Influence of injection molding on the electrical properties of polyamide 12 filled with multi-walled carbon nanotubes

Microinjection-molded and compression-molded polyamide (PA12) matrix composites filled with 0.67, 1.33, 2 and 4 wt% multi-walled carbon nanotubes (MWNTs) were prepared from twin-screw extruded pellets. The compression molded samples have an electrical percolation threshold close to 1.2 wt%. Coupled rheological and electrical measurements show that their electrical properties start decreasing as soon as shear begins and are partially restored during flow, suggesting successively breakage and reconstruction of a percolating network. On the other hand, the electrical properties of the microinjection molded composites are close to the matrix ones, showing that cooling is too fast for the MWNTs to form a network. There is some electrical anisotropy in these composites, as evidenced by a greater conductivity measured in the flow direction. However polarized Raman spectroscopy analysis does not reveal a significant orientation of the MWNTs.     

Influence of Eu doping on the structural,electrical and optical behavior of Barium Zirconium Titanate ceramic

The influence of Eu³⁺ doping on the structural, dielectric and optical behavior of Barium Zirconium Titanate (BZT) with general formula Ba_1?xEu_2x/3Zr_0.05Ti_0.95O₃ (x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05) has been investigated in the present study. The X-ray diffraction (XRD) data show a phase transition from orthorhombic to tetragonal symmetry due to the incorporation of Eu³⁺ ions in BaZr_0.05Ti_0.95O₃ matrix. A secondary phase of Eu₂Ti₂O₇ is observed for the composition with x ≥ 0.03. The Raman spectroscopic study confirms the structural change as observed in XRD, while the Fourier transformation infra red (FT-IR) spectra reveal that Eu³⁺ doping in BZT creates vacancies in the system. The temperature dependent dielectric study shows that the transition temperature and maximum dielectric constant decrease with increase in Eu³⁺content. It is observed that the dielectric diffuseness increases up to x≤0.02 followed by a decrease at higher concentrations of Eu³⁺. The optical behavior of prepared samples is studied through UV–visible spectroscopy, and it is found that the optical band-gap value increases with Eu³⁺ concentration up to 2% and then decreases for higher concentrations (x > 2%).     

Influence of Mn-substitution on the structure and low-temperature electrical conduction properties of PrCoO3

Rare earth cobalt perovskite oxide (LnCoO₃) is one kind of complex metal oxides and has a wide variety of applications. The performance of LnCoO₃ is controlled by its electrical conduction, and therefore it is essential to study the behaviour of electrical conduction in LnCoO₃ and elucidate the corresponding conduction mechanism. In this work, a series of PrCo_1−xMn_xO₃(x = 0, 0.05, 0.1, 0.15, 0.2) were prepared by sol-gel method. The structures and low-temperature electrical conduction properties of these samples were investigated using x-ray diffraction, infrared spectra and alternating current impedance spectroscopy. All samples crystallized in an orthorhombic perovskite structure. Structural refinements reveal that the lattice parameters increased, while the orthorhombility decreased with Mn substitution. Further investigation of infrared spectrum indicates that the stretching vibration bands of Co-O bonds shifted towards lower wavenumbers followed by an increase of the population of Co³⁺ ions with intermediate spin state. These variations led to a reduced bandwidth of e_g band which could be the dominant reason for the abrupt decrease of bulk semi-conduction and the increase of activation energies for small polaron hopping conduction in PrCo_1−xMn_xO₃.     

Effect of Sn doping on the structural,optical, electrical and anticancer properties of WO3 nanoplates

This report is on the synthesis of Sn doped WO₃ nanoplates by a facile co-precipitation method. Various characterization tools have been employed to study the effect of Sn doping on the structural, optical and dielectric properties of WO₃ nanoplates. The successful incorporation of dopant ions in the monoclinic structure of WO₃ has been verified by XRD, EDX, FTIR and Raman spectroscopy. It has been observed that there is a broadening in optical band gap for doped samples due to the band filling effects caused by the crystal defects. Furthermore, the frequency dependent electrical properties of WO₃ nanoplates are found to be significantly tuned by Sn doping. Most importantly, this is one of the initial reports that Sn doped WO₃ nanoplates are an excellent candidate for anticancer applications. The anticancer activity of WO₃ nanoplates against MCF-7 cancer cells is increased with Sn doping which is attributed to several factors such as particle size, defects density and reactive oxygen species (ROS) production.     

Shape controlled synthesis of Cu3BiS3 nano- and microstructures by PEG assisted solvothermal method and functional properties

One-dimensional Cu₃BiS₃ nano-and microstructures were synthesized by solvothermal route using structural directing agent polyethylene glycol (PEG) as soft template. The effects of thiourea concentration on the morphological, structural and optical properties of Cu₃BiS₃ nano- and microstructures were investigated. X-ray diffraction study revealed that the synthesized Cu₃BiS₃ belongs to orthorhombic structure. Raman spectrum of the Cu₃BiS₃ exhibited its functional groups. The chemical bonding of the ions was examined by X-ray photoelectron spectroscopy. Field emission scanning electron microscope and transmission electron microscope analyses evidently showed that thiourea concentration acts as a crucial factor in tuning the morphology of Cu₃BiS₃ nano- and microstructures. The presence of Cu₃BiS₃ was confirmed by Energy Dispersive X-ray Analysis and elemental mapping. The growth mechanism of Cu₃BiS₃ nanostructures has been discussed. Conductivity of Cu₃BiS₃ measured by I-V characteristics of the nano- and microstructured film of ~ 2.5?µm thickness deposited on FTO substrate using electron beam evaporation method showed linear curve. The Hall measurements of the Cu₃BiS₃ films deposited on glass substrate were determined.     

Effect of Gd doping on structural,optical properties,photoluminescence and electrical characteristics of CdS nanoparticles for optoelectronics

Synthesis of pure and 0.1 to 5?wt.% Gd-doped CdS nanoparticles (NPs) was achieved through a modified domestic microwave-assisted route in a short timespan at 700?W power. The formation of hexagonal CdS NPs was verified via X-ray diffraction analysis, and no structural variation was observed except for lattice variation. The size of the crystallites (D), dislocation concentration, and lattice strain were calculated, and the D was in the range of 3–6?nm. Fourier transform-Raman analysis confirmed the presence of 1LO, 2LO, and 3LO modes at 294.76, 590, and 890?cm^?1, respectively, in all the synthesized nanostructures, with minute variations in their positions due to doping; however, no new mode was observed. The position of the vibration modes was red shifted compared to that of the bulk material, indicating a confinement effect. Scanning electron microscopy (SEM) mapping/energy-dispersive X-ray spectroscopy revealed homogeneous doping of Gd and the presence of all the constituents in the final products. The morphology of the synthesized materials was tested via field-emission SEM, which revealed spherical NPs with small dimensions. Additionally, high-resolution transmission electron microscopy was performed to visualize the shape and size of the prepared 0.1% Gd:CdS NPs. The energy gap was calculated using the Kubelka–Munk theory and found to be in the range of 2.31–2.41?eV. The photoluminescence emission spectra exhibited two green emission peaks at 516?±?2?nm and 555?±?2?nm and showed the reduction of defects with Gd doping in terms of intensity quenching. The dielectric constant (${\epsilon }^{\text{'}}$), loss, and alternating-current electrical properties were studied in the high-frequency range. The values of ${\epsilon }^{\text{'}}$ were in the range of 17–27. An enhancement of these values was observed for CdS when it was doped with Gd. The electrical conductivity exhibited frequency power law behavior.     

Sintering behavior,structure, and microwave properties of novel Li2xCu1-xMoO4 ceramics

In this study, we prepared a novel series of Li_2xCu_1-xMoO₄ (x = 0.02, 0.04, 0.06, 0.08, and 0.10) microwave ceramics. The dynamic sintering behavior, crystal phases, micro-morphologies, and dielectric properties of the samples were studied. The substitution of Li⁺ contributed to refining the crystal grain size, promoting the densification of microstructure, and enhancing the quality factor. Due to different valence substitutions, Cu⁺ ions were created, which were verified by X-ray photoelectron spectroscopy (XPS) and Raman experiments. In addition, the Raman shift, full width at half maximum (FWHM) value of the A_1g peak, and crystal microstrains were analyzed to gain a mechanistic understanding of the influence of structure on the dielectric properties. When x = 0.08, the Li_2xCu_1-xMoO₄ ceramic sintered at 675 °C exhibited optimal comprehensive properties with ε_r = 8.17, Qf = 68 476 GHz, and τ_f = ?25 ppm/°C, and good chemical stability between the ceramic and Al electrode was also achieved. These promising properties make Li_2xCu_1-xMoO₄ (x = 0.08) more suitable for ultra-low temperature co-fired ceramic (ULTCC) applications.     

Effect of Ca2+ site substitution on structural,optical, electrical and magnetic properties in Nd3+ and Mn2+-co-doped calcium molybdato-tungstates

Ca_1-3x-yMn_y[]_xNd_2x(MoO₄)_1-3x(WO₄)_3x molybdato-tungstates (? denotes vacant sites) were successfully synthesized by high-temperature solid-state reaction. New materials crystallize in scheelite-type structure within whole homogeneity range of solid solution (x ≤ 0.2000 and y = 0.0200). Morphological features and particle size distribution were investigated by SEM and laser diffraction methods, respectively. Spectroscopic measurements in the UV–vis range was carried out to determine optical direct band gap (E_g), Urbach energy (E_U) and confirmation of structural disorder. Refractive index (n) was calculated using four different models. Magnetic studies revealed paramagnetic behavior with long-range ferrimagnetic and short-range antiferromagnetic interactions. New materials showed weak n-type electrical conductivity and thermoelectric power factor (S²σ) that strongly depends on Nd³⁺ ions content. Dielectric parameters, i.e. relative permittivity (ε_r) and energy loss (tanδ) are insignificantly dependent on Nd³⁺ ions concentration. These effects were considered in terms of structural defects, thermal activation of charge carriers, and the Maxwell–Wagner polarization.     

Influence of silicon doping on the nanomorphology and surface chemistry of a wood-based carbon molecular sieve

Carbon–silica molecular sieves were prepared by carbonization of Scotch fir (Pinus sylvestris) after impregnation with aqueous waterglass (Na_xSi_yO_z, where x, y and z may take a range of values). Compared to Si-free samples, doping significantly modifies the structure that forms during the carbonization process. For carbonization temperatures between 600 °C and 1000 °C, doped samples shrink less than undoped samples, indicating increased mechanical strength. The specific surface area and pore volume develop in a combined self-activation and chemical vapour deposition (CVD) process. Nevertheless, the presence of the sodium silicates limits self-activation and thus reduces the porosity. Doping drastically reduces the specific surface area, measured both by gas adsorption and small angle X-ray scattering. The latter technique demonstrates that in both doped and undoped samples the specific surface area is isotropic. X-ray photoelectron spectroscopy (XPS) reveals that the spatial distribution of Na and Si atoms within the samples are not identical. The open honeycomb structure, conserved during the heat treatment from the original wood, provides easy access for gas adsorption and separation applications. The ratios of the microporous diffusion time constants of N₂ and O₂ from frequency response (FR) measurements gave separation factors 3.0, 4.3, 2.7 and 1.3 for samples prepared at 600 °C, 700 °C, 800 °C and 900 °C, respectively.     

Evolution of TiOx-SiOx nano-composite during annealing of ultrathin titanium oxide films on Si substrate

This paper discusses the formation of the TiO_x-SiO_x nano-composite phase during annealing of ultrathin titanium oxide films (~27 nm). The amorphous titanium oxide films are deposited on silicon substrates by sputtering. These films are important for high-k dielectrics and sensing applications. Annealing of these films at 750 °C in the O₂ environment (for 15–60 min) resulted in the polycrystalline rutile phase. The films exhibit Raman peaks at 150 cm⁻¹ (B_1g), 435 cm⁻¹ (E_g), and 615 cm⁻¹ (A_1g) confirming the rutile phase. The signature TO (1078 cm⁻¹) and LO (1259 cm⁻¹) infrared active vibrational modes of Si–O–Si bond confirms the presence of silicon-oxide. The X-ray photoelectron spectra of the TiO_x films show multiple peaks corresponding to Ti metal (453.8 eV); Ti⁴⁺ state (458.3 eV (Ti 2p_3/2) and 464 eV (Ti 2p_1/2)); and Ti³⁺ state (456.4 eV (Ti 2p_3/2) and 460.8 eV (Ti 2p_1/2)). The O1s XPS spectra peaks at 530–533 eV can be attributed to Ti–O and Si–O bonds of the TiO_x-SiO_x nano-composite phase in the annealed films. The depth profiling XPS study shows that the top surface of the annealed film is mainly TiO_x and the amount of SiO_x increases with the depth.     

Influence of Y doping on structural,vibrational, optical and magnetic properties of BiFeO3 ceramics prepared by Mechanical Activation

Y substituted BiFeO₃ (Bi_1−xY_xFeO_3; x=0.0–0.1) polycrystalline ceramics were synthesized by Mechanical Activation. The effect of varying composition of Y substitution on the structural, vibrational, optical and magnetic properties of doped BiFeO₃ (BFO) ceramics has been investigated. Rietveld refinement of X-ray diffraction patterns reveals that all samples crystallize in distorted rhombohedral structure with R3c symmetry and no structural transition has been observed. Raman spectroscopy also confirmed the distorted perovskite structure with R3c space group. Optical studies in the spectral range 1–4.5 eV were dominated by two d-d and three charge transfer (C-T) transitions. The optical band gap decreases from 2.11 to 2.01 eV with increasing Y substitution. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization with increasing Y concentration. Mechanical activation leads to significantly altered magnetic properties, particularly in higher Y-doping samples. The Mössbauer spectra demonstrate the suppression of spiral spin modulation of the magnetic moments resulting in enhanced ferromagnetism with increasing doping concentration. Significant increase in Néel temperature T_N in the substituted compounds was discussed on the basis of structural distortions.     

Mono and co-substitution of Sr2+ and Ca2+ on the structural,electrical and optical properties of barium titanate ceramics

In this work, Ba_0.9Sr_0.1TiO₃, Ba_0.7Sr_0.3TiO₃, Ba_0.5Sr_0.5TiO₃, Ba_0.5Ca_0.25Sr_0.25TiO₃ and Ba_0.5Ca_0.5TiO₃ have been synthesized to evaluate the influence of mono and co-substitution of A-site dopants (Sr²⁺ and Ca²⁺) on the structural, electrical and optical properties of BaTiO₃ ceramics. Sr²⁺ added samples showed a tetragonal structure which became slightly distorted with increasing Sr²⁺ concentration and finally achieved a cubic structure for x?=?0.50. Ba_0.5Ca_0.5TiO₃ also retained their tetragonality with limited solubility. Presence of second phase, CaTiO₃ demonstrated the fact of restricted solubility. The concurrent effect of Sr²⁺ and Ca²⁺ didn't alter the tetragonal structure. Sr²⁺ substitution enhanced the apparent density as well as grain size which stimulated the domain wall motion and improved dielectric properties. However, the ferroelectric nature of Ba_1-xSr_xTiO₃ was poor due to the redistribution of point defect at grain boundary. The optical band gap was found to be reduced from 3.48?eV to 3.28?eV with increasing Sr²⁺ content. Co-substitution of cations improved the electrical property significantly. The highest value of dielectric constant was found to be ～547 for Ba_0.5Ca_0.25Sr_0.25TiO₃ ceramics. Both Ba_0.5Ca_0.25Sr_0.25TiO₃ and Ba_0.5Ca_0.5TiO₃ had developed P-E loop having lower coercive field and moderate optical band gap energy. Co-doping with Sr²⁺ and Ca²⁺ was a good approach enhancing materials electrical as well as optical property.     

Structural and electrical properties of Dy3+ substituted NiFe2O4 ceramics prepared from powders derived by combustion method

Dysprosium (Dy) substituted nickel ferrite (NiDy_xFe_2-xO₄) powders with varying Dy content (x=0.0, 0.025, 0.05, 0.075, 0.1, 0.2) have been prepared by combustion method using DL-alanine fuel. Sintering characteristics of the powders and electrical properties of ceramics have been studied. Effective substitution of Dy³⁺ for Fe³⁺ is seen up to x=0.075 yielding improved properties, and a higher Dy content (x≥0.1) leads to partial substitution, disturbed stoichiometry, and diffusion of Dy to the grain boundaries and segregation as a secondary phase. Increasing Dy content reduces the crystallite size, powder particle size, and grain size in sintered ceramics, and the changing microstructural evolution is better resolved with back scattered electron imaging and compositional analysis. Raman spectroscopy confirms inverse spinel structure formation and substantiates the presence of secondary phase evidenced through X-ray diffraction and electron microscopy. A marginal increase in the electrical resistivity (ρ_dc) and magnetization are observed due to effectual substitution of Dy³⁺ for Fe³⁺ at the octahedral sites up to x=0.075. For x≥0.1, the increasing influence of highly resistive DyFeO₃ secondary phase at the inter-granular boundaries leads to a rapid increase in resistivity and reduction in dielectric losses, and the magnetization is reduced due to the anti-ferromagnetic nature of the secondary phase (DyFeO₃). Dense ceramics with high resistivity (~10⁹ Ω cm), low dielectric loss (tan δ ~0.002) at 1 MHz, and high magnetization (50.07 emu/g) are obtained for an optimum Dy content of x=0.075. Dielectric response, complex impedance, and electrical modulus spectroscopy in the frequency range (10⁻²–10⁶ Hz) reflect the changes in the microstructure, and suggests a non-Debye type relaxation.     

Modulation of electrical properties in single-walled carbon nanotube/conducting polymer composites

The preparation and electrical characterization of a new class of composite layers formed by dispersing single-walled carbon nanotubes (SWNT) in 1,8-diaminonaphthalene polymer, the poly(1,8-DAN), are described.The material was grown on the surface of Pt plates by electropolymerization of 1,8-diaminonaphthalene (1,8-DAN) monomer in the presence of nanotubes. This synthesis method allows the simultaneous deposition of both the host polymer matrix and the filler nanotubes. A series of composite films were prepared using untreated nanotubes as well as nanotubes treated with KOH, HNO₃ and HNO₃/H₂SO₄ solutions. The structural features of the nanotubes and of the films produced have been investigated using Raman spectroscopy. Insight into the nature of nanotube dispersion and nanotube-polymer association was gained by AFM and STM analysis and by FE-SEM inspection after removing the outermost portion of composite films.The charge transport in composite films is found to be strongly enhanced by the nanotube insertion. Depending on the SWNTs processing, currents up to 30 mA, higher by a factor of about 140 than those of the pure poly(1,8-DAN) films, were measured with an applied voltage of 250 mV.     

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.     

Influence of surface properties of carbon fibres on the adsorption of catalase

PAN-based carbon fibres obtained by carbonisation at relatively low temperature and submitted to high-temperature treatment and oxidation in wet conditions provided a range of materials differing according to surface composition and hydrophobicity. The adsorption of catalase by these fibres was studied by XPS and by activity measurements in the liquid and in the adsorbed state. Three typical situations are featured: limited adsorbed amount in the case of low hydrophobicity; significant adsorption and preservation of an appreciable enzyme activity for samples of moderate hydrophobicity; strong adsorption with deactivation of the enzyme in the case of high hydrophobicity.     

Influence of Mg doping on the structural,optical, and electrical properties of Zn0.95Li0.05O Nanoparticles

This study investigates the effect of Li and Mg codoping on the structural, optical, and electrical properties of the ZnO. Zn_0.95−xLi_0.05Mg_xO (x = 0.00, 0.01, 0.02, 0.03) nanoparticles are synthesized by hydrothermal method. X-ray diffraction (XRD) results confirmed that all samples are polycrystalline with a hexagonal-wurtzite structure. The surface morphology of the samples were examined by Scanning Electron Microscopy (SEM). The SEM analysis showed that all samples exhibit cheese-like plates and the plate sizes increase with Mg addition. Optical properties were examined by UV-VIS diffuse reflectance spectroscopy. The optical measurements indicate that the reflectance edge of the samples have red shift up to 2% Mg doping level, but blue-shift for 3% Mg doping. The optical band gap of Zn_0.95−xLi_0.05Mg_xO nanostructures are calculated as 3.227, 3.214, 3.209, and 3.221 eV with x = 0.00, 0.01, 0.02, 0.03 respectively. Electrical properties including the carrier concentration, Hall mobility, and resistivity were studied using Van-der Pauw method. The temperature resistivity curves of the samples shown typical semiconductor behavior. The carrier concentration decreases with increasing doping level up to 2% Mg, and it slightly increases for 3% Mg. The variation of the Hall mobility for the samples is inversely proportional to the carrier concentration.     

Field emission properties of N2 and Ar plasma-treated multi-wall carbon nanotubes

We modify multi-wall carbon nanotubes (MWCNTs) by plasma treatment with N₂ and Ar for varying durations and measure their field emission characteristics. The N₂ treated MWCNTs showed significant improvement in field emission properties, while the Ar treated MWCNTs displayed poorer field emission characteristics compared to untreated MWCNTs. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman spectroscopy and work function measurements are used to investigate the field emission mechanisms after plasma treatments.     

Carbon/carbon composites derived from poly(ethylene oxide)‐modified novolac‐type phenolic resin: Microstructure and physical,and morphological properties

A poly(ethylene oxide) (PEO) novolac‐type phenolic resin blend was prepared by the physical blending method. The modified novolac‐type phenolic resin with various PEO contents was used as a matrix precursor to fabricate carbon/carbon composites. The effect of the PEO/phenolic resin mixing ratio on the change of the density and of the porosity was studied. The flexural strength and interlaminar shear strength of the PEO/phenolic resin blend‐derived carbon/carbon composites were also investigated. The results show that the density of the PEO/phenolic resin blend‐derived carbon/carbon composites decreases with the PEO content. The X‐ray diffraction and Raman spectra studies showed that the carbon fiber in the samples will affect the growth of the ordered carbon structure. From SEM morphological observation, it is shown that the fracture surface of specimens is smooth. Also, there is less fiber pull‐out and fiber breakage on the fracture surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1609–1619, 2002; DOI 10.1002/app.10407