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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 2 (June 2015)

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

Search

29 Articles
Open Access

Grain growth kinetics for B2O3-doped ZnO ceramics

Published Online: 11 Jul 2015
Page range: 220 - 229

Abstract

Abstract

Grain growth kinetics in 0.1 to 2 mol % B2O3-added ZnO ceramics was studied by using a simplified phenomenological grain growth kinetics equation Gn = K0 · t · exp(-Q/RT) together with the physical properties of sintered samples. The samples, prepared by conventional ceramics processing techniques, were sintered at temperatures between 1050 to 1250 °C for 1, 2, 3, 5 and 10 hours in air. The kinetic grain growth exponent value (n) and the activation energy for the grain growth of the 0.1 mol % B2O3-doped ZnO ceramics were found to be 2.8 and 332 kJ/mol, respectively. By increasing B2O3 content to 1 mol %, the grain growth exponent value (n) and the activation energy decreased to 2 and 238 kJ/mol, respectively. The XRD study revealed the presence of a second phase, Zn3B2O6 formed when the B2O3 content was > 1 mol %. The formation of Zn3B2O6 phase gave rise to an increase of the grain growth kinetic exponent and the grain growth activation energy. The kinetic grain growth exponent value (n) and the activation energy for the grain growth of the 2 mol % B2O3-doped ZnO ceramics were found to be 3 and 307 kJ/mol, respectively. This can be attributed to the second particle drag (pinning) mechanism in the liquid phase sintering.

Keywords

  • boron oxide
  • grain growth
  • zinc oxide
Open Access

Synthesis and photocatalytic performance of spongy ZnO microstructures

Published Online: 11 Jul 2015
Page range: 230 - 236

Abstract

Abstract

Spongy ZnO microstructures were synthesized via a facile hydrothermal method using zinc nitrate hexahydrate and oxalic acid as raw materials. The as-obtained ZnO were characterized by powder X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and transmission electron spectroscopy (TEM), respectively. The BET surface area and average pore size of the samples were determined by nitrogen adsorption-desorption analysis. Effects of precursor and hydrothermal temperature on the morphology and photocatalytic activity of the products were investigated. SEM and TEM analysis indicated that the as-obtained spongy ZnO microstructures consisted of a large amount of ZnO particles with the average size of about 100 to 150 nm. The photocatalytic activities of the spongy ZnO microstructures were evaluated by photodegradation of methylene blue (MB) under UV light radiation. The results indicated that the ZnO synthesized at 150 °C for 10 h showed the highest photocatalytic activity and the degradation ratio of MB reached 99.5 % for 60 min of UV light irradiation with the light intensity of 10 mW · cm-2.

Keywords

  • ZnO
  • spongy structures
  • hydrothermal method
  • microstructures
Open Access

Improved efficiency of dye-sensitized solar cells by doping of strontium aluminate phosphor in TiO2 photoelectrode

Published Online: 11 Jul 2015
Page range: 237 - 241

Abstract

Abstract

SrAl2O4:Eu2+, Dy3+ phosphor was synthesized by chemical solution route to use as a dopant in TiO2 layer employed as a photoelectrode for down conversion of ultraviolet and near-ultraviolet to visible and near-infrared light in a dye-sensitized solar cell. Nano-crystalline structure of the SrAl2O4:Eu2+, Dy3+ powder was confirmed by X-ray diffraction analysis and field emission scanning electron microscopy. Monitored at 520 nm, SrAl2O4:Eu2+, Dy3+ phosphor showed emission peaks at 460 to 610 nm due to 4f6 4f7 transitions of Eu2+ ions. For the study, SrAl2O4:Eu2+, Dy3+ phosphor-doped TiO2 layer was deposited on fluorine-doped tin oxide coated glass by electrostatic spray deposition. The short circuit current, open circuit voltage, fill factor, and conversion efficiency of the cells were measured. Experimental results revealed that the device efficiency for the SrAl2O4:Eu2+, Dy3+ phosphor-doped TiO2 layer increased to 7.20 %, whereas that of the pure-TiO2 photoelectrode was 4.13 %.

Keywords

  • phosphor
  • down conversion
  • dye-sensitized solar cell
Open Access

Synthesis and electrical properties of silver nanoplates for electronic applications

Published Online: 11 Jul 2015
Page range: 242 - 250

Abstract

Abstract

In this paper, silver nanoplates of 100 to 500 nm size were synthesized by reduction of silver nitrate with N,Ndimethylformamide, using poly(vinylpyrolidone) as a surfactant and ferric chloride as a controlling agent, at 120 to 160 °C for 5 to 24 hours. The influence of the concentration of ferric chloride, the reaction temperature and reaction time on the morphology of the product has been investigated by transmission electron microscopy, scanning electron microscopy and UV-Vis spectroscopy. The results indicated that the products obtained at the low reaction temperature and short reaction time in the presence of FeCl3 in the reaction solution were in the form of silver nanoplates, whose morphology was mainly triangular and hexagonal. In addition, the size and thickness of the nanoplates increased with increasing of the FeCl3 concentration. At a high reaction temperature and long reaction time, the truncated triangle and hexagonal nanoplates were mainly produced. Furthermore, the sintering behavior of nanoplates was studied and the results showed that sintering of the silver nanoplates started at 180 °C, and a typical sintering behavior was observed at higher temperatures. The incorporation of the silver nanoplates into the polymer matrix with micro-sized silver flakes led to an increase in the matrix resistivity in almost all cases, especially at high fractions and low curing temperatures. The curing temperature had an influence on the resistivity of the conductive adhesives filled with micro-sized silver flakes and silver nanoplates due to sintering of the silver nanoplates.

Keywords

  • silver nanoplates
  • solvothermal process
  • controlling agent
  • sintering behavior
  • electrical properties
Open Access

First-principle investigations of structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides

Published Online: 11 Jul 2015
Page range: 251 - 258

Abstract

Abstract

In the present work, we have investigated the structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides in the B2 structure, using first-principle calculations of the density functional theory (DFT) based on the linearized augmented plane wave method (FP-LAPW) as implemented in the WIEN2k code, in which the energy of exchange and correlation are treated by the generalized gradient approximation (GGA), proposed in 1996 by Perdew, Burke and Ernzerhof (PBE). The ground state properties have been calculated and compared with other calculations, and the electronic structures of all FeAl, CoAl, and NiAl compounds exhibited a metallic behavior. It was depicted that the density of states is characterized by the large hybridization between the s-p (Al) and 3d (Fe, Co, and Ni) states, which creates the pseudogap in the region of anti-bonding states. Moreover, the band structures of FeAl, CoAl, and NiAl are similar to each other and the difference between them is in the energy level of each band relative to the Fermi level.

Keywords

  • first-principle calculations
  • intermetallics
  • electronic structures
Open Access

Frequency and temperature dependent transport properties of NiCuZn ceramic oxide

Published Online: 11 Jul 2015
Page range: 259 - 267

Abstract

Abstract

A polycrystalline sample of ceramic oxide Ni0.27Cu0.10Zn0.63Fe2O4 was prepared by the solid state reaction method. The sintered sample was well polished to remove any oxide layer formed during sintering and the two surfaces of the pellet were coated with a silver paste as a contact material. Among dielectric properties, complex dielectric constant (ε* = εʹ - jεʺ), loss tangent (tanδ) and ac conductivity (σac) in the frequency range of 20 Hz to 2 MHz were analyzed in the temperature range of 303 to 498 K using a Wayne Kerr impedance analyzer (model No. 6500B). The experimental results indicate that ε, εʺ, tanδ and σac decrease with an increase in frequency and increase with increasing temperature. The transition temperature, as obtained from dispersion curve of εʹ, shifts towards higher temperature with an increase in frequency. The variation of dielectric properties with frequency and temperature shows the dispersion behavior which is explained in the light of Maxwell-Wagner type of interfacial polarization in accordance with the Koop’s phenomenological theory. The frequency dependent conductivity results satisfy the Jonscher’s power law, σT(ω) = σ(o)+Aωn, and the results show the occurrence of two types of conduction process at elevated temperature: (i) low frequency conductivity, due to long-range ordering (frequency independent, region I), (ii) mid frequency conductivity at the grain boundaries (region II, dispersion) and (iii) high frequency conductivity at the grain interior due to the short-range hopping mechanism (frequency independent plateau, region III).

Keywords

  • NiCuZn ferrite
  • dielectric properties
  • ac conductivity
  • frequency and temperature dependence
Open Access

Frequency and temperature dependence of dielectric and electric properties of Ba2-xSm4+2x/3Ti8O24 with structural analysis

Published Online: 11 Jul 2015
Page range: 268 - 277

Abstract

Abstract

Dielectric ceramics samples of barium titanium oxide doped with samarium, having a complex structural formula of Ba2-xSm4+2x/3Ti8O24 (referred to as BST), were fabricated by a high temperature solid-state reaction technique with varying x (0.0, 0.2, 0.4, 0.6). X-ray diffraction technique was used to check the formation of particular phases. Scanning electron microscope technique was used to study the surface morphology of the samples. The samples were studied in a temperature range of 298 K to 623 K and frequency range of 10 KHz to 1 MHz. The dielectric constant (εr), loss tangent (tan δ), and AC conductivity (σAC) were measured on sintered disks of BST samples. The DC resistivity of different compositions was measured at room temperature. Detailed studies of dielectric and electrical properties showed that these properties are strongly dependent on composition, frequency and temperature. The compounds showed stable behavior in lower temperature range (up to 523 K), therefore, they can be used in practical applications in this temperature range.

Keywords

  • barium samarium titanate (BST)
  • dielectric constant (εr)
  • loss tangent (tanδ)
  • AC conductivity (σAC)
  • DC resistivity
Open Access

Transformation mechanism of magnetite nanoparticles

Published Online: 11 Jul 2015
Page range: 278 - 285

Abstract

Abstract

A simple oxidation synthesis route was developed for producing magnetite nanoparticles with controlled size and morphology. Investigation of oxidation process of the produced magnetite nanoparticles (NP) was performed after synthesis under different temperatures. The phase transformation of synthetic magnetite nanoparticles into maghemite and, henceforth, to hematite nanoparticles at different temperatures under dry oxidation has been studied. The natural magnetite particles were directly transformed to hematite particles at comparatively lower temperature, thus, maghemite phase was bypassed. The phase structures, morphologies and particle sizes of the produced magnetic nanoparticles have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX) and BET surface area analysis.

Keywords

  • transformation
  • magnetite
  • maghemite
  • hematite
  • nanoparticles
Open Access

A density functional theory study of Raman modes of cadmium hexathiohypodiphosphate (CdPS3)

Published Online: 11 Jul 2015
Page range: 286 - 291

Abstract

Abstract

Raman scattering investigations based on density functional theory (DFT) calculations were performed to explore the vibrational modes of a cadmium hexathiohypodiphosphate CdPS3 single crystal. The calculations were performed to obtain the Raman spectra for the cadmium hexathiohypodiphosphate atoms to study the size dependence. Several vibrational modes indicating stretching and bending features related to Cd, S and P atoms were observed. Modifications of the frequency and intensity of different Raman modes with an increase in the number of atoms in CdPS3 were discussed in detail. Hydrogen atoms were added in order to make the closed shell configuration and saturate the CdPS3 as per the requisite for calculating the Raman spectra. This produced some additional modes of vibration related to hydrogen atoms. Band gap and formation energy were also calculated. The results generated are found to be in close agreement with the experimental values.

Keywords

  • CdPS3
  • vibrational modes
  • Raman
  • density functional theory (DFT)
Open Access

Synthesis and modification of reduced graphene oxide aerogels for biofuel cell applications

Published Online: 11 Jul 2015
Page range: 292 - 300

Abstract

Abstract

We have carried out the preparation of reduced graphene oxide aerogels using eco-friendly method that is based on the Hummers method of graphite oxidation without the use of NaNO3 that produces toxic gases. To obtain a porous 3D structure of reduced graphene oxide, we performed the hydrothermal reduction at elevated temperature. We also prepared the rGO aerogel/CNT composite using multiwalled carbon nanotubes as linkers. The rGO aerogels are promising materials as they possess good electrical conductivity (up to 100 S/m) and high surface area and porous structure (~500 m2/g). The main goal was to obtain the material for electrodes in enzymatic biofuel cells. Thus, the proper modification was performed using free radical functionalization. It was shown that in order to synthesize rGO aerogels modified with anthracene, the proper order of reactions needs to be provided. The morphology of anthracene modified electrodes was analyzed using scanning electron microscopy, which confirmed their porous structure with non-uniform pore size distribution that ranged between few nanometers to microns. Data obtained by Raman spectroscopy confirmed the successful oxidation and reduction of analyzed materials. UV-Vis spectra revealed the presence of anthracene moieties in examined materials. We also recorded preliminary cyclic voltammograms that confirm an electric conductivity of the obtained structures.

Keywords

  • graphene oxide
  • reduced graphene oxide
  • graphene aerogel
  • functionalization of graphene
  • biofuel cell
Open Access

Hydrothermal synthesis and characterization of polycrystalline gadolinium aluminum perovskite (GdAlO3, GAP)

Published Online: 11 Jul 2015
Page range: 301 - 305

Abstract

Abstract

Gadolinium aluminum perovskite (GdAlO3, GAP) is a promising high temperature ceramic material, known for its wide applications in phosphors. Polycrystalline gadolinium aluminum perovskites were synthesized using a precursor of co-precipitate gel of GdAlO3 by employing hydrothermal supercritical fluid technique under pressure and temperature ranging from 150 to 200 MPa and 600 to 700 °C, respectively. The resulted products of GAP were studied using the characterization techniques, such as powder X-ray diffraction analysis (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX). The X-ray diffraction pattern matched well with the reported orthorhombic GAP pattern (JCPDS-46-0395).

Keywords

  • perovskite
  • hydrothermal process
  • co-precipitated gel
  • supercritical temperature
Open Access

Morphology of polyamide 6 confined into carbon nanotubes

Published Online: 11 Jul 2015
Page range: 306 - 311

Abstract

Abstract

The preparation of polymer nanocomposites filled with carbon nanotubes requires the nanotubes to be uniformly dispersed and compatible with the polymer matrix. In this work we report a preparation method of polyamide 6 (PA 6) based nanocomposite containing multi-walled carbon nanotubes (MWCNT) without any additional surface modification and obtained by in situ polymerization, as a simple method for composites production. The process was assisted by ultrasounds prior to synthesis.With such a method, an interesting morphology of polyamide 6 confined into a multiwalled carbon nanotube as well as grafted on a carbon nanotube surface was observed. For comparative purpose, PA 6 nanocomposites were also prepared from commercially available master batch by melt compounding.

Keywords

  • polyamide 6
  • carbon nanotubes
  • in situ polymerization
  • nanocomposites
Open Access

Solvothermal synthesis and magnetic properties of β-Co2P nanorods

Published Online: 11 Jul 2015
Page range: 312 - 316

Abstract

Abstract

Hexagonal high temperature phase β-Co2P nanorods with a diameter of around 50 nm were synthesized via a mild solvothermal route. The reaction was carried out at 180 °C using cobalt chloride hexahydrate (CoCl2 · 6H2O) as Co source and yellow phosphorous as P source. The composition, structure as well as morphology were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM). The magnetic susceptibility curve indicates that the β-Co2P nanorods show canted antiferromagnetic state, different from the paramagnetic state of orthorhombic low temperature phase β-Co2P.

Keywords

  • solvothermal synthesis
  • magnetic materials
  • intermetallic alloys and compounds
  • nanocrystalline materials
Open Access

Effect of Ag on Sn–Cu and Sn–Zn lead free solders

Published Online: 11 Jul 2015
Page range: 317 - 330

Abstract

Abstract

Lead and lead-containing compounds are considered as toxic substances due to their detrimental effect on the environment. Sn-based soldering systems, like Sn-Cu and Sn-Zn are considered as the most promising candidates to replace the eutectic Sn-Pb solder compared to other solders because of their low melting temperature and favorable properties. Eutectic Sn-0.7 wt.% Cu and near eutectic composition Sn-8 wt.% Zn solders have been considered here for study. For the Sn-Cu system, besides the eutectic Sn-0.7 wt.% Cu composition, Sn-1Cu and Sn-2Cu were studied. Three compositions containing Ag: Sn-2Ag-0.7Cu, Sn-2.5Ag-0.7Cu and Sn-4.5Ag-0.7Cu were also developed. Ag was added to the eutectic Sn-0.7 wt.% Cu composition in order to reduce the melting temperature of the eutectic alloy and to enhance the mechanical properties. For the Sn-Zn system, besides the Sn-8 wt.% Zn near eutectic composition, Sn-8Zn-0.05Ag, Sn-8Zn-0.1Ag and Sn-8Zn-0.2Ag solder alloys were developed. The structure and morphology of the solder alloys were analyzed using a scanning electron microscope (SEM), filed emission scanning electron microscope (FESEM), electron diffraction X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Thermal analysis of the alloys was also done using a differential scanning calorimeter (DSC). Trace additions of Ag have been found to significantly reduce the melting temperature of the Sn-0.7 wt.% Cu and Sn-8 wt.% Zn alloys.

Keywords

  • Sn-Cu
  • Sn-Zn
  • Sn-Cu-Ag
  • Sn-Zn-Ag
  • eutectic alloys
  • thermal analysis
Open Access

Luminescence properties of novel red-emitting phosphor InNb1-xPxO4:Eu3+ for white light emitting-diodes

Published Online: 11 Jul 2015
Page range: 331 - 334

Abstract

Abstract

InNb1-xPxO4:Eu3+ red phosphors were synthesized by solid-state reaction and their luminescence properties were also studied through photoluminescence spectra. The excitation and emission spectra make it clear that the as-prepared phosphors can be effectively excited by near-ultraviolet (UV) 394 nm light and blue 466 nm light to emit strong red light located at 612 nm, due to the Eu3+ transition of 5D07F2. The luminescence intensity is dependent on phosphorus content, and it achieves the maximum at x = 0.4. Excessive phosphorus in the phosphors can result in reduction of luminescence intensity owing to concentration quenching.With the increasing content of phosphorus, the phosphors are prone to emit pure red light. This shows that the InNb1.6P0.4O4:0.04Eu3+ phosphor may be a potential candidate as a red component for white light emitting-diodes.

Keyowrds

  • solid-state reaction
  • phosphor
  • InNbO4
  • LEDs
Open Access

Investigation of microwave and electrical characteristics of Co–Zr substituted M-type Ba–Sr hexagonal ferrite

Published Online: 11 Jul 2015
Page range: 335 - 339

Abstract

Abstract

Microwave characteristics of M-type hexagonal ferrite, Ba0.5Sr0.5CoxZrxFe(12-2x)O19 (x = 0.0 to 1.0 in steps of 0.2), have been investigated as a function of frequency and substitution at X-band. The microwave absorption has been investigated using absorber testing device method. The static I-V characteristics have been studied as a function of substitution. The results show maximum microwave absorption at higher substitution. The static current exhibits ohmic behavior from 0 to 3 V and exponential trend from 3 to 4.8 V. The microstructure influences both microwave and electrical properties. The ferrite compositions for different electromagnetic applications are also suggested by measuring the microwave absorbed, transmitted and reflected power.

Keywords

  • ferrites
  • microwave properties
  • electrical properties
Open Access

Young’s modulus and creep compliance of GaAs and Ga1-xMnxAs ferromagnetic thin films under thermal stress at varied manganese doping levels

Published Online: 11 Jul 2015
Page range: 340 - 347

Abstract

Abstract

Dynamical mechanical analysis yields information about the mechanical properties of a material as a function of deforming factors, such as temperature, oscillating stress and strain amplitudes. GaAs and Mn-doped GaAs at varied levels, used in making electronic devices, suffer from damage due to changes in environmental temperatures. This is a defective factor experienced during winter and summer seasons. Hence, there was a need to establish the best amount of manganese to be doped in GaAs so as to obtain a mechanically stable spin injector material to make electronic devices. Mechanical properties of Ga1-xMnxAs spin injector were studied in relation to temperatures above room temperature (25 °C). Here, creep compliance, Young’s moduli and creep recovery for all studied samples with different manganese doping levels (MDLs) were determined using DMA 2980 Instrument from TA instruments Inc. The study was conducted using displace-recover programme on DMA creep mode with a single cantilever clamp. The samples were prepared using RF sputtering techniques. From the creep compliance study it was found that MDL of 10 % was appropriate at 30 °C and 40 °C. The data obtained can be useful to the spintronic and electronic device engineers in designing the appropriate devices to use at 30 °C and above or equal to 40 °C.

Keywords

  • creep compliance
  • Young’s modulus
  • percentage creep recovery
  • strain jumps
  • manganese doping levels
Open Access

Numerical model of the nanoindentation test based on the digital material representation of the Ti/TiN multilayers

Published Online: 11 Jul 2015
Page range: 348 - 355

Abstract

Abstract

The developed numerical model of a local nanoindentation test, based on the digital material representation (DMR) concept, has been presented within the paper. First, an efficient algorithm describing the pulsed laser deposition (PLD) process was proposed to realistically recreate the specific morphology of a nanolayered material in an explicit manner. The nanolayered Ti/TiN composite was selected for the investigation. Details of the developed cellular automata model of the PLD process were presented and discussed. Then, the Ti/TiN DMR was incorporated into the finite element software and numerical model of the nanoindentation test was established. Finally, examples of obtained results presenting capabilities of the proposed approach were highlighted.

Keywords

  • pulsed laser deposition
  • nanolayers
  • nanoindentation
  • digital material representation
Open Access

Research on high-temperature compression and creep behavior of porous Cu–Ni–Cr alloy for molten carbonate fuel cell anodes

Published Online: 11 Jul 2015
Page range: 356 - 362

Abstract

Abstract

The effect of porosity on high temperature compression and creep behavior of porous Cu alloy for the new molten carbonate fuel cell anodes was examined. Optical microscopy and scanning electron microscopy were used to investigate and analyze the details of the microstructure and surface deformation. Compression creep tests were utilized to evaluate the mechanical properties of the alloy at 650 °C. The compression strength, elastic modulus, and yield stress all increased with the decrease in porosity. Under the same creep stress, the materials with higher porosity exhibited inferior creep resistance and higher steadystate creep rate. The creep behavior has been classified in terms of two stages. The first stage relates to grain rearrangement which results from the destruction of large pores by the applied load. In the second stage, small pores are collapsed by a subsequent sintering process under the load. The main deformation mechanism consists in that several deformation bands generate sequentially under the perpendicular loading, and in these deformation bands the pores are deformed by flattering and collapsing sequentially. On the other hand, the shape of a pore has a severe influence on the creep resistance of the material, i.e. every increase of pore size corresponds to a decrease in creep resistance.

Keywords

  • porous Cu-Ni-Cr alloy
  • high temperature
  • compression behavior
  • creep behavior
Open Access

Investigations of electrical and optical properties of functional TCO thin films

Published Online: 11 Jul 2015
Page range: 363 - 368

Abstract

Abstract

Transparent conducting oxide (TCO) films of indium-tin-oxide were evaporated on the surface of silicon wafers after phosphorous diffusion and on the reference glass substrates. The influence of deposition process parameters (electron beam current, oxygen flow and the substrate temperature) on optical and electrical properties of evaporated thin films were investigated by means of resistivity measurements and optical spectrophotometry. The performance of prepared thin films was judged by calculated figure of merit and the best result was obtained for the sample deposited on the substrate heated to the 100 °C and then removed from the deposition chamber and annealed in an air for 5 minutes at 400 °C. Refractive index and extinction coefficient were evaluated based on measured transmission spectra and used for designing of antireflection coating for solar cell. The obtained results showed that prepared TCO thin films are promising as a part of counter electrode in crystalline silicon solar cell construction.

Keywords

  • transparent conducting oxide
  • crystalline silicon solar cell
  • transparent counter electrode
Open Access

A theoretical study on 2-chloro-5-(2-hydroxyethyl)-4-methoxy-6-methylpyrimidine by DFT/ab initio calculations

Published Online: 11 Jul 2015
Page range: 369 - 380

Abstract

Abstract

Quantum chemical calculations have been performed to study the molecular geometry, 1H and 13C NMR chemical shifts, conformational, natural bond orbital (NBO) and nonlinear optical (NLO) properties of the 2-chloro-5-(2-hydroxyethyl)-4- methoxy-6-methylpyrimidine molecule in the ground state using DFT and HF methods with 6-311++G(d,p) basis set. The optimized geometric parameters and 1H and 13C NMR chemical shifts have been compared with the experimental values of the title molecule. The results of the calculations show excellent agreement between the experimental and calculated frequencies at B3LYP/6-311++G(d,p) level. In order to provide a full understanding of the properties of the title molecule in the context of molecular orbital picture, the highest occupied molecular energy level (EHOMO), the lowest unoccupied molecular energy level (ELUMO), the energy difference (DE) between EHOMO and ELUMO, electronegativity (χ), hardness (η) and softness (S) have been calculated using B3LYP/6-311++G(d,p) and HF/6-311++G(d,p) levels. The calculated HOMO and LUMO energies show that the charge transfer occurs within the title molecule.

Keywords

  • 2-chloro-5-(2-hydroxyethyl)-4-methoxy-6-methylpyrimidine
  • HF and DFT
  • NMR
  • NBO
  • NLO
Open Access

Catalyst free growth of single-crystalline bismuth nanorods by closed space sublimation technique

Published Online: 11 Jul 2015
Page range: 381 - 390

Abstract

Abstract

In the present study, bismuth (Bi) thin films having thickness of 335 nm have been deposited onto a glass substrate by closed space sublimation (CSS) technique. Besides this, spontaneous growth of Bi nanorods has also been investigated for the first time, without template and catalyst assistance in a substrate temperature range of 380 to 430 °C using CSS technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to investigate microstructure, morphology and roughness of the Bi nanorods. The diameter and length ranges of Bi nanorods were 80 to 400 nm and 3 to 5 μm, respectively. Moreover, they exhibited a rhombohedral structure with a dominant peak indexed at (012), (104), and (110). The mass percentage of Bi, determined by energy dispersive X-ray (EDX), was 99.93 %. The studies of electrical resistivity, Hall coefficient, magnetoresistivity, hole mobility and carrier concentration of Bi thin films were performed at 300 to 350 K and the electrical properties were found to be a function of temperature. The basic aim was to investigate the spectacular evolution of Bi nanostructures on as-deposited thin films and effects of thickness on their structural, electrical and dielectric properties. Detailed examination of SEM micrographs eliminated all other growth modes except self-catalytic tip growth by Vapor-Solid (VS) growth process which is believed to provide the driving force for spontaneous nanorod growth at high substrate temperature. Deposition of thinner Bi films provided a new possibility for fabrication of Bi nanorods of high quality.

Keywords

  • crystallite size
  • bismuth
  • thin films
  • nanorods
  • substrate temperature
  • template
  • closed space sublimation
Open Access

Simulation of the thermo-optic coupling effect in mid-infrared second harmonic generation of ZnGeP2 crystal

Published Online: 11 Jul 2015
Page range: 391 - 396

Abstract

Abstract

The thermo-optic coupling process of second harmonic generation was numerically simulated in ZnGeP2 crystals pumped by a pulsed CO2 laser at the wavelength of 9.6 μm, under the strong and weak cooling conditions. The conversion efficiencies, temperature distributions were calculated during the evolution of the thermo-optic coupling. The results showed that the thermooptic coupling was weak in the strong cooling condition, which nearly did not disturb the conversion processes and temperature distribution, while in the weak cooling case, the temperature distribution showed a great influence on the conversion efficiency and light intensity. Finally, it was found that compensation of the phase mismatch induced by the thermal effect can well recover the conversion efficiency.

Keywords

  • second harmonic generation
  • thermo-optic coupling
  • ZnGeP2 crystal
Open Access

Electrochemical synthesis of nanoplatelets-like CuS0.2Se0.8 thin film for photoluminescence applications

Published Online: 11 Jul 2015
Page range: 397 - 401

Abstract

Abstract

Copper sulfide-selenide (CuS0.2Se0.8) thin films were deposited on FTO coated glass substrate (fluorine doped tin oxide) and stainless steel substrates using electrodeposition technique. Deposited thin films were characterized using different characterization techniques viz. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, photoluminescence spectroscopy and surface wettability. XRD study showed polycrystalline nature with cubic phase of the films. Scanning electron microscopy showed that the surface area of the substrate was covered by the nanoplatelets structure of a thickness of 140 to 150 nm and optical study showed that the direct band gap was ~1.90 eV. Surface wettability showed hydrophobic nature of the CuS0.2Se0.8 thin films.

Keywords

  • CuS0.2Se0.8 thin film
  • nanoplatelets
  • electrodeposition
  • photoluminescence (PL)
Open Access

Predictive study of structural, electronic, magnetic and thermodynamic properties of XFeO3 (X = Ag, Zr and Ru) multiferroic materials in cubic perovskite structure: first-principles calculations

Published Online: 11 Jul 2015
Page range: 402 - 413

Abstract

Abstract

The full potential linear-muffin-tin-orbital method within the spin local density approximation has been used to study the structural, electronic, magnetic and thermodynamic properties of three multiferroic compounds of XFeO3 type. Large values of bulk modulus for these compounds have been obtained, which demonstrates their hardness. The calculated total and partial density of states of these compounds shows a complex of strong hybridized 3d and 4d states at Fermi level. The two degenerate levels eg and t2g clearly demonstrate the origin of this complex. We have also investigated the effect of pressure, from 0 GPa to 55 GPa, on the magnetic moment per atom and the exchange of magnetic energy between the ferromagnetic and antiferromagnetic states. For more detailed knowledge, we have calculated the thermodynamic properties, and determined heat capacity, Debye temperature, bulk modulus and enthropy at different temperatures and pressures for the three multiferroic compounds. This is the first predictive calculation of all these properties.

Keywords

  • ab-initio
  • structural
  • electronic
  • magnetic
  • thermodynamic properties
Open Access

Effect of Ba addition on the structural, dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 ceramics

Published Online: 11 Jul 2015
Page range: 414 - 417

Abstract

Abstract

Lead-free (Na0.5Bi0.5)1-xBaxTiO3 (x = 0, 0.04 and 0.06) ceramics were fabricated by conventional solid phase sintering process. X-ray diffraction analysis shows that obtained specimens possess the perovskite structure. The microstructure study shows a dense structure, in good agreement with the relative density determined by the Archimedes method (above 95 %). Electric permittivity anomaly is shifted to low temperature after Ba doping of NBT. The pyroelectric and hysteresis loops measurements show that polarization and coercive field increases and decreases, respectively, after Ba doping of NBT. The obtained results are discussed in terms of ions/lattice imperfections, which create local electromechanical fields. The investigated ceramics are considered to be promising candidates for lead-free electronic materials.

Keywords

  • (Na0.5Bi0.5)1-xBaxTiO3
  • structural properties
  • ferroelectric properties
Open Access

Dielectric properties and molecular motions of liquid crystal molecules in 4-(2-methylbytyl)phenyl 4-(4-octylphenyl)benzoate liquid crystal having blue phase (CE8)

Published Online: 11 Jul 2015
Page range: 418 - 429

Abstract

Abstract

Blue phase liquid crystals exhibit unique properties which are used in the new type of display. A blue-phase liquid crystal display was first presented commercially by Samsung in 2007. The blue-phase-three-color pixel display eliminates the need for color filters. This type of display uses blue-phase multi-component liquid crystal. Considering the one-component systems, it turns out that they are stable only in a very narrow range of temperatures between the isotropic and the chiral nematic phase (about 1 K). In 2005, a wide temperature range BP multi-component system was reported by researchers from the University of Cambridge. There are still several unsolved problems left. One of them is chemical stability and reliability. Therefore, the knowledge of molecular dynamics of blue phase liquid crystal is a prerequisite for understanding of blue-phase multi-component system. Understanding the molecular dynamics of a single component liquid-crystalline blue phase system can facilitate the solution of these problems. We present the molecular dynamics investigation of 4-(2-methylbytyl)phenyl 4-(4-octylphenyl)benzoate (CE8), which may be a good candidate to form materials suitable for blue-phase liquid crystal displays.

Keywords

  • liquid crystal
  • blue phase
  • molecular dynamics
  • dielectric spectroscopy
  • correlation factor
Open Access

Two-extremum electrostatic potential of metal-lattice plasma and the work function of an electron

Published Online: 11 Jul 2015
Page range: 430 - 444

Abstract

Abstract

Metal-lattice plasma is treated as a neutral two-component two-phase system of 2D surface and 3D bulk. Free electron density and bulk chemical potential are used as intensive parameters of the system with the phase boundary position determined in the crystalline lattice. A semiempirical expression for the electron screened electrostatic potential is constructed using the lattice-plasma polarization concept. It comprises an image term and three repulsion/attraction terms of second and fourth orders. The novel curve has two extremes and agrees with certain theoretical forms of potential. A practical formula for the electron work function of metals and a simplified schema of electronic structure at the metal/vacuum interface are proposed. This yields 10.44 eV for the Fermi energy of free electron gas; -5.817 eV for the Fermi energy level; 4.509 eV for the average work function of bcc tungsten. Selected data are also given for fcc Cu and hcp Re. For harmonic frequencies ~ 10E16 per s of the self-excited metal-lattice plasma, energy gaps of 14.54 and 8.02 eV are found, which correspond to the bulk and surface plasmons, respectively. Further extension of this thermodynamics and metal-lattice theory based approach may contribute to a better understanding of theoretical models which are employed in chemical physics, catalysis and materials science of nanostructures.

Keywords

  • under-coordinated system
  • surface and interface
  • screened potential
  • metal-lattice plasma density
  • work function
  • electron affinity
Open Access

Growth of intermetallic compound between indium-based thermal interface material and copper substrate: molecular dynamics simulations

Published Online: 11 Jul 2015
Page range: 445 - 450

Abstract

Abstract

The diffusion phenomenon occurring between copper and indium was investigated by molecular dynamics simulations. The calculations were carried out in various temperatures in aging domain with the use of the commercially available Materials Studio v.6. software. The results showed that the intermetallic compound (IMC) growth followed the parabolic law, which indicated this growth to be mainly controlled by volume diffusion. The growth activation energy was estimated at 7.48 kJ · mol-1.

Keywords

  • thermal interface material (TIM)
  • molecular dynamics simulations (MD)
  • diffusivity
  • intermetallic compound (IMC)
29 Articles
Open Access

Grain growth kinetics for B2O3-doped ZnO ceramics

Published Online: 11 Jul 2015
Page range: 220 - 229

Abstract

Abstract

Grain growth kinetics in 0.1 to 2 mol % B2O3-added ZnO ceramics was studied by using a simplified phenomenological grain growth kinetics equation Gn = K0 · t · exp(-Q/RT) together with the physical properties of sintered samples. The samples, prepared by conventional ceramics processing techniques, were sintered at temperatures between 1050 to 1250 °C for 1, 2, 3, 5 and 10 hours in air. The kinetic grain growth exponent value (n) and the activation energy for the grain growth of the 0.1 mol % B2O3-doped ZnO ceramics were found to be 2.8 and 332 kJ/mol, respectively. By increasing B2O3 content to 1 mol %, the grain growth exponent value (n) and the activation energy decreased to 2 and 238 kJ/mol, respectively. The XRD study revealed the presence of a second phase, Zn3B2O6 formed when the B2O3 content was > 1 mol %. The formation of Zn3B2O6 phase gave rise to an increase of the grain growth kinetic exponent and the grain growth activation energy. The kinetic grain growth exponent value (n) and the activation energy for the grain growth of the 2 mol % B2O3-doped ZnO ceramics were found to be 3 and 307 kJ/mol, respectively. This can be attributed to the second particle drag (pinning) mechanism in the liquid phase sintering.

Keywords

  • boron oxide
  • grain growth
  • zinc oxide
Open Access

Synthesis and photocatalytic performance of spongy ZnO microstructures

Published Online: 11 Jul 2015
Page range: 230 - 236

Abstract

Abstract

Spongy ZnO microstructures were synthesized via a facile hydrothermal method using zinc nitrate hexahydrate and oxalic acid as raw materials. The as-obtained ZnO were characterized by powder X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and transmission electron spectroscopy (TEM), respectively. The BET surface area and average pore size of the samples were determined by nitrogen adsorption-desorption analysis. Effects of precursor and hydrothermal temperature on the morphology and photocatalytic activity of the products were investigated. SEM and TEM analysis indicated that the as-obtained spongy ZnO microstructures consisted of a large amount of ZnO particles with the average size of about 100 to 150 nm. The photocatalytic activities of the spongy ZnO microstructures were evaluated by photodegradation of methylene blue (MB) under UV light radiation. The results indicated that the ZnO synthesized at 150 °C for 10 h showed the highest photocatalytic activity and the degradation ratio of MB reached 99.5 % for 60 min of UV light irradiation with the light intensity of 10 mW · cm-2.

Keywords

  • ZnO
  • spongy structures
  • hydrothermal method
  • microstructures
Open Access

Improved efficiency of dye-sensitized solar cells by doping of strontium aluminate phosphor in TiO2 photoelectrode

Published Online: 11 Jul 2015
Page range: 237 - 241

Abstract

Abstract

SrAl2O4:Eu2+, Dy3+ phosphor was synthesized by chemical solution route to use as a dopant in TiO2 layer employed as a photoelectrode for down conversion of ultraviolet and near-ultraviolet to visible and near-infrared light in a dye-sensitized solar cell. Nano-crystalline structure of the SrAl2O4:Eu2+, Dy3+ powder was confirmed by X-ray diffraction analysis and field emission scanning electron microscopy. Monitored at 520 nm, SrAl2O4:Eu2+, Dy3+ phosphor showed emission peaks at 460 to 610 nm due to 4f6 4f7 transitions of Eu2+ ions. For the study, SrAl2O4:Eu2+, Dy3+ phosphor-doped TiO2 layer was deposited on fluorine-doped tin oxide coated glass by electrostatic spray deposition. The short circuit current, open circuit voltage, fill factor, and conversion efficiency of the cells were measured. Experimental results revealed that the device efficiency for the SrAl2O4:Eu2+, Dy3+ phosphor-doped TiO2 layer increased to 7.20 %, whereas that of the pure-TiO2 photoelectrode was 4.13 %.

Keywords

  • phosphor
  • down conversion
  • dye-sensitized solar cell
Open Access

Synthesis and electrical properties of silver nanoplates for electronic applications

Published Online: 11 Jul 2015
Page range: 242 - 250

Abstract

Abstract

In this paper, silver nanoplates of 100 to 500 nm size were synthesized by reduction of silver nitrate with N,Ndimethylformamide, using poly(vinylpyrolidone) as a surfactant and ferric chloride as a controlling agent, at 120 to 160 °C for 5 to 24 hours. The influence of the concentration of ferric chloride, the reaction temperature and reaction time on the morphology of the product has been investigated by transmission electron microscopy, scanning electron microscopy and UV-Vis spectroscopy. The results indicated that the products obtained at the low reaction temperature and short reaction time in the presence of FeCl3 in the reaction solution were in the form of silver nanoplates, whose morphology was mainly triangular and hexagonal. In addition, the size and thickness of the nanoplates increased with increasing of the FeCl3 concentration. At a high reaction temperature and long reaction time, the truncated triangle and hexagonal nanoplates were mainly produced. Furthermore, the sintering behavior of nanoplates was studied and the results showed that sintering of the silver nanoplates started at 180 °C, and a typical sintering behavior was observed at higher temperatures. The incorporation of the silver nanoplates into the polymer matrix with micro-sized silver flakes led to an increase in the matrix resistivity in almost all cases, especially at high fractions and low curing temperatures. The curing temperature had an influence on the resistivity of the conductive adhesives filled with micro-sized silver flakes and silver nanoplates due to sintering of the silver nanoplates.

Keywords

  • silver nanoplates
  • solvothermal process
  • controlling agent
  • sintering behavior
  • electrical properties
Open Access

First-principle investigations of structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides

Published Online: 11 Jul 2015
Page range: 251 - 258

Abstract

Abstract

In the present work, we have investigated the structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides in the B2 structure, using first-principle calculations of the density functional theory (DFT) based on the linearized augmented plane wave method (FP-LAPW) as implemented in the WIEN2k code, in which the energy of exchange and correlation are treated by the generalized gradient approximation (GGA), proposed in 1996 by Perdew, Burke and Ernzerhof (PBE). The ground state properties have been calculated and compared with other calculations, and the electronic structures of all FeAl, CoAl, and NiAl compounds exhibited a metallic behavior. It was depicted that the density of states is characterized by the large hybridization between the s-p (Al) and 3d (Fe, Co, and Ni) states, which creates the pseudogap in the region of anti-bonding states. Moreover, the band structures of FeAl, CoAl, and NiAl are similar to each other and the difference between them is in the energy level of each band relative to the Fermi level.

Keywords

  • first-principle calculations
  • intermetallics
  • electronic structures
Open Access

Frequency and temperature dependent transport properties of NiCuZn ceramic oxide

Published Online: 11 Jul 2015
Page range: 259 - 267

Abstract

Abstract

A polycrystalline sample of ceramic oxide Ni0.27Cu0.10Zn0.63Fe2O4 was prepared by the solid state reaction method. The sintered sample was well polished to remove any oxide layer formed during sintering and the two surfaces of the pellet were coated with a silver paste as a contact material. Among dielectric properties, complex dielectric constant (ε* = εʹ - jεʺ), loss tangent (tanδ) and ac conductivity (σac) in the frequency range of 20 Hz to 2 MHz were analyzed in the temperature range of 303 to 498 K using a Wayne Kerr impedance analyzer (model No. 6500B). The experimental results indicate that ε, εʺ, tanδ and σac decrease with an increase in frequency and increase with increasing temperature. The transition temperature, as obtained from dispersion curve of εʹ, shifts towards higher temperature with an increase in frequency. The variation of dielectric properties with frequency and temperature shows the dispersion behavior which is explained in the light of Maxwell-Wagner type of interfacial polarization in accordance with the Koop’s phenomenological theory. The frequency dependent conductivity results satisfy the Jonscher’s power law, σT(ω) = σ(o)+Aωn, and the results show the occurrence of two types of conduction process at elevated temperature: (i) low frequency conductivity, due to long-range ordering (frequency independent, region I), (ii) mid frequency conductivity at the grain boundaries (region II, dispersion) and (iii) high frequency conductivity at the grain interior due to the short-range hopping mechanism (frequency independent plateau, region III).

Keywords

  • NiCuZn ferrite
  • dielectric properties
  • ac conductivity
  • frequency and temperature dependence
Open Access

Frequency and temperature dependence of dielectric and electric properties of Ba2-xSm4+2x/3Ti8O24 with structural analysis

Published Online: 11 Jul 2015
Page range: 268 - 277

Abstract

Abstract

Dielectric ceramics samples of barium titanium oxide doped with samarium, having a complex structural formula of Ba2-xSm4+2x/3Ti8O24 (referred to as BST), were fabricated by a high temperature solid-state reaction technique with varying x (0.0, 0.2, 0.4, 0.6). X-ray diffraction technique was used to check the formation of particular phases. Scanning electron microscope technique was used to study the surface morphology of the samples. The samples were studied in a temperature range of 298 K to 623 K and frequency range of 10 KHz to 1 MHz. The dielectric constant (εr), loss tangent (tan δ), and AC conductivity (σAC) were measured on sintered disks of BST samples. The DC resistivity of different compositions was measured at room temperature. Detailed studies of dielectric and electrical properties showed that these properties are strongly dependent on composition, frequency and temperature. The compounds showed stable behavior in lower temperature range (up to 523 K), therefore, they can be used in practical applications in this temperature range.

Keywords

  • barium samarium titanate (BST)
  • dielectric constant (εr)
  • loss tangent (tanδ)
  • AC conductivity (σAC)
  • DC resistivity
Open Access

Transformation mechanism of magnetite nanoparticles

Published Online: 11 Jul 2015
Page range: 278 - 285

Abstract

Abstract

A simple oxidation synthesis route was developed for producing magnetite nanoparticles with controlled size and morphology. Investigation of oxidation process of the produced magnetite nanoparticles (NP) was performed after synthesis under different temperatures. The phase transformation of synthetic magnetite nanoparticles into maghemite and, henceforth, to hematite nanoparticles at different temperatures under dry oxidation has been studied. The natural magnetite particles were directly transformed to hematite particles at comparatively lower temperature, thus, maghemite phase was bypassed. The phase structures, morphologies and particle sizes of the produced magnetic nanoparticles have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX) and BET surface area analysis.

Keywords

  • transformation
  • magnetite
  • maghemite
  • hematite
  • nanoparticles
Open Access

A density functional theory study of Raman modes of cadmium hexathiohypodiphosphate (CdPS3)

Published Online: 11 Jul 2015
Page range: 286 - 291

Abstract

Abstract

Raman scattering investigations based on density functional theory (DFT) calculations were performed to explore the vibrational modes of a cadmium hexathiohypodiphosphate CdPS3 single crystal. The calculations were performed to obtain the Raman spectra for the cadmium hexathiohypodiphosphate atoms to study the size dependence. Several vibrational modes indicating stretching and bending features related to Cd, S and P atoms were observed. Modifications of the frequency and intensity of different Raman modes with an increase in the number of atoms in CdPS3 were discussed in detail. Hydrogen atoms were added in order to make the closed shell configuration and saturate the CdPS3 as per the requisite for calculating the Raman spectra. This produced some additional modes of vibration related to hydrogen atoms. Band gap and formation energy were also calculated. The results generated are found to be in close agreement with the experimental values.

Keywords

  • CdPS3
  • vibrational modes
  • Raman
  • density functional theory (DFT)
Open Access

Synthesis and modification of reduced graphene oxide aerogels for biofuel cell applications

Published Online: 11 Jul 2015
Page range: 292 - 300

Abstract

Abstract

We have carried out the preparation of reduced graphene oxide aerogels using eco-friendly method that is based on the Hummers method of graphite oxidation without the use of NaNO3 that produces toxic gases. To obtain a porous 3D structure of reduced graphene oxide, we performed the hydrothermal reduction at elevated temperature. We also prepared the rGO aerogel/CNT composite using multiwalled carbon nanotubes as linkers. The rGO aerogels are promising materials as they possess good electrical conductivity (up to 100 S/m) and high surface area and porous structure (~500 m2/g). The main goal was to obtain the material for electrodes in enzymatic biofuel cells. Thus, the proper modification was performed using free radical functionalization. It was shown that in order to synthesize rGO aerogels modified with anthracene, the proper order of reactions needs to be provided. The morphology of anthracene modified electrodes was analyzed using scanning electron microscopy, which confirmed their porous structure with non-uniform pore size distribution that ranged between few nanometers to microns. Data obtained by Raman spectroscopy confirmed the successful oxidation and reduction of analyzed materials. UV-Vis spectra revealed the presence of anthracene moieties in examined materials. We also recorded preliminary cyclic voltammograms that confirm an electric conductivity of the obtained structures.

Keywords

  • graphene oxide
  • reduced graphene oxide
  • graphene aerogel
  • functionalization of graphene
  • biofuel cell
Open Access

Hydrothermal synthesis and characterization of polycrystalline gadolinium aluminum perovskite (GdAlO3, GAP)

Published Online: 11 Jul 2015
Page range: 301 - 305

Abstract

Abstract

Gadolinium aluminum perovskite (GdAlO3, GAP) is a promising high temperature ceramic material, known for its wide applications in phosphors. Polycrystalline gadolinium aluminum perovskites were synthesized using a precursor of co-precipitate gel of GdAlO3 by employing hydrothermal supercritical fluid technique under pressure and temperature ranging from 150 to 200 MPa and 600 to 700 °C, respectively. The resulted products of GAP were studied using the characterization techniques, such as powder X-ray diffraction analysis (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX). The X-ray diffraction pattern matched well with the reported orthorhombic GAP pattern (JCPDS-46-0395).

Keywords

  • perovskite
  • hydrothermal process
  • co-precipitated gel
  • supercritical temperature
Open Access

Morphology of polyamide 6 confined into carbon nanotubes

Published Online: 11 Jul 2015
Page range: 306 - 311

Abstract

Abstract

The preparation of polymer nanocomposites filled with carbon nanotubes requires the nanotubes to be uniformly dispersed and compatible with the polymer matrix. In this work we report a preparation method of polyamide 6 (PA 6) based nanocomposite containing multi-walled carbon nanotubes (MWCNT) without any additional surface modification and obtained by in situ polymerization, as a simple method for composites production. The process was assisted by ultrasounds prior to synthesis.With such a method, an interesting morphology of polyamide 6 confined into a multiwalled carbon nanotube as well as grafted on a carbon nanotube surface was observed. For comparative purpose, PA 6 nanocomposites were also prepared from commercially available master batch by melt compounding.

Keywords

  • polyamide 6
  • carbon nanotubes
  • in situ polymerization
  • nanocomposites
Open Access

Solvothermal synthesis and magnetic properties of β-Co2P nanorods

Published Online: 11 Jul 2015
Page range: 312 - 316

Abstract

Abstract

Hexagonal high temperature phase β-Co2P nanorods with a diameter of around 50 nm were synthesized via a mild solvothermal route. The reaction was carried out at 180 °C using cobalt chloride hexahydrate (CoCl2 · 6H2O) as Co source and yellow phosphorous as P source. The composition, structure as well as morphology were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM). The magnetic susceptibility curve indicates that the β-Co2P nanorods show canted antiferromagnetic state, different from the paramagnetic state of orthorhombic low temperature phase β-Co2P.

Keywords

  • solvothermal synthesis
  • magnetic materials
  • intermetallic alloys and compounds
  • nanocrystalline materials
Open Access

Effect of Ag on Sn–Cu and Sn–Zn lead free solders

Published Online: 11 Jul 2015
Page range: 317 - 330

Abstract

Abstract

Lead and lead-containing compounds are considered as toxic substances due to their detrimental effect on the environment. Sn-based soldering systems, like Sn-Cu and Sn-Zn are considered as the most promising candidates to replace the eutectic Sn-Pb solder compared to other solders because of their low melting temperature and favorable properties. Eutectic Sn-0.7 wt.% Cu and near eutectic composition Sn-8 wt.% Zn solders have been considered here for study. For the Sn-Cu system, besides the eutectic Sn-0.7 wt.% Cu composition, Sn-1Cu and Sn-2Cu were studied. Three compositions containing Ag: Sn-2Ag-0.7Cu, Sn-2.5Ag-0.7Cu and Sn-4.5Ag-0.7Cu were also developed. Ag was added to the eutectic Sn-0.7 wt.% Cu composition in order to reduce the melting temperature of the eutectic alloy and to enhance the mechanical properties. For the Sn-Zn system, besides the Sn-8 wt.% Zn near eutectic composition, Sn-8Zn-0.05Ag, Sn-8Zn-0.1Ag and Sn-8Zn-0.2Ag solder alloys were developed. The structure and morphology of the solder alloys were analyzed using a scanning electron microscope (SEM), filed emission scanning electron microscope (FESEM), electron diffraction X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Thermal analysis of the alloys was also done using a differential scanning calorimeter (DSC). Trace additions of Ag have been found to significantly reduce the melting temperature of the Sn-0.7 wt.% Cu and Sn-8 wt.% Zn alloys.

Keywords

  • Sn-Cu
  • Sn-Zn
  • Sn-Cu-Ag
  • Sn-Zn-Ag
  • eutectic alloys
  • thermal analysis
Open Access

Luminescence properties of novel red-emitting phosphor InNb1-xPxO4:Eu3+ for white light emitting-diodes

Published Online: 11 Jul 2015
Page range: 331 - 334

Abstract

Abstract

InNb1-xPxO4:Eu3+ red phosphors were synthesized by solid-state reaction and their luminescence properties were also studied through photoluminescence spectra. The excitation and emission spectra make it clear that the as-prepared phosphors can be effectively excited by near-ultraviolet (UV) 394 nm light and blue 466 nm light to emit strong red light located at 612 nm, due to the Eu3+ transition of 5D07F2. The luminescence intensity is dependent on phosphorus content, and it achieves the maximum at x = 0.4. Excessive phosphorus in the phosphors can result in reduction of luminescence intensity owing to concentration quenching.With the increasing content of phosphorus, the phosphors are prone to emit pure red light. This shows that the InNb1.6P0.4O4:0.04Eu3+ phosphor may be a potential candidate as a red component for white light emitting-diodes.

Keyowrds

  • solid-state reaction
  • phosphor
  • InNbO4
  • LEDs
Open Access

Investigation of microwave and electrical characteristics of Co–Zr substituted M-type Ba–Sr hexagonal ferrite

Published Online: 11 Jul 2015
Page range: 335 - 339

Abstract

Abstract

Microwave characteristics of M-type hexagonal ferrite, Ba0.5Sr0.5CoxZrxFe(12-2x)O19 (x = 0.0 to 1.0 in steps of 0.2), have been investigated as a function of frequency and substitution at X-band. The microwave absorption has been investigated using absorber testing device method. The static I-V characteristics have been studied as a function of substitution. The results show maximum microwave absorption at higher substitution. The static current exhibits ohmic behavior from 0 to 3 V and exponential trend from 3 to 4.8 V. The microstructure influences both microwave and electrical properties. The ferrite compositions for different electromagnetic applications are also suggested by measuring the microwave absorbed, transmitted and reflected power.

Keywords

  • ferrites
  • microwave properties
  • electrical properties
Open Access

Young’s modulus and creep compliance of GaAs and Ga1-xMnxAs ferromagnetic thin films under thermal stress at varied manganese doping levels

Published Online: 11 Jul 2015
Page range: 340 - 347

Abstract

Abstract

Dynamical mechanical analysis yields information about the mechanical properties of a material as a function of deforming factors, such as temperature, oscillating stress and strain amplitudes. GaAs and Mn-doped GaAs at varied levels, used in making electronic devices, suffer from damage due to changes in environmental temperatures. This is a defective factor experienced during winter and summer seasons. Hence, there was a need to establish the best amount of manganese to be doped in GaAs so as to obtain a mechanically stable spin injector material to make electronic devices. Mechanical properties of Ga1-xMnxAs spin injector were studied in relation to temperatures above room temperature (25 °C). Here, creep compliance, Young’s moduli and creep recovery for all studied samples with different manganese doping levels (MDLs) were determined using DMA 2980 Instrument from TA instruments Inc. The study was conducted using displace-recover programme on DMA creep mode with a single cantilever clamp. The samples were prepared using RF sputtering techniques. From the creep compliance study it was found that MDL of 10 % was appropriate at 30 °C and 40 °C. The data obtained can be useful to the spintronic and electronic device engineers in designing the appropriate devices to use at 30 °C and above or equal to 40 °C.

Keywords

  • creep compliance
  • Young’s modulus
  • percentage creep recovery
  • strain jumps
  • manganese doping levels
Open Access

Numerical model of the nanoindentation test based on the digital material representation of the Ti/TiN multilayers

Published Online: 11 Jul 2015
Page range: 348 - 355

Abstract

Abstract

The developed numerical model of a local nanoindentation test, based on the digital material representation (DMR) concept, has been presented within the paper. First, an efficient algorithm describing the pulsed laser deposition (PLD) process was proposed to realistically recreate the specific morphology of a nanolayered material in an explicit manner. The nanolayered Ti/TiN composite was selected for the investigation. Details of the developed cellular automata model of the PLD process were presented and discussed. Then, the Ti/TiN DMR was incorporated into the finite element software and numerical model of the nanoindentation test was established. Finally, examples of obtained results presenting capabilities of the proposed approach were highlighted.

Keywords

  • pulsed laser deposition
  • nanolayers
  • nanoindentation
  • digital material representation
Open Access

Research on high-temperature compression and creep behavior of porous Cu–Ni–Cr alloy for molten carbonate fuel cell anodes

Published Online: 11 Jul 2015
Page range: 356 - 362

Abstract

Abstract

The effect of porosity on high temperature compression and creep behavior of porous Cu alloy for the new molten carbonate fuel cell anodes was examined. Optical microscopy and scanning electron microscopy were used to investigate and analyze the details of the microstructure and surface deformation. Compression creep tests were utilized to evaluate the mechanical properties of the alloy at 650 °C. The compression strength, elastic modulus, and yield stress all increased with the decrease in porosity. Under the same creep stress, the materials with higher porosity exhibited inferior creep resistance and higher steadystate creep rate. The creep behavior has been classified in terms of two stages. The first stage relates to grain rearrangement which results from the destruction of large pores by the applied load. In the second stage, small pores are collapsed by a subsequent sintering process under the load. The main deformation mechanism consists in that several deformation bands generate sequentially under the perpendicular loading, and in these deformation bands the pores are deformed by flattering and collapsing sequentially. On the other hand, the shape of a pore has a severe influence on the creep resistance of the material, i.e. every increase of pore size corresponds to a decrease in creep resistance.

Keywords

  • porous Cu-Ni-Cr alloy
  • high temperature
  • compression behavior
  • creep behavior
Open Access

Investigations of electrical and optical properties of functional TCO thin films

Published Online: 11 Jul 2015
Page range: 363 - 368

Abstract

Abstract

Transparent conducting oxide (TCO) films of indium-tin-oxide were evaporated on the surface of silicon wafers after phosphorous diffusion and on the reference glass substrates. The influence of deposition process parameters (electron beam current, oxygen flow and the substrate temperature) on optical and electrical properties of evaporated thin films were investigated by means of resistivity measurements and optical spectrophotometry. The performance of prepared thin films was judged by calculated figure of merit and the best result was obtained for the sample deposited on the substrate heated to the 100 °C and then removed from the deposition chamber and annealed in an air for 5 minutes at 400 °C. Refractive index and extinction coefficient were evaluated based on measured transmission spectra and used for designing of antireflection coating for solar cell. The obtained results showed that prepared TCO thin films are promising as a part of counter electrode in crystalline silicon solar cell construction.

Keywords

  • transparent conducting oxide
  • crystalline silicon solar cell
  • transparent counter electrode
Open Access

A theoretical study on 2-chloro-5-(2-hydroxyethyl)-4-methoxy-6-methylpyrimidine by DFT/ab initio calculations

Published Online: 11 Jul 2015
Page range: 369 - 380

Abstract

Abstract

Quantum chemical calculations have been performed to study the molecular geometry, 1H and 13C NMR chemical shifts, conformational, natural bond orbital (NBO) and nonlinear optical (NLO) properties of the 2-chloro-5-(2-hydroxyethyl)-4- methoxy-6-methylpyrimidine molecule in the ground state using DFT and HF methods with 6-311++G(d,p) basis set. The optimized geometric parameters and 1H and 13C NMR chemical shifts have been compared with the experimental values of the title molecule. The results of the calculations show excellent agreement between the experimental and calculated frequencies at B3LYP/6-311++G(d,p) level. In order to provide a full understanding of the properties of the title molecule in the context of molecular orbital picture, the highest occupied molecular energy level (EHOMO), the lowest unoccupied molecular energy level (ELUMO), the energy difference (DE) between EHOMO and ELUMO, electronegativity (χ), hardness (η) and softness (S) have been calculated using B3LYP/6-311++G(d,p) and HF/6-311++G(d,p) levels. The calculated HOMO and LUMO energies show that the charge transfer occurs within the title molecule.

Keywords

  • 2-chloro-5-(2-hydroxyethyl)-4-methoxy-6-methylpyrimidine
  • HF and DFT
  • NMR
  • NBO
  • NLO
Open Access

Catalyst free growth of single-crystalline bismuth nanorods by closed space sublimation technique

Published Online: 11 Jul 2015
Page range: 381 - 390

Abstract

Abstract

In the present study, bismuth (Bi) thin films having thickness of 335 nm have been deposited onto a glass substrate by closed space sublimation (CSS) technique. Besides this, spontaneous growth of Bi nanorods has also been investigated for the first time, without template and catalyst assistance in a substrate temperature range of 380 to 430 °C using CSS technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to investigate microstructure, morphology and roughness of the Bi nanorods. The diameter and length ranges of Bi nanorods were 80 to 400 nm and 3 to 5 μm, respectively. Moreover, they exhibited a rhombohedral structure with a dominant peak indexed at (012), (104), and (110). The mass percentage of Bi, determined by energy dispersive X-ray (EDX), was 99.93 %. The studies of electrical resistivity, Hall coefficient, magnetoresistivity, hole mobility and carrier concentration of Bi thin films were performed at 300 to 350 K and the electrical properties were found to be a function of temperature. The basic aim was to investigate the spectacular evolution of Bi nanostructures on as-deposited thin films and effects of thickness on their structural, electrical and dielectric properties. Detailed examination of SEM micrographs eliminated all other growth modes except self-catalytic tip growth by Vapor-Solid (VS) growth process which is believed to provide the driving force for spontaneous nanorod growth at high substrate temperature. Deposition of thinner Bi films provided a new possibility for fabrication of Bi nanorods of high quality.

Keywords

  • crystallite size
  • bismuth
  • thin films
  • nanorods
  • substrate temperature
  • template
  • closed space sublimation
Open Access

Simulation of the thermo-optic coupling effect in mid-infrared second harmonic generation of ZnGeP2 crystal

Published Online: 11 Jul 2015
Page range: 391 - 396

Abstract

Abstract

The thermo-optic coupling process of second harmonic generation was numerically simulated in ZnGeP2 crystals pumped by a pulsed CO2 laser at the wavelength of 9.6 μm, under the strong and weak cooling conditions. The conversion efficiencies, temperature distributions were calculated during the evolution of the thermo-optic coupling. The results showed that the thermooptic coupling was weak in the strong cooling condition, which nearly did not disturb the conversion processes and temperature distribution, while in the weak cooling case, the temperature distribution showed a great influence on the conversion efficiency and light intensity. Finally, it was found that compensation of the phase mismatch induced by the thermal effect can well recover the conversion efficiency.

Keywords

  • second harmonic generation
  • thermo-optic coupling
  • ZnGeP2 crystal
Open Access

Electrochemical synthesis of nanoplatelets-like CuS0.2Se0.8 thin film for photoluminescence applications

Published Online: 11 Jul 2015
Page range: 397 - 401

Abstract

Abstract

Copper sulfide-selenide (CuS0.2Se0.8) thin films were deposited on FTO coated glass substrate (fluorine doped tin oxide) and stainless steel substrates using electrodeposition technique. Deposited thin films were characterized using different characterization techniques viz. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, photoluminescence spectroscopy and surface wettability. XRD study showed polycrystalline nature with cubic phase of the films. Scanning electron microscopy showed that the surface area of the substrate was covered by the nanoplatelets structure of a thickness of 140 to 150 nm and optical study showed that the direct band gap was ~1.90 eV. Surface wettability showed hydrophobic nature of the CuS0.2Se0.8 thin films.

Keywords

  • CuS0.2Se0.8 thin film
  • nanoplatelets
  • electrodeposition
  • photoluminescence (PL)
Open Access

Predictive study of structural, electronic, magnetic and thermodynamic properties of XFeO3 (X = Ag, Zr and Ru) multiferroic materials in cubic perovskite structure: first-principles calculations

Published Online: 11 Jul 2015
Page range: 402 - 413

Abstract

Abstract

The full potential linear-muffin-tin-orbital method within the spin local density approximation has been used to study the structural, electronic, magnetic and thermodynamic properties of three multiferroic compounds of XFeO3 type. Large values of bulk modulus for these compounds have been obtained, which demonstrates their hardness. The calculated total and partial density of states of these compounds shows a complex of strong hybridized 3d and 4d states at Fermi level. The two degenerate levels eg and t2g clearly demonstrate the origin of this complex. We have also investigated the effect of pressure, from 0 GPa to 55 GPa, on the magnetic moment per atom and the exchange of magnetic energy between the ferromagnetic and antiferromagnetic states. For more detailed knowledge, we have calculated the thermodynamic properties, and determined heat capacity, Debye temperature, bulk modulus and enthropy at different temperatures and pressures for the three multiferroic compounds. This is the first predictive calculation of all these properties.

Keywords

  • ab-initio
  • structural
  • electronic
  • magnetic
  • thermodynamic properties
Open Access

Effect of Ba addition on the structural, dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 ceramics

Published Online: 11 Jul 2015
Page range: 414 - 417

Abstract

Abstract

Lead-free (Na0.5Bi0.5)1-xBaxTiO3 (x = 0, 0.04 and 0.06) ceramics were fabricated by conventional solid phase sintering process. X-ray diffraction analysis shows that obtained specimens possess the perovskite structure. The microstructure study shows a dense structure, in good agreement with the relative density determined by the Archimedes method (above 95 %). Electric permittivity anomaly is shifted to low temperature after Ba doping of NBT. The pyroelectric and hysteresis loops measurements show that polarization and coercive field increases and decreases, respectively, after Ba doping of NBT. The obtained results are discussed in terms of ions/lattice imperfections, which create local electromechanical fields. The investigated ceramics are considered to be promising candidates for lead-free electronic materials.

Keywords

  • (Na0.5Bi0.5)1-xBaxTiO3
  • structural properties
  • ferroelectric properties
Open Access

Dielectric properties and molecular motions of liquid crystal molecules in 4-(2-methylbytyl)phenyl 4-(4-octylphenyl)benzoate liquid crystal having blue phase (CE8)

Published Online: 11 Jul 2015
Page range: 418 - 429

Abstract

Abstract

Blue phase liquid crystals exhibit unique properties which are used in the new type of display. A blue-phase liquid crystal display was first presented commercially by Samsung in 2007. The blue-phase-three-color pixel display eliminates the need for color filters. This type of display uses blue-phase multi-component liquid crystal. Considering the one-component systems, it turns out that they are stable only in a very narrow range of temperatures between the isotropic and the chiral nematic phase (about 1 K). In 2005, a wide temperature range BP multi-component system was reported by researchers from the University of Cambridge. There are still several unsolved problems left. One of them is chemical stability and reliability. Therefore, the knowledge of molecular dynamics of blue phase liquid crystal is a prerequisite for understanding of blue-phase multi-component system. Understanding the molecular dynamics of a single component liquid-crystalline blue phase system can facilitate the solution of these problems. We present the molecular dynamics investigation of 4-(2-methylbytyl)phenyl 4-(4-octylphenyl)benzoate (CE8), which may be a good candidate to form materials suitable for blue-phase liquid crystal displays.

Keywords

  • liquid crystal
  • blue phase
  • molecular dynamics
  • dielectric spectroscopy
  • correlation factor
Open Access

Two-extremum electrostatic potential of metal-lattice plasma and the work function of an electron

Published Online: 11 Jul 2015
Page range: 430 - 444

Abstract

Abstract

Metal-lattice plasma is treated as a neutral two-component two-phase system of 2D surface and 3D bulk. Free electron density and bulk chemical potential are used as intensive parameters of the system with the phase boundary position determined in the crystalline lattice. A semiempirical expression for the electron screened electrostatic potential is constructed using the lattice-plasma polarization concept. It comprises an image term and three repulsion/attraction terms of second and fourth orders. The novel curve has two extremes and agrees with certain theoretical forms of potential. A practical formula for the electron work function of metals and a simplified schema of electronic structure at the metal/vacuum interface are proposed. This yields 10.44 eV for the Fermi energy of free electron gas; -5.817 eV for the Fermi energy level; 4.509 eV for the average work function of bcc tungsten. Selected data are also given for fcc Cu and hcp Re. For harmonic frequencies ~ 10E16 per s of the self-excited metal-lattice plasma, energy gaps of 14.54 and 8.02 eV are found, which correspond to the bulk and surface plasmons, respectively. Further extension of this thermodynamics and metal-lattice theory based approach may contribute to a better understanding of theoretical models which are employed in chemical physics, catalysis and materials science of nanostructures.

Keywords

  • under-coordinated system
  • surface and interface
  • screened potential
  • metal-lattice plasma density
  • work function
  • electron affinity
Open Access

Growth of intermetallic compound between indium-based thermal interface material and copper substrate: molecular dynamics simulations

Published Online: 11 Jul 2015
Page range: 445 - 450

Abstract

Abstract

The diffusion phenomenon occurring between copper and indium was investigated by molecular dynamics simulations. The calculations were carried out in various temperatures in aging domain with the use of the commercially available Materials Studio v.6. software. The results showed that the intermetallic compound (IMC) growth followed the parabolic law, which indicated this growth to be mainly controlled by volume diffusion. The growth activation energy was estimated at 7.48 kJ · mol-1.

Keywords

  • thermal interface material (TIM)
  • molecular dynamics simulations (MD)
  • diffusivity
  • intermetallic compound (IMC)

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