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Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

Volume 33 (2015): Issue 1 (March 2015)

Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

30 Articles
Open Access

Two-phase synthesis of olive-like NiS particles and chain-like Bi2S3 nanowires

Published Online: 13 Mar 2015
Page range: 1 - 5

Abstract

Abstract

Highly dispersed olive-like NiS particles were synthesized in a liquid-liquid biphasic system at room temperature, where nickel xanthate in organic solvents (toluene and benzene) and sodium sulfide in water solution were used as nickel and sulfide sources, respectively. NiS particles were formed at the stabilized phase interface. The structures, chemical composition and optical characteristics of the products were investigated by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The organic solvents obviously influenced the morphology of the NiS particles. The olive-like NiS with smooth surface and sharp ends was obtained at benzene/water interface, while spindle-like NiS particles with rough surface and circle ends were formed when using toluene as a solvent. Analogously, chainlike Bi2S3 nanowires were produced at chloroform/water interface. The effect of the experiment parameters including reaction time, solvent and concentration of reactants on the size and morphology of the products was discussed in detail and a possible formation mechanism was suggested.

Keywords

  • two-phase method
  • crystal morphology
  • nanomaterials
  • semiconducting materials
Open Access

Antireflective bilayer coatings based on Al2O3 film for UV region

Published Online: 13 Mar 2015
Page range: 6 - 10

Abstract

Abstract

Bilayer antireflective coatings consisting of aluminium oxide Al2O3/MgF2 and Al2O3/SiO2 are presented in this paper. Oxide films were deposited by means of e-gun evaporation in vacuum of 5 × 10-3 Pa in the presence of oxygen, and magnesium fluoride was prepared by thermal evaporation on heated optical lenses made from quartz glass (Corning HPFS). Substrate temperature was maintained at 250 _C during the deposition. Thickness and deposition rate were controlled with a thickness measuring system Inficon XTC/2. The experimental results of the optical measurements carried out during and after the deposition process have been presented. Physical thickness measurements were made during the deposition process and resulted in 44 nm/52 nm for Al2O3/MgF2 and 44 nm/50 nm for Al2O3/SiO2 system. Optimization was carried out for ultraviolet region with minimum of reflectance at 300 nm. The influence of post deposition annealing on the crystal structure was determined by X-ray measurements. In the range from ultraviolet to the beginning of visible region, the reflectance of both systems decreased and reached minimum at 290 nm. The value of reflectance at this point, for the coating Al2O3/MgF2 was equal to R290nm = 0.6 % and for Al2O3/SiO2R290nm = 1.1 %. Despite the difference between these values both are sufficient for applications in the UV optical systems for medicine and UV laser technology.

Keywords

  • Al2O3/MgF2
  • Al2O3/SiO2
  • antireflective coatings
  • optical properties
Open Access

Influence of uniaxial stresses on electronic and optical properties of β-K2SO4 crystal

Published Online: 13 Mar 2015
Page range: 11 - 17

Abstract

Abstract

In view of possible practical applications of transparent crystals for mechanical stress sensors, theoretical investigation of piezo(elasto)optic effect in crystals might be useful for searching for proper materials, possessing large coefficients of elasto-optic effect, and for determination of uniaxial stress directions of maximum piezo-optical sensitivity. The influence of the uniaxial stresses on the electronic band structure, density of states, and optical properties of potassium sulphate crystal β-K2SO4 have been studied in the framework of the density functional theory using the ab initio CASTEP code. Increase in the band gap, Eg of the crystal takes place for three crystallographic directions and for moderate uniaxial stresses, σ < 1.5 GPa. Dependencies of principal refractive indices and polarizabilities upon principal uniaxial stresses are discussed together with other features of electronic structure of the crystal.

Keywords

  • crystals
  • insulators
  • electronic band structure
  • uniaxial stress
  • refractive indices
Open Access

Rietveld refinement on XRD and TEM study of nanocrystalline PbZr0:5Ti0:5O3 ceramics prepared with a soft chemistry route

Published Online: 13 Mar 2015
Page range: 18 - 24

Abstract

Abstract

PbZr0:5Ti0:5O3 nanopowders (~27 nm) have been prepared by a controlled reconstructive thermal decomposition and crystallization from an amorphous polymeric precursor with polyvinyl alcohol (PVA) and sucrose at 400 to 700 °C in air. The Rietveld refinement of the XRD profiles which were recorded at room temperature for the PbZr0:5Ti0:5O3 powder prepared by a thermal treatment at 700 °C for 2 h, confirmed the P4mm tetragonal crystal structure of the as prepared PbZr0:5Ti0:5O3 nanopowders, with a = 0.4036 nm and c = 0.4147 nm. A hexagonal symmetry (R3c), with a = 0.5774 nm and c = 1.4212 nm, was also detected from Rietveld refinement analysis. Thus, tetragonal and hexagonal phases were found to coexist with the as prepared PbZr0:5Ti0:5O3 nanopowders. The average particle size (D) of the PbZr0:5Ti0:5O3 powders, estimated with the help of the specific surface area, measured by BET method, was 26.1 nm. Average D value, calculated by D2θ1/2 in the XRD peaks with the Debye-Scherrer relation was ~24 nm. TEM study made it possible to measure the particle size of PbZr0:5Ti0:5O3 powders with an average diameter of 27 nm.

Keywords

  • precursor method
  • PbZr0:5Ti0:5O3 nanopowders
  • tetragonal phase
  • PVA-sucrose
  • ferroelectrics
Open Access

Electrochemical behavior and conductivity measurements of electropolymerized selenophene-based copolymers

Published Online: 13 Mar 2015
Page range: 25 - 35

Abstract

Abstract

Electrochemical copolymerization of selenophene and thiophene was performed at a constant electrode potential. The obtained homopolymer films and copolymers were studied and characterized with cyclic voltammetry and conductivity measurements, from which conductivity values around 13.35 S · cm-1 were determined. The influence of the applied electropolymerization potential and the monomer feed ratio of selenophene and thiophene on the copolymers properties was investigated. The obtained copolymers showed good stability of the redox activity in an acetonitrile-based electrolyte solution. At higher polymerization potentials and at higher concentrations of thiophene in the feed, more thiophene units were incorporated into the copolymer chain. The conductivities of the copolymers were between those of homopolymers, implying that oxidation of both monomers was possible and the copolymer chains might accordingly be composed of both selenophene and thiophene units.

Keywords

  • electropolymerization
  • intrinsically conducting polymers
  • polythiophene
  • polyselenophene
Open Access

Influence of duration time of CVD process on emissive properties of carbon nanotubes films

Published Online: 13 Mar 2015
Page range: 36 - 46

Abstract

Abstract

In this paper various types of films made of carbon nanotubes (CNTs) are presented. These films were prepared on different substrates (Al2O3, Si n-type) by the two-step method. The two-step method consists of physical vapor deposition step, followed by chemical vapor deposition step (PVD/CVD). Parameters of PVD process were the same for all initial films, while the duration times of the second step - the CVD process, were different (15, 30 min.). Prepared films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and field emission (FE) measurements. The I-E and F-N characteristics of electron emission were discussed in terms of various forms of CNT films. The value of threshold electric field ranged from few V/μm (for CNT dispersed rarely on the surface of the film deposited on Si) up to ~20 V/μm (for Al2O3 substrate).

Keywords

  • carbon nanotubes film
  • field emission
  • SEM
  • TEM
Open Access

Synthesis of SiO2 nanopowders containing quartz and cristobalite phases from silica sands

Published Online: 13 Mar 2015
Page range: 47 - 55

Abstract

Abstract

In this study, extraction and synthesis of SiO2 nanoparticles from silica sands have been conducted by means of two different methods, i.e. dry method (method 1) and hydrothermal process (method 2). The basic difference between the two methods is in the extraction step. The two methods were compared in terms of being more efficient, economical, and superior in obtaining SiO2 nanoparticles. The SiO2 nanoparticles were characterized in terms of phase purity, crystallinity, Si-O functional bonding as well as particles size and morphology. The most interesting fact in this study was the formation of both quartz and cristobalite phases within all prepared SiO2 nanoparticles.

Keywords

  • silica sand
  • SiO2 nanoparticles
  • quartz and cristobalite phases
Open Access

Hydrogen permeation properties of Pd-coated Pd33Ni52Si15 amorphous alloy membrane

Published Online: 13 Mar 2015
Page range: 56 - 58

Abstract

Abstract

The vast majority of experimental techniques used for the measurements of hydrogen permeability through metallic membranes whose one or both surfaces are covered with a thin Pd film is based on the assumption that a ratio of film-to-membrane thickness is small enough to cause hydrogen flow to be independent of the Pd film thickness. In an attempt to verify this assumption, we have measured the hydrogen flow through the Pd33Ni52Si15 amorphous membrane covered with Pd film of 10, 20, and 30 nm in thickness. Contrary to our expectations, we have found a dramatic decrease in hydrogen flow with the increase in Pd film thickness. Our findings are discussed in terms of potential barrier between the two different phases.

Keywords

  • permeability
  • hydrogen
  • palladium alloys
  • membrane
  • metallic glasses
Open Access

Green synthesis and characterization of Ag1/2Al1/2TiO3 nanoceramics

Published Online: 13 Mar 2015
Page range: 59 - 72

Abstract

Abstract

Single phase silver aluminum titanate (Ag1/2Al1/2)TiO3, later called AAT, nanoceramic powder (particle size 2 to 7.5 nm) was synthesized by a low-cost, green and reproducible tartaric acid gel process. X-ray, FT-IR, energy dispersive X-ray and high resolution transmission electron microscopy analyses were performed to ascertain the formation of AAT nanoceramics. X-ray diffraction data analysis indicated the formation of monoclinic structure having the space group P2/m(10). UV-Vis study revealed the surface plasmon resonance at 296 nm. Dielectric study revealed that AAT nanoceramics could be a suitable candidate for capacitor applications and meets the specifications for “Z7R” of Class I dielectrics of Electronic Industries Association. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were performed using the impedance data. Electric modulus studies supported the hopping type of conduction in AAT. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in AAT. The ac conductivity data were used to evaluate the density of states at Fermi level and minimum hopping length of the compound.

Keywords

  • electronic materials
  • oxides
  • chemical synthesis
  • dielectric properties
  • electrical properties
Open Access

Magnetoresistance peculiarities and magnetization of materials with two kinds of superconducting inclusions

Published Online: 13 Mar 2015
Page range: 73 - 81

Abstract

Abstract

Low-temperature properties of a crystal containing type I superconducting inclusions of two different materials have been studied. In the approximation assuming that the inclusions size is much smaller than the coherence length/penetration depth of the magnetic field, the theory of magnetoresistance of a crystal containing spherical superconducting inclusions of two different materials has been developed, and magnetization of crystals has been calculated. The obtained results can be used for correct explanation of the low temperature conductivity in binary and more complex semiconductors, in which precipitation of the superconducting phase is possible during the technological processing or under external impact.

Keywords

  • spherical superconducting inclusion
  • magnetoresistance
  • magnetization
  • type I superconductors
Open Access

Computer simulation of sputtering of graphite target in magnetron sputtering device with two zones of erosion

Published Online: 13 Mar 2015
Page range: 82 - 94

Abstract

Abstract

A computer simulation program for discharge in a magnetron sputtering device with two erosion zones was developed. Basic laws of the graphite target sputtering process and transport of sputtered material to the substrate were taken into account in the Monte Carlo code. The results of computer simulation for radial distributions of density and energy flux of carbon atoms on the substrate (at different values of discharge current and pressure of the working gas) confirmed the possibility of obtaining qualitative homogeneous films using this magnetron sputtering device. Also the discharge modes were determined for this magnetron sputtering device, in which it was possible to obtain such energy and density of carbon atoms fluxes, which were suitable for deposition of carbon films containing carbon nanotubes and other nanoparticles.

Keywords

  • Monte Carlo computer simulation
  • magnetron sputtering
  • flux of particles
  • carbon
  • graphite target
  • energy of particles
Open Access

Phase, microstructure and microwave dielectric properties of Mg0:95Ni0:05Ti0:98Zr0:02O3 ceramics

Published Online: 13 Mar 2015
Page range: 95 - 99

Abstract

Abstract

Mg0:95Ni0:05Ti0:98Zr0:02O3 ceramics was prepared via conventional solid-state mixed-oxide route. The phase, microstructure and microwave dielectric properties of the sintered samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and a vector network analyzer. The microstructure comprised of circular and elongated plate-like grains. The semi quantitative analysis (EDS) of the circular and elongated grains revealed the existence of Mg0:95Ni0:05T2O5 as a secondary phase along with the parent Mg0:95Ni0:05Ti0:98Zr0:02O3 phase, which was consistent with the XRD findings. In the present study, εr ~17.1, Qufo~195855 ± 2550 GHz and τf ~ -46 ppm/K was achieved for the synthesized Mg0:95Ni0:05Ti0:98Zr0:02O3 ceramics sintered at 1325 °C for 4 h.

Keywords

  • phase
  • microstructures
  • ceramics
Open Access

Influence of different synthesis conditions on properties of oleic acid-coated-Fe3O4 nanoparticles

Published Online: 13 Mar 2015
Page range: 100 - 106

Abstract

Abstract

In the present paper, iron oxide nanoparticles coated by oleic acid have been synthesized in different conditions by coprecipitation method. For investigating the effect of time spent on adding the oleic acid to the precursor solution, two different processes have been considered. The as synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Magnetic measurement was carried out at room temperature using a vibrating sample magnetometer (VSM). The results show that the magnetic nanoparticles decorated with oleic acid decreased the saturation of magnetization. From the data, it can also be concluded that the magnetization of Fe3O4/oleic acid nanoparticles depends on synthesis conditions.

Keywords

  • co-precipitation
  • super-paramagnetic nanoparticles
  • oleic acid
  • strain
  • magnetite
Open Access

Magnetoelectric effect in (BiFeO3)x–(BaTiO3)1-x solid solutions

Published Online: 13 Mar 2015
Page range: 107 - 112

Abstract

Abstract

The aim of the present work was to study magnetoelectric effect (ME) in (BiFeO3)x-(BaTiO3)1-x solid solutions in terms of technological conditions applied in the samples fabrication process. The rapidly growing interest in these materials is caused by their multiferroic behaviour, i.e. coexistence of both electric and magnetic ordering. It creates possibility for many innovative applications, e.g. in steering the magnetic memory by electric field and vice versa. The investigated samples of various chemical compositions (i.e. x = 0.7, 0.8 and 0.9) were prepared by the solid-state sintering method under three sets of technological conditions differing in the applied temperature and soaking time. Measurements of the magnetoelectric voltage coefficient αME were performed using a dynamic lock-in technique. The highest value of αME was observed for 0.7BiFeO3-0.3BaTiO3 solid solution sintered at the highest temperature (T = 1153 K) after initial electrical poling despite that the soaking time was reduced 10 times in this case.

Keywords

  • magnetoelectric effect
  • multiferroic materials
  • magnetoelectric voltage coefficient
Open Access

Reactive bay functionalized perylene monoimide-polyhedral oligomeric silsesquioxane organic electronic dye

Published Online: 13 Mar 2015
Page range: 113 - 121

Abstract

Abstract

Aggregation-induced quenching is particularly detrimental in perylene diimides, which are characterized by a near-unity fluorescence quantum yield in solution but are far less emissive in the solid state. Previously, perylene diimide has been improved by linking it to the inorganic cage of polyhedral oligomeric silsesquioxanes. As a further study on perylene diimidepolyhedral oligomeric silsesquioxanes, we report on a double functionalized molecular structure, which can be used for substitution at the bay area and as a side group in other materials. Typical solution absorption and emission features of the perylene diimide fragment have been observed in this new reactive perylene diimide-polyhedral oligomeric silsesquioxane. Moreover, reduced stacking during aggregation and spherical particles exhibiting solid fluorescence have been obtained. Organic semiconducting material with enhanced solid state photophysical properties, like solid fluorescence is a subject of great interest owing to its possible high-tech applications in optoelectronic devices.

Keywords

  • perylene diimides
  • polyhedral oligomeric silsesquioxane
  • fluorescence
  • optoelectronics
  • self assembly
Open Access

Analysis of emission of Eu3+ and Dy3+ doped Magnesium Boro-Tellurite (MBT) ceramics

Published Online: 13 Mar 2015
Page range: 122 - 125

Abstract

Abstract

Rare earth (RE) ions play an important role in the improvement of the optical properties of ceramics. Rare-earth ceramics are commonly used in display panels, fluorescent lamps and lasers. The luminescence properties of Magnesium Boro-Tellurite (MBT) Eu3+ and Dy3+ doped ceramics have not been reported before. Therefore, the aim of this paper is to determine the effect of different compositions on the luminescence properties of the MBT material. A series of xTeO2-(70-x)B2O3-30MgO ceramics with 10 ≤ x ≤ 40 mol % doped with 1 mol % of Eu3+ and Dy3+ ions was prepared via the solid-state reaction method. The influence of various compositions on the crystalline phase and photoluminescence properties of the samples were investigated by X-ray diffraction (XRD) and luminescence spectroscopy. The crystalline phases obtained in this study are Mg3(BO3)2, MgB4O7, Mg2B2O5, Mg(Te2O5) and MgTe3O6. It was stated that the crystalline phases have not changed as a result of doping with Eu3+ and Dy3+ ions. The emission spectra of Eu3+: MBT ceramics showed strong red emission at 612 nm due to the transition of 5D07F2 and meanwhile, the Dy3+: MBT ceramics showed a blue emission at 480 nm due to 4F9/2 6H15/2 transition and yellow emission at 576 nm due to 4F9/26H13/2 transition. Both the rare-earth doped phosphors showed bright emission.

Keywords

  • Magnesium Boro-Tellurite (MBT)
  • luminescence
  • ceramics
Open Access

Phase, microstructure and microwave dielectric properties of A-site deficient (La, Nd)2/3TiO3 perovskite ceramics

Published Online: 13 Mar 2015
Page range: 126 - 130

Abstract

Abstract

(La, Nd)2/3TiO3 ceramics were prepared through a conventional solid state mixed oxide route. For phase and microstructure analysis, XRD and SEM were used, respectively. Microwave dielectric properties were measured using a network analyzer. XRD patterns revealed the formation of the parent (La, Nd)2/3TiO3 phase along with (La, Nd)4Ti9O24 as a secondary phase. The microstructure consisted of rectangular and needle shaped grains, which decreased in size from 4 μm to 2 μm with an increase in sintering temperature from 1300 °C to 1350 °C. Decrease in grain size caused an increase in density of the samples from 4.81 g/cm3 to 5.17 g/cm3. Microwave dielectric properties of the samples calcined and sintered in air atmosphere were εr = 40.35, Q × f = 3499 GHz and τf = 0 ppm/°C, whereas for a sample calcined in nitrogen and sintered in air they were εr = 40.18, Q × f = 4077 GHz and τf = +4.9 ppm/°C, respectively.

Keywords

  • A-site deficient perovskites
  • dielectrics
  • phase analysis
  • ceramics
Open Access

Evaluation of the acid properties of aluminossilicate MCM-22 material synthesized under static conditions

Published Online: 13 Mar 2015
Page range: 131 - 136

Abstract

Abstract

The hydrothermal synthesis of MCM-22 zeolite was carried out using silica, sodium aluminate and hexamethyleneimine, under static conditions at 150 °C for a period of 10 days, followed by washing with deionized water, drying overnight and calcination at 650 °C. The obtained material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The XRD analysis evidenced that MCM-22 presented a well defined MWW structure. The FT-IR spectrum confirmed the efficiency of the hexamethyleneimine as an organic template used to direct the structure of the MCM-22 zeolite under static conditions. The SEM image indicated that the particles are spherical in shape, with a diameter of ca. 10 μm. The acid properties of the MCM-22 zeolite, as determined by n-buthylamine adsorption, were investigated in the temperature ranges of 105 to 300 °C and 300 to 525 °C, relative to medium and strong acid sites, respectively.

Keywords

  • crystal structure
  • synthesis of zeolites
  • porous materials
  • MCM-22
Open Access

Surface morphology of titanium nitride thin films synthesized by DC reactive magnetron sputtering

Published Online: 13 Mar 2015
Page range: 137 - 143

Abstract

Abstract

In this paper the influence of temperature on the 3-D surface morphology of titanium nitride (TiN) thin films synthesized by DC reactive magnetron sputtering has been analyzed. The 3-D morphology variation of TiN thin films grown on p-type Si (100) wafers was investigated at four different deposition temperatures (473 K, 573 K, 673 K, 773 K) in order to evaluate the relation among the 3-D micro-textured surfaces. The 3-D surface morphology of TiN thin films was characterized by means of atomic force microscopy (AFM) and fractal analysis applied to the AFM data. The 3-D surface morphology revealed the fractal geometry of TiN thin films at nanometer scale. The global scale properties of 3-D surface geometry were quantitatively estimated using the fractal dimensions D, determined by the morphological envelopes method. The fractal dimension D increased with the substrate temperature variation from 2.36 (at 473 K) to 2.66 (at 673 K) and then decreased to 2.33 (at 773 K). The fractal analysis in correlation with the averaged power spectral density (surface) yielded better quantitative results of morphological changes in the TiN thin films caused by substrate temperature variations, which were more precise, detailed, coherent and reproducible. It can be inferred that fractal analysis can be easily applied for the investigation of morphology evolution of different film/substrate interface phases obtained using different thin-film technologies.

Keywords

  • atomic force microscopy (AFM)
  • DC reactive magnetron sputtering
  • fractal analysis
  • surface roughness
  • titanium nitride (TiN) thin film
Open Access

Infrared luminescence and thermoluminescence of lithium borate glasses doped with Sm3+ ions

Published Online: 13 Mar 2015
Page range: 144 - 151

Abstract

Abstract

Thermoluminescence (TL) characteristics of X-ray irradiated pure and doped with Sm3+ ions Li2O-MO-B2O3 (where MO=ZnO, CaO, CdO) glasses have been studied in the temperature range of 303 to 573 K. All the pure glasses exhibited single TL peaks at 382 K, 424 K and 466 K. When these glasses were doped with Sm3+ ions no additional peaks have been observed but the glow peak temperature of the existing glow peak shifted gradually towards higher temperatures with gain in intensity of TL light output. The area under the glow curve was found to be maximum for Sm3+ doped glasses mixed with cadmium oxide as a modifier. The trap depth parameters associated with the observed TL peaks have been evaluated using Chen’s formulae. The possible use of these glasses in radiation dosimetry has been described. The results clearly showed that samarium doped cadmium borate glass has a potential to be considered as a thermoluminescence dosimeter.

Keywords

  • infrared spectra
  • thermoluminescence
  • borate glasses
  • samarium ions
Open Access

High temperature thermoelectric properties of PbTe prepared by high pressure method

Published Online: 13 Mar 2015
Page range: 152 - 156

Abstract

Abstract

Highly dispersed olive-like NiS particles were synthesized in a liquid-liquid biphasic system at room temperature, where nickel xanthate in organic solvents (toluene and benzene) and sodium sulfide in water solution were used as nickel and sulfide sources, respectively. NiS particles were formed at the stabilized phase interface. The structures, chemical composition and optical characteristics of the products were investigated by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The organic solvents obviously influenced the morphology of the NiS particles. The olive-like NiS with smooth surface and sharp ends was obtained at benzene/water interface, while spindle-like NiS particles with rough surface and circle ends were formed when using toluene as a solvent. Analogously, chainlike Bi2S3 nanowires were produced at chloroform/water interface. The effect of the experiment parameters including reaction time, solvent and concentration of reactants on the size and morphology of the products was discussed in detail and a possible formation mechanism was suggested.

Keywords

  • thermoelectric material
  • high pressure
  • PbTe
Open Access

Effect of fabrication technique on the crystalline phase and electrical properties of PVDF films

Published Online: 13 Mar 2015
Page range: 157 - 162

Abstract

Abstract

The effect of different fabrication techniques on the formation of electroactive β-phase polyvinylidene fluoride (PVDF) has been investigated. Films with varying concentration of PVDF and solvent - dimethyl formamide (DMF) were synthesized by tape casting and solvent casting techniques. The piezoelectric β-phase as well as non polar β-phase were observed for both the tape cast and solvent cast films from X-ray diffraction (XRD) micrographs and Fourier transform infra-red spectroscopy (FT-IR) spectra. A maximum percentage (80 %) of β-phase was obtained from FT-IR analysis for a solvent cast PVDF film. The surface morphology of the PVDF films was analyzed by FESEM imaging. The dielectric properties as a function of temperature and frequency and the ferroelectric hysteresis loop as a function of voltage were measured. An enhancement in the value of the dielectric constant and polarization was obtained in solvent cast films.

Keywords

  • PVDF
  • crystallinity
  • dielectric
  • remanent polarization
Open Access

Nanosized MoO3 as a reusable heterogeneous catalyst for the synthesis of 2,6-bis(benzylidene)cyclohexanones

Published Online: 13 Mar 2015
Page range: 163 - 168

Abstract

Abstract

Crystalline MoO3 nanoparticles were obtained by electrochemical synthesis process using tetrapropylammonium bromide as a stabilizer and structure-directing agent in ACN:THF(4:1) solvent. Formation of MoO3 nanoparticles took place at a constant supply current of 14 mA/cm2. These synthesized MoO3 nanoparticles were characterized by UV-Vis spectroscopy, FT-IR spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM). So prepared MoO3 nanoparticles were used as a heterogeneous catalyst for the synthesis of 2,6-bis(benzylidene)cyclohexanone derivatives. This protocol offers several advantages, such as simple work-up procedure, recyclability of the catalyst, excellent product yield in a short reaction time and purification of products with a non-chromatographic method.

Keywords

  • electrochemical synthesis
  • MoO3 nanoparticles
  • heterogeneous catalyst
  • 2,6-bis(benzylidene)cyclohexanone
Open Access

First principles study of structure, electronic and optical properties of Y3Fe5O12 in cubic and trigonal phases

Published Online: 13 Mar 2015
Page range: 169 - 174

Abstract

Abstract

First principles calculations have been performed to investigate the structure, electronic and optical properties of Y3Fe5O12. Both the cubic and trigonal phases have been considered in our calculation. The calculated structural parameters are slightly larger than the experimental values. The band structures show that Y3Fe5O12 in cubic and trigonal phases have direct band gaps of 0.65 and 0.17 eV. The calculations of dielectric function, absorption, extinction coefficient, refractive index, energy loss function and reflectivity are presented.

Keywords

  • Y3Fe5O12
  • first principles
  • electronic structure
  • optical properties
Open Access

Morphological features in aluminum nitride epilayers prepared by magnetron sputtering

Published Online: 13 Mar 2015
Page range: 175 - 184

Abstract

Abstract

The aim of this study is to characterize the surface topography of aluminum nitride (AlN) epilayers prepared by magnetron sputtering using the surface statistical parameters, according to ISO 25178-2:2012. To understand the effect of temperature on the epilayer structure, the surface topography was investigated through atomic force microscopy (AFM). AFM data and analysis of surface statistical parameters indicated the dependence of morphology of the epilayers on their growth conditions. The surface statistical parameters provide important information about surface texture and are useful for manufacturers in developing AlN thin films with improved surface characteristics. These results are also important for understanding the nanoscale phenomena at the contacts between rough surfaces, such as the area of contact, the interfacial separation, and the adhesive and frictional properties.

Keywords

  • aluminum nitride epilayer
  • atomic force microscopy
  • magnetron sputtering
  • substrate
  • surface roughness
Open Access

Synthesis, characterization and fabrication of copper nanoparticles in N-isopropylacrylamide based co-polymer microgels for degradation of p-nitrophenol

Published Online: 13 Mar 2015
Page range: 185 - 192

Abstract

Abstract

Poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAM-co-AAc)] microgels were synthesized by precipitation polymerization. Copper nanoparticles were successfully fabricated inside the microgels by in-situ reduction of copper ions in an aqueous medium. The microgels were characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and Dynamic Light Scattering (DLS). Hydrodynamic radius of P(NIPAM-co-AAc) microgel particles increased with an increase in pH in aqueous medium at 25 °C. Copper-poly(N-isopropylacrylamide-co-acrylic acid) [Cu-P(NIPAM-co-AAc)] hybrid microgels were used as a catalyst for the reduction of 4-nitrophenol (4-NP). Effect of temperature, concentration of sodium borohydride (NaBH4) and catalyst dosage on the value of apparent rate constant (kapp) for catalytic reduction of 4-NP in the presence of Cu-P(NIPAM-co-AAc) hybrid microgels were investigated by UV-Vis spectrophotometry. It was found that the value of kapp for catalytic reduction of 4-NP in the presence of Cu-P(NIPAM-co-AAc) hybrid microgel catalyst increased with an increase in catalyst dosage, temperature and concentration of NaBH4 in aqueous medium. The results were discussed in terms of diffusion of reactants towards catalyst surface and swelling-deswelling of hybrid microgels.

Keywords

  • microgels
  • copper
  • nitrophenol
  • catalysis
  • energy of activation
Open Access

Synthesis of polyaniline nanotubes through UV light catalytic method

Published Online: 13 Mar 2015
Page range: 193 - 197

Abstract

Abstract

In this study, nitrocellulose (NC) fiber blanket prepared by electrostatic spinning method has been used as a template, and copper nitrate (Cu(NO3)2) as an oxidant to synthesise polyaniline nanotubes doped with heteropolyacid (H4SiW12O40, SiW12) using UV light catalytic method. Infrared spectroscopy (IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) technologies were applied to characterize the prepared samples of polyaniline nanotubes. The results show that the external diameter of the tube is about 200 nm, and the internal diameter about 170 nm. We also give a reasonable speculation and explanation about the formation mechanism of the nanotubes.

Keywords

  • UV irradiation
  • polyaniline
  • nanotubes
  • template
  • heteropolyacid
Open Access

Influence of aluminium concentration in Zn0:9V0:1O nanoparticles on structural and optical properties

Published Online: 13 Mar 2015
Page range: 198 - 204

Abstract

Abstract

The (V,Al) co-doped ZnO nano-structured powders (Zn0.9-xV0.1AlxO, where x = 0.02, 0.03 and 0.04) were synthesized via the sol-gel technique and their structural and optical properties were investigated. The effect of Al concentration on the structural and optical properties of the Zn0.9-xV0.1AlxO nanopowders was studied using various techniques. The XRD patterns indicate that the samples have a polycrystalline wurtzite structure. The crystallite size increases with increasing the Al content and lies in the range of 23 to 30 nm. The lattice strain, estimated by the Stokes-Wilson equation, decreases when Al content increases. SEM and TEM micrographs show that Zn0.9-xV0.1AlxO powders are the agglomeration of nanoparticles having spherical and hexagonal shapes with dimensions ranging from 20 to 30 nm. FT-IR spectra show a distinct absorption peak at about 500 cm-1 for ZnO stretching modes and other peaks related to OH and H2O bands. Raman spectra confirm the wurtzite structure of the Zn0.9-xV0.1AlxO nanoparticles. The direct band gaps of the synthesized Zn0.9-xV0.1AlxO nanopowders, estimated from the Brus equation and the crystallite sizes deduced from XRD, are around 3.308 eV. The decomposition process of the dried gel system was investigated by thermal gravimetric analysis (TGA).

Keywords

  • ZnO nanopowder
  • V and Al co-doping
  • XRD
  • TEM
  • Raman scattering
Open Access

Investigation on room temperature photoluminescence of pure and aluminum doped zinc oxide nanoparticles

Published Online: 13 Mar 2015
Page range: 205 - 212

Abstract

Abstract

Pure and aluminum doped zinc oxide nanoparticles were prepared by soft chemical method. The prepared nanoparticles were characterized by XRD, SEM-EDAX, UV-Vis, PL and FT-IR studies. XRD patterns revealed that the nanoparticles were crystallized in hexagonal wurtzite structure with an average particle size of 19 nm to 26 nm. The surface morphology was explored using SEM micrographs. The incorporation of aluminum was confirmed by EDAX and FT-IR studies. The band gaps of the particles were found from 3.48 eV to 3.53 eV through UV-Vis spectral studies. The defect related mechanism was investigated using PL measurements. The chemical functional groups in FT-IR spectra proved the formation of pure and aluminum doped zinc oxide nanoparticles.

Keywords

  • zinc oxide nanoparticles
  • PL measurements
  • soft chemical method
Open Access

Preparation and characterization of EPDM-silica nano/micro composites for high voltage insulation applications

Published Online: 13 Mar 2015
Page range: 213 - 219

Abstract

Abstract

The rising market for substitute materials in high voltage insulation components is stimulated largely by the need to reduce overall costs. In this respect, polymer insulators offer significant advantages over old traditional materials. In the present research, efforts have been made to quantify the effect of silica (having different particle size nano, micro and hybrid) loading on the mechanical and thermal behaviors of Ethylene-Propylene-Diene Monomer (EPDM) based high voltage electrical insulations. The fabricated composites were subjected to mechanical, thermal and electrical properties measurements. The results of dielectric strength, surface and volume resistivities showed that all composites had insulator properties, while their mechanical and thermal properties improved considerably. EPDM was compounded with different types of silica in a two roll mill using sulphur cure system. The outcome achieved from the comparative study revealed that the EPDM nanocomposites had enhanced mechanical, thermal and electrical properties even at 5 % loadings.

Keywords

  • EPDM
  • nanocomposites
  • thermal stability
  • surface and volume resistivity
  • dielectric strength
30 Articles
Open Access

Two-phase synthesis of olive-like NiS particles and chain-like Bi2S3 nanowires

Published Online: 13 Mar 2015
Page range: 1 - 5

Abstract

Abstract

Highly dispersed olive-like NiS particles were synthesized in a liquid-liquid biphasic system at room temperature, where nickel xanthate in organic solvents (toluene and benzene) and sodium sulfide in water solution were used as nickel and sulfide sources, respectively. NiS particles were formed at the stabilized phase interface. The structures, chemical composition and optical characteristics of the products were investigated by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The organic solvents obviously influenced the morphology of the NiS particles. The olive-like NiS with smooth surface and sharp ends was obtained at benzene/water interface, while spindle-like NiS particles with rough surface and circle ends were formed when using toluene as a solvent. Analogously, chainlike Bi2S3 nanowires were produced at chloroform/water interface. The effect of the experiment parameters including reaction time, solvent and concentration of reactants on the size and morphology of the products was discussed in detail and a possible formation mechanism was suggested.

Keywords

  • two-phase method
  • crystal morphology
  • nanomaterials
  • semiconducting materials
Open Access

Antireflective bilayer coatings based on Al2O3 film for UV region

Published Online: 13 Mar 2015
Page range: 6 - 10

Abstract

Abstract

Bilayer antireflective coatings consisting of aluminium oxide Al2O3/MgF2 and Al2O3/SiO2 are presented in this paper. Oxide films were deposited by means of e-gun evaporation in vacuum of 5 × 10-3 Pa in the presence of oxygen, and magnesium fluoride was prepared by thermal evaporation on heated optical lenses made from quartz glass (Corning HPFS). Substrate temperature was maintained at 250 _C during the deposition. Thickness and deposition rate were controlled with a thickness measuring system Inficon XTC/2. The experimental results of the optical measurements carried out during and after the deposition process have been presented. Physical thickness measurements were made during the deposition process and resulted in 44 nm/52 nm for Al2O3/MgF2 and 44 nm/50 nm for Al2O3/SiO2 system. Optimization was carried out for ultraviolet region with minimum of reflectance at 300 nm. The influence of post deposition annealing on the crystal structure was determined by X-ray measurements. In the range from ultraviolet to the beginning of visible region, the reflectance of both systems decreased and reached minimum at 290 nm. The value of reflectance at this point, for the coating Al2O3/MgF2 was equal to R290nm = 0.6 % and for Al2O3/SiO2R290nm = 1.1 %. Despite the difference between these values both are sufficient for applications in the UV optical systems for medicine and UV laser technology.

Keywords

  • Al2O3/MgF2
  • Al2O3/SiO2
  • antireflective coatings
  • optical properties
Open Access

Influence of uniaxial stresses on electronic and optical properties of β-K2SO4 crystal

Published Online: 13 Mar 2015
Page range: 11 - 17

Abstract

Abstract

In view of possible practical applications of transparent crystals for mechanical stress sensors, theoretical investigation of piezo(elasto)optic effect in crystals might be useful for searching for proper materials, possessing large coefficients of elasto-optic effect, and for determination of uniaxial stress directions of maximum piezo-optical sensitivity. The influence of the uniaxial stresses on the electronic band structure, density of states, and optical properties of potassium sulphate crystal β-K2SO4 have been studied in the framework of the density functional theory using the ab initio CASTEP code. Increase in the band gap, Eg of the crystal takes place for three crystallographic directions and for moderate uniaxial stresses, σ < 1.5 GPa. Dependencies of principal refractive indices and polarizabilities upon principal uniaxial stresses are discussed together with other features of electronic structure of the crystal.

Keywords

  • crystals
  • insulators
  • electronic band structure
  • uniaxial stress
  • refractive indices
Open Access

Rietveld refinement on XRD and TEM study of nanocrystalline PbZr0:5Ti0:5O3 ceramics prepared with a soft chemistry route

Published Online: 13 Mar 2015
Page range: 18 - 24

Abstract

Abstract

PbZr0:5Ti0:5O3 nanopowders (~27 nm) have been prepared by a controlled reconstructive thermal decomposition and crystallization from an amorphous polymeric precursor with polyvinyl alcohol (PVA) and sucrose at 400 to 700 °C in air. The Rietveld refinement of the XRD profiles which were recorded at room temperature for the PbZr0:5Ti0:5O3 powder prepared by a thermal treatment at 700 °C for 2 h, confirmed the P4mm tetragonal crystal structure of the as prepared PbZr0:5Ti0:5O3 nanopowders, with a = 0.4036 nm and c = 0.4147 nm. A hexagonal symmetry (R3c), with a = 0.5774 nm and c = 1.4212 nm, was also detected from Rietveld refinement analysis. Thus, tetragonal and hexagonal phases were found to coexist with the as prepared PbZr0:5Ti0:5O3 nanopowders. The average particle size (D) of the PbZr0:5Ti0:5O3 powders, estimated with the help of the specific surface area, measured by BET method, was 26.1 nm. Average D value, calculated by D2θ1/2 in the XRD peaks with the Debye-Scherrer relation was ~24 nm. TEM study made it possible to measure the particle size of PbZr0:5Ti0:5O3 powders with an average diameter of 27 nm.

Keywords

  • precursor method
  • PbZr0:5Ti0:5O3 nanopowders
  • tetragonal phase
  • PVA-sucrose
  • ferroelectrics
Open Access

Electrochemical behavior and conductivity measurements of electropolymerized selenophene-based copolymers

Published Online: 13 Mar 2015
Page range: 25 - 35

Abstract

Abstract

Electrochemical copolymerization of selenophene and thiophene was performed at a constant electrode potential. The obtained homopolymer films and copolymers were studied and characterized with cyclic voltammetry and conductivity measurements, from which conductivity values around 13.35 S · cm-1 were determined. The influence of the applied electropolymerization potential and the monomer feed ratio of selenophene and thiophene on the copolymers properties was investigated. The obtained copolymers showed good stability of the redox activity in an acetonitrile-based electrolyte solution. At higher polymerization potentials and at higher concentrations of thiophene in the feed, more thiophene units were incorporated into the copolymer chain. The conductivities of the copolymers were between those of homopolymers, implying that oxidation of both monomers was possible and the copolymer chains might accordingly be composed of both selenophene and thiophene units.

Keywords

  • electropolymerization
  • intrinsically conducting polymers
  • polythiophene
  • polyselenophene
Open Access

Influence of duration time of CVD process on emissive properties of carbon nanotubes films

Published Online: 13 Mar 2015
Page range: 36 - 46

Abstract

Abstract

In this paper various types of films made of carbon nanotubes (CNTs) are presented. These films were prepared on different substrates (Al2O3, Si n-type) by the two-step method. The two-step method consists of physical vapor deposition step, followed by chemical vapor deposition step (PVD/CVD). Parameters of PVD process were the same for all initial films, while the duration times of the second step - the CVD process, were different (15, 30 min.). Prepared films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and field emission (FE) measurements. The I-E and F-N characteristics of electron emission were discussed in terms of various forms of CNT films. The value of threshold electric field ranged from few V/μm (for CNT dispersed rarely on the surface of the film deposited on Si) up to ~20 V/μm (for Al2O3 substrate).

Keywords

  • carbon nanotubes film
  • field emission
  • SEM
  • TEM
Open Access

Synthesis of SiO2 nanopowders containing quartz and cristobalite phases from silica sands

Published Online: 13 Mar 2015
Page range: 47 - 55

Abstract

Abstract

In this study, extraction and synthesis of SiO2 nanoparticles from silica sands have been conducted by means of two different methods, i.e. dry method (method 1) and hydrothermal process (method 2). The basic difference between the two methods is in the extraction step. The two methods were compared in terms of being more efficient, economical, and superior in obtaining SiO2 nanoparticles. The SiO2 nanoparticles were characterized in terms of phase purity, crystallinity, Si-O functional bonding as well as particles size and morphology. The most interesting fact in this study was the formation of both quartz and cristobalite phases within all prepared SiO2 nanoparticles.

Keywords

  • silica sand
  • SiO2 nanoparticles
  • quartz and cristobalite phases
Open Access

Hydrogen permeation properties of Pd-coated Pd33Ni52Si15 amorphous alloy membrane

Published Online: 13 Mar 2015
Page range: 56 - 58

Abstract

Abstract

The vast majority of experimental techniques used for the measurements of hydrogen permeability through metallic membranes whose one or both surfaces are covered with a thin Pd film is based on the assumption that a ratio of film-to-membrane thickness is small enough to cause hydrogen flow to be independent of the Pd film thickness. In an attempt to verify this assumption, we have measured the hydrogen flow through the Pd33Ni52Si15 amorphous membrane covered with Pd film of 10, 20, and 30 nm in thickness. Contrary to our expectations, we have found a dramatic decrease in hydrogen flow with the increase in Pd film thickness. Our findings are discussed in terms of potential barrier between the two different phases.

Keywords

  • permeability
  • hydrogen
  • palladium alloys
  • membrane
  • metallic glasses
Open Access

Green synthesis and characterization of Ag1/2Al1/2TiO3 nanoceramics

Published Online: 13 Mar 2015
Page range: 59 - 72

Abstract

Abstract

Single phase silver aluminum titanate (Ag1/2Al1/2)TiO3, later called AAT, nanoceramic powder (particle size 2 to 7.5 nm) was synthesized by a low-cost, green and reproducible tartaric acid gel process. X-ray, FT-IR, energy dispersive X-ray and high resolution transmission electron microscopy analyses were performed to ascertain the formation of AAT nanoceramics. X-ray diffraction data analysis indicated the formation of monoclinic structure having the space group P2/m(10). UV-Vis study revealed the surface plasmon resonance at 296 nm. Dielectric study revealed that AAT nanoceramics could be a suitable candidate for capacitor applications and meets the specifications for “Z7R” of Class I dielectrics of Electronic Industries Association. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were performed using the impedance data. Electric modulus studies supported the hopping type of conduction in AAT. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in AAT. The ac conductivity data were used to evaluate the density of states at Fermi level and minimum hopping length of the compound.

Keywords

  • electronic materials
  • oxides
  • chemical synthesis
  • dielectric properties
  • electrical properties
Open Access

Magnetoresistance peculiarities and magnetization of materials with two kinds of superconducting inclusions

Published Online: 13 Mar 2015
Page range: 73 - 81

Abstract

Abstract

Low-temperature properties of a crystal containing type I superconducting inclusions of two different materials have been studied. In the approximation assuming that the inclusions size is much smaller than the coherence length/penetration depth of the magnetic field, the theory of magnetoresistance of a crystal containing spherical superconducting inclusions of two different materials has been developed, and magnetization of crystals has been calculated. The obtained results can be used for correct explanation of the low temperature conductivity in binary and more complex semiconductors, in which precipitation of the superconducting phase is possible during the technological processing or under external impact.

Keywords

  • spherical superconducting inclusion
  • magnetoresistance
  • magnetization
  • type I superconductors
Open Access

Computer simulation of sputtering of graphite target in magnetron sputtering device with two zones of erosion

Published Online: 13 Mar 2015
Page range: 82 - 94

Abstract

Abstract

A computer simulation program for discharge in a magnetron sputtering device with two erosion zones was developed. Basic laws of the graphite target sputtering process and transport of sputtered material to the substrate were taken into account in the Monte Carlo code. The results of computer simulation for radial distributions of density and energy flux of carbon atoms on the substrate (at different values of discharge current and pressure of the working gas) confirmed the possibility of obtaining qualitative homogeneous films using this magnetron sputtering device. Also the discharge modes were determined for this magnetron sputtering device, in which it was possible to obtain such energy and density of carbon atoms fluxes, which were suitable for deposition of carbon films containing carbon nanotubes and other nanoparticles.

Keywords

  • Monte Carlo computer simulation
  • magnetron sputtering
  • flux of particles
  • carbon
  • graphite target
  • energy of particles
Open Access

Phase, microstructure and microwave dielectric properties of Mg0:95Ni0:05Ti0:98Zr0:02O3 ceramics

Published Online: 13 Mar 2015
Page range: 95 - 99

Abstract

Abstract

Mg0:95Ni0:05Ti0:98Zr0:02O3 ceramics was prepared via conventional solid-state mixed-oxide route. The phase, microstructure and microwave dielectric properties of the sintered samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and a vector network analyzer. The microstructure comprised of circular and elongated plate-like grains. The semi quantitative analysis (EDS) of the circular and elongated grains revealed the existence of Mg0:95Ni0:05T2O5 as a secondary phase along with the parent Mg0:95Ni0:05Ti0:98Zr0:02O3 phase, which was consistent with the XRD findings. In the present study, εr ~17.1, Qufo~195855 ± 2550 GHz and τf ~ -46 ppm/K was achieved for the synthesized Mg0:95Ni0:05Ti0:98Zr0:02O3 ceramics sintered at 1325 °C for 4 h.

Keywords

  • phase
  • microstructures
  • ceramics
Open Access

Influence of different synthesis conditions on properties of oleic acid-coated-Fe3O4 nanoparticles

Published Online: 13 Mar 2015
Page range: 100 - 106

Abstract

Abstract

In the present paper, iron oxide nanoparticles coated by oleic acid have been synthesized in different conditions by coprecipitation method. For investigating the effect of time spent on adding the oleic acid to the precursor solution, two different processes have been considered. The as synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Magnetic measurement was carried out at room temperature using a vibrating sample magnetometer (VSM). The results show that the magnetic nanoparticles decorated with oleic acid decreased the saturation of magnetization. From the data, it can also be concluded that the magnetization of Fe3O4/oleic acid nanoparticles depends on synthesis conditions.

Keywords

  • co-precipitation
  • super-paramagnetic nanoparticles
  • oleic acid
  • strain
  • magnetite
Open Access

Magnetoelectric effect in (BiFeO3)x–(BaTiO3)1-x solid solutions

Published Online: 13 Mar 2015
Page range: 107 - 112

Abstract

Abstract

The aim of the present work was to study magnetoelectric effect (ME) in (BiFeO3)x-(BaTiO3)1-x solid solutions in terms of technological conditions applied in the samples fabrication process. The rapidly growing interest in these materials is caused by their multiferroic behaviour, i.e. coexistence of both electric and magnetic ordering. It creates possibility for many innovative applications, e.g. in steering the magnetic memory by electric field and vice versa. The investigated samples of various chemical compositions (i.e. x = 0.7, 0.8 and 0.9) were prepared by the solid-state sintering method under three sets of technological conditions differing in the applied temperature and soaking time. Measurements of the magnetoelectric voltage coefficient αME were performed using a dynamic lock-in technique. The highest value of αME was observed for 0.7BiFeO3-0.3BaTiO3 solid solution sintered at the highest temperature (T = 1153 K) after initial electrical poling despite that the soaking time was reduced 10 times in this case.

Keywords

  • magnetoelectric effect
  • multiferroic materials
  • magnetoelectric voltage coefficient
Open Access

Reactive bay functionalized perylene monoimide-polyhedral oligomeric silsesquioxane organic electronic dye

Published Online: 13 Mar 2015
Page range: 113 - 121

Abstract

Abstract

Aggregation-induced quenching is particularly detrimental in perylene diimides, which are characterized by a near-unity fluorescence quantum yield in solution but are far less emissive in the solid state. Previously, perylene diimide has been improved by linking it to the inorganic cage of polyhedral oligomeric silsesquioxanes. As a further study on perylene diimidepolyhedral oligomeric silsesquioxanes, we report on a double functionalized molecular structure, which can be used for substitution at the bay area and as a side group in other materials. Typical solution absorption and emission features of the perylene diimide fragment have been observed in this new reactive perylene diimide-polyhedral oligomeric silsesquioxane. Moreover, reduced stacking during aggregation and spherical particles exhibiting solid fluorescence have been obtained. Organic semiconducting material with enhanced solid state photophysical properties, like solid fluorescence is a subject of great interest owing to its possible high-tech applications in optoelectronic devices.

Keywords

  • perylene diimides
  • polyhedral oligomeric silsesquioxane
  • fluorescence
  • optoelectronics
  • self assembly
Open Access

Analysis of emission of Eu3+ and Dy3+ doped Magnesium Boro-Tellurite (MBT) ceramics

Published Online: 13 Mar 2015
Page range: 122 - 125

Abstract

Abstract

Rare earth (RE) ions play an important role in the improvement of the optical properties of ceramics. Rare-earth ceramics are commonly used in display panels, fluorescent lamps and lasers. The luminescence properties of Magnesium Boro-Tellurite (MBT) Eu3+ and Dy3+ doped ceramics have not been reported before. Therefore, the aim of this paper is to determine the effect of different compositions on the luminescence properties of the MBT material. A series of xTeO2-(70-x)B2O3-30MgO ceramics with 10 ≤ x ≤ 40 mol % doped with 1 mol % of Eu3+ and Dy3+ ions was prepared via the solid-state reaction method. The influence of various compositions on the crystalline phase and photoluminescence properties of the samples were investigated by X-ray diffraction (XRD) and luminescence spectroscopy. The crystalline phases obtained in this study are Mg3(BO3)2, MgB4O7, Mg2B2O5, Mg(Te2O5) and MgTe3O6. It was stated that the crystalline phases have not changed as a result of doping with Eu3+ and Dy3+ ions. The emission spectra of Eu3+: MBT ceramics showed strong red emission at 612 nm due to the transition of 5D07F2 and meanwhile, the Dy3+: MBT ceramics showed a blue emission at 480 nm due to 4F9/2 6H15/2 transition and yellow emission at 576 nm due to 4F9/26H13/2 transition. Both the rare-earth doped phosphors showed bright emission.

Keywords

  • Magnesium Boro-Tellurite (MBT)
  • luminescence
  • ceramics
Open Access

Phase, microstructure and microwave dielectric properties of A-site deficient (La, Nd)2/3TiO3 perovskite ceramics

Published Online: 13 Mar 2015
Page range: 126 - 130

Abstract

Abstract

(La, Nd)2/3TiO3 ceramics were prepared through a conventional solid state mixed oxide route. For phase and microstructure analysis, XRD and SEM were used, respectively. Microwave dielectric properties were measured using a network analyzer. XRD patterns revealed the formation of the parent (La, Nd)2/3TiO3 phase along with (La, Nd)4Ti9O24 as a secondary phase. The microstructure consisted of rectangular and needle shaped grains, which decreased in size from 4 μm to 2 μm with an increase in sintering temperature from 1300 °C to 1350 °C. Decrease in grain size caused an increase in density of the samples from 4.81 g/cm3 to 5.17 g/cm3. Microwave dielectric properties of the samples calcined and sintered in air atmosphere were εr = 40.35, Q × f = 3499 GHz and τf = 0 ppm/°C, whereas for a sample calcined in nitrogen and sintered in air they were εr = 40.18, Q × f = 4077 GHz and τf = +4.9 ppm/°C, respectively.

Keywords

  • A-site deficient perovskites
  • dielectrics
  • phase analysis
  • ceramics
Open Access

Evaluation of the acid properties of aluminossilicate MCM-22 material synthesized under static conditions

Published Online: 13 Mar 2015
Page range: 131 - 136

Abstract

Abstract

The hydrothermal synthesis of MCM-22 zeolite was carried out using silica, sodium aluminate and hexamethyleneimine, under static conditions at 150 °C for a period of 10 days, followed by washing with deionized water, drying overnight and calcination at 650 °C. The obtained material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The XRD analysis evidenced that MCM-22 presented a well defined MWW structure. The FT-IR spectrum confirmed the efficiency of the hexamethyleneimine as an organic template used to direct the structure of the MCM-22 zeolite under static conditions. The SEM image indicated that the particles are spherical in shape, with a diameter of ca. 10 μm. The acid properties of the MCM-22 zeolite, as determined by n-buthylamine adsorption, were investigated in the temperature ranges of 105 to 300 °C and 300 to 525 °C, relative to medium and strong acid sites, respectively.

Keywords

  • crystal structure
  • synthesis of zeolites
  • porous materials
  • MCM-22
Open Access

Surface morphology of titanium nitride thin films synthesized by DC reactive magnetron sputtering

Published Online: 13 Mar 2015
Page range: 137 - 143

Abstract

Abstract

In this paper the influence of temperature on the 3-D surface morphology of titanium nitride (TiN) thin films synthesized by DC reactive magnetron sputtering has been analyzed. The 3-D morphology variation of TiN thin films grown on p-type Si (100) wafers was investigated at four different deposition temperatures (473 K, 573 K, 673 K, 773 K) in order to evaluate the relation among the 3-D micro-textured surfaces. The 3-D surface morphology of TiN thin films was characterized by means of atomic force microscopy (AFM) and fractal analysis applied to the AFM data. The 3-D surface morphology revealed the fractal geometry of TiN thin films at nanometer scale. The global scale properties of 3-D surface geometry were quantitatively estimated using the fractal dimensions D, determined by the morphological envelopes method. The fractal dimension D increased with the substrate temperature variation from 2.36 (at 473 K) to 2.66 (at 673 K) and then decreased to 2.33 (at 773 K). The fractal analysis in correlation with the averaged power spectral density (surface) yielded better quantitative results of morphological changes in the TiN thin films caused by substrate temperature variations, which were more precise, detailed, coherent and reproducible. It can be inferred that fractal analysis can be easily applied for the investigation of morphology evolution of different film/substrate interface phases obtained using different thin-film technologies.

Keywords

  • atomic force microscopy (AFM)
  • DC reactive magnetron sputtering
  • fractal analysis
  • surface roughness
  • titanium nitride (TiN) thin film
Open Access

Infrared luminescence and thermoluminescence of lithium borate glasses doped with Sm3+ ions

Published Online: 13 Mar 2015
Page range: 144 - 151

Abstract

Abstract

Thermoluminescence (TL) characteristics of X-ray irradiated pure and doped with Sm3+ ions Li2O-MO-B2O3 (where MO=ZnO, CaO, CdO) glasses have been studied in the temperature range of 303 to 573 K. All the pure glasses exhibited single TL peaks at 382 K, 424 K and 466 K. When these glasses were doped with Sm3+ ions no additional peaks have been observed but the glow peak temperature of the existing glow peak shifted gradually towards higher temperatures with gain in intensity of TL light output. The area under the glow curve was found to be maximum for Sm3+ doped glasses mixed with cadmium oxide as a modifier. The trap depth parameters associated with the observed TL peaks have been evaluated using Chen’s formulae. The possible use of these glasses in radiation dosimetry has been described. The results clearly showed that samarium doped cadmium borate glass has a potential to be considered as a thermoluminescence dosimeter.

Keywords

  • infrared spectra
  • thermoluminescence
  • borate glasses
  • samarium ions
Open Access

High temperature thermoelectric properties of PbTe prepared by high pressure method

Published Online: 13 Mar 2015
Page range: 152 - 156

Abstract

Abstract

Highly dispersed olive-like NiS particles were synthesized in a liquid-liquid biphasic system at room temperature, where nickel xanthate in organic solvents (toluene and benzene) and sodium sulfide in water solution were used as nickel and sulfide sources, respectively. NiS particles were formed at the stabilized phase interface. The structures, chemical composition and optical characteristics of the products were investigated by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The organic solvents obviously influenced the morphology of the NiS particles. The olive-like NiS with smooth surface and sharp ends was obtained at benzene/water interface, while spindle-like NiS particles with rough surface and circle ends were formed when using toluene as a solvent. Analogously, chainlike Bi2S3 nanowires were produced at chloroform/water interface. The effect of the experiment parameters including reaction time, solvent and concentration of reactants on the size and morphology of the products was discussed in detail and a possible formation mechanism was suggested.

Keywords

  • thermoelectric material
  • high pressure
  • PbTe
Open Access

Effect of fabrication technique on the crystalline phase and electrical properties of PVDF films

Published Online: 13 Mar 2015
Page range: 157 - 162

Abstract

Abstract

The effect of different fabrication techniques on the formation of electroactive β-phase polyvinylidene fluoride (PVDF) has been investigated. Films with varying concentration of PVDF and solvent - dimethyl formamide (DMF) were synthesized by tape casting and solvent casting techniques. The piezoelectric β-phase as well as non polar β-phase were observed for both the tape cast and solvent cast films from X-ray diffraction (XRD) micrographs and Fourier transform infra-red spectroscopy (FT-IR) spectra. A maximum percentage (80 %) of β-phase was obtained from FT-IR analysis for a solvent cast PVDF film. The surface morphology of the PVDF films was analyzed by FESEM imaging. The dielectric properties as a function of temperature and frequency and the ferroelectric hysteresis loop as a function of voltage were measured. An enhancement in the value of the dielectric constant and polarization was obtained in solvent cast films.

Keywords

  • PVDF
  • crystallinity
  • dielectric
  • remanent polarization
Open Access

Nanosized MoO3 as a reusable heterogeneous catalyst for the synthesis of 2,6-bis(benzylidene)cyclohexanones

Published Online: 13 Mar 2015
Page range: 163 - 168

Abstract

Abstract

Crystalline MoO3 nanoparticles were obtained by electrochemical synthesis process using tetrapropylammonium bromide as a stabilizer and structure-directing agent in ACN:THF(4:1) solvent. Formation of MoO3 nanoparticles took place at a constant supply current of 14 mA/cm2. These synthesized MoO3 nanoparticles were characterized by UV-Vis spectroscopy, FT-IR spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM). So prepared MoO3 nanoparticles were used as a heterogeneous catalyst for the synthesis of 2,6-bis(benzylidene)cyclohexanone derivatives. This protocol offers several advantages, such as simple work-up procedure, recyclability of the catalyst, excellent product yield in a short reaction time and purification of products with a non-chromatographic method.

Keywords

  • electrochemical synthesis
  • MoO3 nanoparticles
  • heterogeneous catalyst
  • 2,6-bis(benzylidene)cyclohexanone
Open Access

First principles study of structure, electronic and optical properties of Y3Fe5O12 in cubic and trigonal phases

Published Online: 13 Mar 2015
Page range: 169 - 174

Abstract

Abstract

First principles calculations have been performed to investigate the structure, electronic and optical properties of Y3Fe5O12. Both the cubic and trigonal phases have been considered in our calculation. The calculated structural parameters are slightly larger than the experimental values. The band structures show that Y3Fe5O12 in cubic and trigonal phases have direct band gaps of 0.65 and 0.17 eV. The calculations of dielectric function, absorption, extinction coefficient, refractive index, energy loss function and reflectivity are presented.

Keywords

  • Y3Fe5O12
  • first principles
  • electronic structure
  • optical properties
Open Access

Morphological features in aluminum nitride epilayers prepared by magnetron sputtering

Published Online: 13 Mar 2015
Page range: 175 - 184

Abstract

Abstract

The aim of this study is to characterize the surface topography of aluminum nitride (AlN) epilayers prepared by magnetron sputtering using the surface statistical parameters, according to ISO 25178-2:2012. To understand the effect of temperature on the epilayer structure, the surface topography was investigated through atomic force microscopy (AFM). AFM data and analysis of surface statistical parameters indicated the dependence of morphology of the epilayers on their growth conditions. The surface statistical parameters provide important information about surface texture and are useful for manufacturers in developing AlN thin films with improved surface characteristics. These results are also important for understanding the nanoscale phenomena at the contacts between rough surfaces, such as the area of contact, the interfacial separation, and the adhesive and frictional properties.

Keywords

  • aluminum nitride epilayer
  • atomic force microscopy
  • magnetron sputtering
  • substrate
  • surface roughness
Open Access

Synthesis, characterization and fabrication of copper nanoparticles in N-isopropylacrylamide based co-polymer microgels for degradation of p-nitrophenol

Published Online: 13 Mar 2015
Page range: 185 - 192

Abstract

Abstract

Poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAM-co-AAc)] microgels were synthesized by precipitation polymerization. Copper nanoparticles were successfully fabricated inside the microgels by in-situ reduction of copper ions in an aqueous medium. The microgels were characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and Dynamic Light Scattering (DLS). Hydrodynamic radius of P(NIPAM-co-AAc) microgel particles increased with an increase in pH in aqueous medium at 25 °C. Copper-poly(N-isopropylacrylamide-co-acrylic acid) [Cu-P(NIPAM-co-AAc)] hybrid microgels were used as a catalyst for the reduction of 4-nitrophenol (4-NP). Effect of temperature, concentration of sodium borohydride (NaBH4) and catalyst dosage on the value of apparent rate constant (kapp) for catalytic reduction of 4-NP in the presence of Cu-P(NIPAM-co-AAc) hybrid microgels were investigated by UV-Vis spectrophotometry. It was found that the value of kapp for catalytic reduction of 4-NP in the presence of Cu-P(NIPAM-co-AAc) hybrid microgel catalyst increased with an increase in catalyst dosage, temperature and concentration of NaBH4 in aqueous medium. The results were discussed in terms of diffusion of reactants towards catalyst surface and swelling-deswelling of hybrid microgels.

Keywords

  • microgels
  • copper
  • nitrophenol
  • catalysis
  • energy of activation
Open Access

Synthesis of polyaniline nanotubes through UV light catalytic method

Published Online: 13 Mar 2015
Page range: 193 - 197

Abstract

Abstract

In this study, nitrocellulose (NC) fiber blanket prepared by electrostatic spinning method has been used as a template, and copper nitrate (Cu(NO3)2) as an oxidant to synthesise polyaniline nanotubes doped with heteropolyacid (H4SiW12O40, SiW12) using UV light catalytic method. Infrared spectroscopy (IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) technologies were applied to characterize the prepared samples of polyaniline nanotubes. The results show that the external diameter of the tube is about 200 nm, and the internal diameter about 170 nm. We also give a reasonable speculation and explanation about the formation mechanism of the nanotubes.

Keywords

  • UV irradiation
  • polyaniline
  • nanotubes
  • template
  • heteropolyacid
Open Access

Influence of aluminium concentration in Zn0:9V0:1O nanoparticles on structural and optical properties

Published Online: 13 Mar 2015
Page range: 198 - 204

Abstract

Abstract

The (V,Al) co-doped ZnO nano-structured powders (Zn0.9-xV0.1AlxO, where x = 0.02, 0.03 and 0.04) were synthesized via the sol-gel technique and their structural and optical properties were investigated. The effect of Al concentration on the structural and optical properties of the Zn0.9-xV0.1AlxO nanopowders was studied using various techniques. The XRD patterns indicate that the samples have a polycrystalline wurtzite structure. The crystallite size increases with increasing the Al content and lies in the range of 23 to 30 nm. The lattice strain, estimated by the Stokes-Wilson equation, decreases when Al content increases. SEM and TEM micrographs show that Zn0.9-xV0.1AlxO powders are the agglomeration of nanoparticles having spherical and hexagonal shapes with dimensions ranging from 20 to 30 nm. FT-IR spectra show a distinct absorption peak at about 500 cm-1 for ZnO stretching modes and other peaks related to OH and H2O bands. Raman spectra confirm the wurtzite structure of the Zn0.9-xV0.1AlxO nanoparticles. The direct band gaps of the synthesized Zn0.9-xV0.1AlxO nanopowders, estimated from the Brus equation and the crystallite sizes deduced from XRD, are around 3.308 eV. The decomposition process of the dried gel system was investigated by thermal gravimetric analysis (TGA).

Keywords

  • ZnO nanopowder
  • V and Al co-doping
  • XRD
  • TEM
  • Raman scattering
Open Access

Investigation on room temperature photoluminescence of pure and aluminum doped zinc oxide nanoparticles

Published Online: 13 Mar 2015
Page range: 205 - 212

Abstract

Abstract

Pure and aluminum doped zinc oxide nanoparticles were prepared by soft chemical method. The prepared nanoparticles were characterized by XRD, SEM-EDAX, UV-Vis, PL and FT-IR studies. XRD patterns revealed that the nanoparticles were crystallized in hexagonal wurtzite structure with an average particle size of 19 nm to 26 nm. The surface morphology was explored using SEM micrographs. The incorporation of aluminum was confirmed by EDAX and FT-IR studies. The band gaps of the particles were found from 3.48 eV to 3.53 eV through UV-Vis spectral studies. The defect related mechanism was investigated using PL measurements. The chemical functional groups in FT-IR spectra proved the formation of pure and aluminum doped zinc oxide nanoparticles.

Keywords

  • zinc oxide nanoparticles
  • PL measurements
  • soft chemical method
Open Access

Preparation and characterization of EPDM-silica nano/micro composites for high voltage insulation applications

Published Online: 13 Mar 2015
Page range: 213 - 219

Abstract

Abstract

The rising market for substitute materials in high voltage insulation components is stimulated largely by the need to reduce overall costs. In this respect, polymer insulators offer significant advantages over old traditional materials. In the present research, efforts have been made to quantify the effect of silica (having different particle size nano, micro and hybrid) loading on the mechanical and thermal behaviors of Ethylene-Propylene-Diene Monomer (EPDM) based high voltage electrical insulations. The fabricated composites were subjected to mechanical, thermal and electrical properties measurements. The results of dielectric strength, surface and volume resistivities showed that all composites had insulator properties, while their mechanical and thermal properties improved considerably. EPDM was compounded with different types of silica in a two roll mill using sulphur cure system. The outcome achieved from the comparative study revealed that the EPDM nanocomposites had enhanced mechanical, thermal and electrical properties even at 5 % loadings.

Keywords

  • EPDM
  • nanocomposites
  • thermal stability
  • surface and volume resistivity
  • dielectric strength

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