced by Fe doping concentration. The increase in Fe-doping content leads to the development of hexagonal phase along with an increase in average grain size. A reduction in the dielectric properties is also observed. All BaTi_1−xFe_xO₃ (BTFO) compositions exhibit ferroelectric behavior at room temperature. Remnant polarization (P_r) for pure BaTiO₃ (BTO) has been found to be 7.50 µC/cm² and further decreases with an increase in the Fe concentration. All Fe doped samples exhibit ferromagnetic ordering with saturation magnetization (M_s) being 26 memu/g for x=2.5%. Further, at x=5%, it decreases and thereafter again increases with Fe concentration. The magnetodielectric coefficient increases with Fe doping concentration and highest value found to be 2.80 at x=2.5%.     

Effect of Ni2+ substitution on structural,magnetic, dielectric and optical properties of mixed spinel CoFe2O4 nanoparticles

Nanoparticles of Co_1−xNi_xFe₂O₄ with x=0.0, 0.10, 0.20, 0.30, 0.40 and 0.50 were synthesized by co-precipitation method. The structural analysis reveals the formation of single phase cubic spinel structure with a narrow size distribution between 13–17 nm. Transmission electron microscope images are in agreement with size of nanoparticles calculated from XRD. The field emission scanning electron microscope images confirmed the presence of nano-sized grains with porous morphology. The X-ray photoelectron spectroscopy analysis confirmed the presence of Fe²⁺ ions with Fe³⁺. Room temperature magnetic measurements showed the strong influence of Ni²⁺ doping on saturation magnetization and coercivity. The saturation magnetization decreases from 91 emu/gm to 44 emu/gm for x=0.0–0.50 samples. Lower magnetic moment of Ni²⁺ (2 µ_B) ions in comparison to that of Co²⁺ (3 µ_B) ions is responsible for this reduction. Similarly, overall coercivity decreased from 1010 Oe to 832 Oe for x=0.0–0.50 samples and depends on crystallite size. Cation distribution has been proposed from XRD analysis and magnetization data. Electron spin resonance spectra suggested the dominancy of superexchange interactions in Co_1−xNi_xFe₂O₄ samples. The optical analysis indicates that Co_1−xNi_xFe₂O₄ is an indirect band gap material and band gap increases with increasing Ni²⁺ concentration. Dispersion behavior with increasing frequency is observed for both dielectric constant and loss tangent. The conduction process predominantly takes place through grain boundary volume. Grain boundary resistance increases with Ni²⁺ ion concentration.     

Solid state structure and mechanical properties of melt mixed poly(trimethylene terephthalate)/polycarbonate blends

Poly(trimethylene terephthalate) (PTT)/poly (carbonate of bisphenol A) (PC) blends were obtained in the melt state by direct injection molding and also by extrusion followed by injection molding. The blends rich in PTT were monophasic, while the blends rich in PC were biphasic with the two components of the blends present in both phases. Both the monophasic and biphasic blends were partially miscibilized, and also partially reacted, as observed by FTIR. The extent of the reaction was greater in previously mixed blends. The observed synergism in the modulus of elasticity was attributed to the increased orientation of the blend components upon blending. Although decreases in elongation at break were observed and attributed to degradation of PTT, the blends were clearly ductile and compatible. This was a consequence of either their monophasic structure, or of the presence of the two components in the two phases of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhancement in electrical and magnetic properties of (Li0.5Ga0.5)2+ and (Li0.5Er0.5)2+-Modified BiFeO3-BaTiO3 ceramics

Effects of (Li_0.5Ga_0.5)²⁺ and (Li_0.5Er_0.5)²⁺ doping on the phase structure, electrical, and magnetic properties of 0.75BiFeO₃-0.25BaTiO₃ (BFO-BT) ceramics were investigated and analyzed. X-ray diffraction measurements suggested a rhombohedral distorted perovskite structure and no structural transformation with the increasing doping content. Rietveld refinement results revealed that (Li_0.5Ga_0.5)²⁺ ions were more susceptible to replace the B-sites and (Li_0.5Er_0.5)²⁺ ions tended to substitute the A-sites. A significant improvement in the dielectric loss, ferroelectricity, and magnetization was observed for both (Li_0.5Ga_0.5)²⁺ and (Li_0.5Er_0.5)²⁺-modified BFO–BT ceramics without the addition of MnO₂ compared to undoped ceramic samples. Remnant magnetization (M_r) of 0.35 emu/g was reached for LG6. The enhanced magnetic properties were related to the suppressed cycloidal spin structure, the presences of the local lattice disorder and the magnetic impurities induced by the (Li_0.5Ga_0.5)²⁺ and (Li_0.5Er_0.5)²⁺ substitution.