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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 35 (2017): Issue 2 (July 2017)

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

Search

23 Articles
access type Open Access

Gas-sensing properties and in-situ diffuse-reflectance Fourier-transform infrared spectroscopy study of diethyl ether adsorption and reactions on SnO2 film

Published Online: 26 Jul 2017
Page range: 265 - 274

Abstract

Abstract

Diethyl ether is a common industrial reagent and medical anesthetic. It is necessary to carry out real-time monitoring of this molecule due to its harmful effects on human health. In this paper, a highly sensitive diethyl ether SnO2 gas-sensing material has been prepared by a sol-gel method. The gas sensitivity was tested by a home-made gas-sensing equipment. The surface adsorption and reaction processes between the SnO2 gas-sensing film and the diethyl ether have been studied by in situ diffuse-reflectance Fourier-transform infrared spectroscopy (DRFT-IR) at different temperatures. The results show that the SnO2 gas-sensing material has high sensitivity to diethyl ether, and the lowest detection limit can reach 1 ppm. Furthermore, ethyl (CH3CH2●), oxoethyl (CH3CH2O●), ethanol (CH3CH2OH), formaldehyde (HCHO), acetaldehyde (CH3CHO), ethylene (C2H4), H2O and CO2 surface species are formed during diethyl ether adsorption at different temperatures. A possible mechanism of the reaction process is discussed.

Keywords

  • gas sensitivity
  • SnO2 film
  • diethyl ether
  • in situ DRFT-IR
access type Open Access

CeO2/NiTiO3 nanocomposites; synthesis, photoluminescence and magnetic behavior

Published Online: 26 Jul 2017
Page range: 275 - 282

Abstract

Abstract

Pure phase NiTiO3 was obtained via a modified sol-gel method. Addition of CeO2 in a modified oxidizing atmosphere in stearic acid at 750 °C led to the growth of several nanoscaled Ce-rich phases. The formation of NiTiO3 and CeO2/NiTiO3 was strongly confirmed based on metal-oxygen and metal-metal absorption bands. The nanometric formation of crystals and narrow distribution of nanoparticles were confirmed by XRD and FE-SEM. The magnetic properties indicated weak ferromagnetic behavior of NiTiO3 and paramagnetic behavior of CeO2/NiTiO3 nanocomposites. The paramagnetic properties were improved gradually into superparamagnetic upon increasing CeO2 domain to 30 mol%. It was observed that the current density can achieve 1 × 10-9 A/cm2 for the sample containing 30 mol% CeO2 at an electrical field equal to 40 V/cm.

Keywords

  • NiTiO3
  • sol-gel
  • magnetic behavior
  • nanocomposite
access type Open Access

Structural, electronic and magnetic properties of Fe, Co, Ni monatomic nanochains encapsulated in armchair LiF nanotubes

Published Online: 26 Jul 2017
Page range: 283 - 290

Abstract

Abstract

Structural, electronic and magnetic properties of transition metal TM (TM = Fe, Co and Ni) atomic chains wrapped in single walled LiF armchair nanotubes have been investigated by the first-principles calculations in the framework of the density functional theory. The generalized gradient approximation (GGA) with Hubbard repulsion potential and without Hubbard repulsion was employed to describe the exchange-correlation potential. It is found that all these TM chains @LiFNTs systems have negative formation energy so they are stable and exothermic. Total density of states and partial densities of states analyses show that the spin polarization and the magnetic moment of TM chains @LiFNTs(n,n) systems come mostly from the TM atom chains. All these nanocomposites are ferromagnetic (FM) and spin splitting between spin up and down is observed. The high magnetic moment and spin polarization of the TM chains @LiFNT(n,n) systems show that they can be used as magnetic nanostructures possessing potential current and future applications in permanent magnetism, magnetic recording, and spintronics.

Keywords

  • LiF nanotube
  • DFT
  • encapsulated nanochains
  • transition metals
  • Hubbard repulsion
access type Open Access

Properties of thin ZnS:Mn films sprayed by improved method: The role of Mn2+ ion concentration

Published Online: 26 Jul 2017
Page range: 291 - 302

Abstract

Abstract

Undoped and Mn-doped thin ZnS films were deposited on ordinary glass substrates at temperature of 450 °C by an improved spray pyrolysis (ISP) method. The ISP parameters, such as carrier gas flow rate, solution flow rate and substrate temperature, were controlled with accuracy ±0.25 Lpm, ±1 mL/h and ±1 °C, respectively. A pulse-spray mode of the method was used to spray the precursor solution. Thin film samples were prepared for Mn-doping with the concentrations of 0 at.%, 1 at.%, 3 at.%, 6 at.%, 8 at.% and 12 at.% relative to Zn in the spray solution. The Mn-doping concentration dependent chemical composition, surface morphology, and structural, optical and photoluminescence (PL) properties were studied. All the thin films were well adherent, nearly stoichiometric, dense, uniform, and possessed cubic crystal structure with preferential orientation along h〈1 1 1〉 direction. A slight enhancement in structural properties, an increase in band gap, and a decrease in refractive index and dielectric constant with Mn-doping concentration were observed. The PL spectra of Mn-doped thin ZnS films at room temperature exhibited both the 490 nm blue defect-related emission and the 590 nm yellow-orange Mn2+ ion related emission. The observed yellow-orange emission intensity was maximum for 3 at.% of Mn-doping concentration in the spray solution.

Keywords

  • improved spray pyrolysis
  • pulse-spray mode
  • Mn-doped ZnS
  • Mn2+ ion concentration
  • photoluminescence
access type Open Access

Heat resisting and water-soluble chocolate polyesters containing azomethine group

Published Online: 26 Jul 2017
Page range: 303 - 312

Abstract

Abstract

In this study, soluble in water poly(azomethine-ester)s (PAEs) were synthesized via elimination reactions of aromatic dihydroxy compounds containing imine bonding with terephthaloyl chloride. The structures of Schiff bases (SBs) and PAEs containing different aliphatic chains were confirmed by FT-IR, 1H-NMR, 13C-NMR and UV-Vis analyses. Physicochemical properties of the new polymers were characterized. Thermal properties of the compounds were investigated by TGA-DTA, DMA and DSC. According to TGA measurements, the starting degradation temperatures (Ton) of P-1, P-2, P-3, and P-4 poly(azomethine-ester)s were found as 255 °C, 232 °C, 222 °C, and 221 °C, respectively. The starting degradation temperatures of the poly(azomethine-ester)s were higher than their Schiff base compounds. According to dynamical mechanical analysis (DMA) measurements, glass transition temperature (Tg) of P-1, P-2, P-3, and P-4 poly(azomethine-ester)s were found as 95 °C, 138 °C, 140 °C, and 145 °C, respectively. The morphological and topographic properties of the PAEs containing azomethine linkage in the main chain were investigated by FE-SEM and AFM, respectively. The molecular mass distributions of PAEs were determined by gel permeation chromatography (GPC). Electrochemical (E′g) and optical band gap (Eoptg ) values of the prepared SBs and PAEs were calculated from cyclic voltammetry (CV) and UV-Vis analyses. The electrochemical band gap (E′g) values of P-1, P-2, P-3 and P-4 were found as 2.44 eV, 2.41 eV, 2.39 eV and 2.39 eV, respectively, from the cyclic voltammetry.

Keywords

  • poly(azomethine-ester)
  • Schiff base
  • water-soluble
  • electrochemical properties
  • thermal degradation
  • elimination reactions
access type Open Access

Studies on structure, growth and characterization of third order nonlinear optical 2-amino-5-chloropyridinium-4-amino benzoate single crystal

Published Online: 26 Jul 2017
Page range: 313 - 321

Abstract

Abstract

Optically transparent single crystals of 2-amino-5-chloropyridinium-4-amino benzoate (2A5CP4AB) were grown at room temperature using solution growth technique. The structure was solved with a support of single crystal XRD, which revealed that the title compound belongs to the monoclinic crystal system having centrosymmetric space group P21/n. The UV-Vis spectrum and photoluminescence properties of the title compound showed the optical transmittance and emission behavior of the compound. The optical band gap was evaluated using the Tauc plot and it was found to be about 3.53 eV. The third order nonlinear optical behavior of the crystal was determined using Z-scan technique. Mechanical properties of the title compound were studied using Vickers microhardness study.

Keywords

  • solution growth
  • nonlinear optical properties
  • photoluminescence
access type Open Access

PbS nanopowder – synthesis, characterization and antimicrobial activity

Published Online: 26 Jul 2017
Page range: 322 - 328

Abstract

Abstract

Lead sulphide (PbS) nanopowder was synthesized by a simple soft chemical route using lead nitrate and thiourea as precursor salts. The as-synthesized nanopowder was characterized by XRD, SEM, EDX, FT-IR, PL, Raman and magnetic measurements. XRD studies reveal the polycrystalline nature of the powder. The powder exhibits face-centered cubic structure with a strong (2 0 0) preferential orientation. The presence of Pb and S in the powder is confirmed by energy dispersive X-ray analysis. The peaks observed at 1112 cm-1 and at 606 cm-1 in the FT-IR spectrum are related to heteropolar diatomic molecules of PbS. The Raman peak shift at 173 cm-1 might have originated from the combination of longitudinal and transverse acoustic phonon modes associated with PbS crystal. The M-H loop confirms the paramagnetic nature of the as-synthesized PbS nanopowder. The nanopowder has significant antimicrobial activity against certain bacteria and fungi strains which make it suitable as antimicrobial agent against pathogenic microorganisms.

Keywords

  • X-ray diffraction
  • photoluminescence
  • energy dispersive X-ray analysis
  • antimicrobial properties
access type Open Access

Effect of deposition temperature on structural, optical and electrical properties of copper bismuth sulphide (CuBiS2) thin films deposited by chemical bath deposition

Published Online: 26 Jul 2017
Page range: 329 - 334

Abstract

Abstract

The effect of deposition temperature on the structural, optical and electrical properties of copper bismuth sulphide (CuBiS2) thin films deposited by chemical bath deposition onto glass substrates at different deposition temperatures (40 °C, 50 °C, 60 °C and 70 °C) for 5 hours deposition time period was investigated. The obtained films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and optical absorption spectra. All deposited films were polycrystalline and had an orthorhombic structure. Their grain size had changed with deposition temperature and their compositions were nearly stoichiometric. The optical band gap value was decreased from 2.44 eV to 2.33 eV with increasing the film thickness. Electrical parameters such as mobility and type of electrical conduction were determined from the Hall effect measurements. They showed that the obtained films have n-type conductivity and mobility values of the copper bismuth sulphide (CuBiS2) films have changed with deposition temperature.

Keywords

  • copper bismuth sulphide (CuBiS2)
  • polycrystalline structure
  • X-ray technique
  • optical band gap
  • Hall coefficient
access type Open Access

Influence of annealing temperature on the structural and optical properties of As30Te70 thin films

Published Online: 26 Jul 2017
Page range: 335 - 345

Abstract

Abstract

Chalcogenide glasses have attracted much attention largely due to their interesting physical and chemical properties. Though few published articles exist on the As-Te system, little is known about the optical properties of eutectic or near eutectic composition of As-Te system upon heat treatment. Therefore, this paper reports the effects of annealing temperature on the structural and optical parameters of As30Te70 thin films. The bulk and thin films of 150 nm thick As30Te70 chalcogenide glasses were prepared by melt-quenching and thermal evaporation techniques, respectively. The glass transition and crystallization reactions of the bulk samples were investigated using differential scanning calorimetry (DSC). The influence of annealing temperature on the transformation of the crystal structure was studied by X-ray diffraction (XRD), while the surface morphology of the annealed samples was examined using scanning electron microscope (SEM). The optical band gap, refractive index and extinction coefficient were also calculated. The DSC scans showed that the melting temperature remains constant at 636.56 K. In addition, other characteristic temperatures such as the glass transition temperature, the onset crystallization temperature, and the crystallization peak temperature increase with increasing the heating rate. The crystalline phases for the as-prepared and annealed films consist of orthorhombic As, hexagonal Te, and monoclinic As2Te3 phases. Furthermore, the average crystallite size, strain, and dislocation density depend on the annealing temperature. The optical absorption results revealed that the investigated films have a direct transition, and their optical energy gap decreases from 1.82 eV to 1.49 eV as the annealing temperature increases up to 433 K. However, the refractive index, extinction coefficient, dielectric constant and the ratio of free carrier concentration to its effective mass, increase with increasing the annealing temperature.

Keywords

  • chalcogenide glasses
  • As-Te system
  • thin films
  • structural
  • optical parameters
  • thermal evaporation
access type Open Access

Excitability of high-energy ultraviolet radiation for Dy3+ in antimony phosphate glasses

Published Online: 26 Jul 2017
Page range: 346 - 354

Abstract

Abstract

Dy3+ doped antimony phosphate (ZASP) glasses are synthesized and the specificity of the luminescence behavior is demonstrated. Different from the conventional long-wave ultraviolet (UVA) exciting cases, the excitable area of Dy3+ doped ZASP glasses is extended to high-energy ultraviolet radiation including medium-wave ultraviolet (UVB) and short-wave ultraviolet (UVC) spectral regions. The quantum efficiency for 4F9/2 level of Dy3+ in low- and medium-concentration Dy2O3 doping cases reaches 95.0 % and 66.7 %, respectively, confirming the emission effectiveness from Dy3+ in ZASP glasses. The values of energy-transfer probability (P) have obvious difference while using 340 nm and 540 nm as monitoring wavelengths, so asthe energy-transfer efficiencies (η), which are related to the energy-transfer processes from discrepant Sb3+ donors to Dy3+ acceptors, were in-equivalent. The effective excitability of high-energy ultraviolet radiation illustrates that Dy3+ doped ZASP glasses are a promising candidate in developing visible light sources, display devices and tunable visible lasers.

Keywords

  • Dy3+
  • antimony phosphate glasses
  • excitability of high-energy ultraviolet radiation
  • energy transfer
access type Open Access

Optical and structural properties of nanostructured copper oxide thin films as solar selective coating prepared by spray pyrolysis method

Published Online: 26 Jul 2017
Page range: 355 - 361

Abstract

Abstract

Copper (II) oxide thin films were prepared by spray pyrolysis method on soda-lime glass substrates using copper acetate precursor solution. Influence of substrate temperature on structural and optical properties was investigated. Structural analysis of these layers were carried out by X-ray diffraction (XRD). Single phase nature and high crystallinity of CuO nanostructures were observed on XRD patterns. The general appearance of the films was uniform and black in color. FT-IR transmittance spectra confirmed the results from the XRD study. Selective solar absorber coatings of copper oxide (CuO) on stainless steel substrates was prepared by spray pyrolysis method. Effect of deposition temperature on optical properties of thin films was investigated. Optical parameters, absorbance (α) and emittance (α) were evaluated from reflectance data. It can be deduced that the porous structure, such as a light traps, can greatly enhance absorbance, while the composition, thickness and roughness of thin films can greatly influence the emissivity. Single phase nature and high crystallinity of CuO nanostructures were observed by XRD patterns. Solar absorbance of thin films were in the range of 85 % to 92 %.

Keywords

  • spray pyrolysis
  • solar selective absorber
  • optical parameters
access type Open Access

Phase evolution and microwave dielectric properties of A5M5O17-type ceramics

Published Online: 26 Jul 2017
Page range: 362 - 367

Abstract

Abstract

A number of A5M5O17 (A = Na, Ca, Sr, La, Nd, Sm, Gd, Dy, Yb; B = Ti, Nb, Ta) type compounds were prepared by a solid-state sintering route and characterized in terms of structure, microstructure and microwave dielectric properties. The compatibility of rare earths with mixed niobate/tantalate and titanate phases was investigated. The larger ionic radii mismatch resulted in the formation of pyrochlore and/or mixed phases while in other cases, pure A5M5O17 phase was formed. The samples exhibited relative permittivity in the range of 35 to 82, quality factor (Q × fo) = 897 GHz to 11946 GHz and temperature coefficient of resonance frequency (τf) = -120 ppm/°C to 318 ppm/°C.

Keywords

  • A5M5O17
  • dielectrics
  • microwave properties
access type Open Access

Kinetic properties and structural analysis of LaCrO3 nanoparticles

Published Online: 26 Jul 2017
Page range: 368 - 373

Abstract

Abstract

LaCrO3 perovskite nanopowders were successfully prepared via a sol-gel method using stoichiometric proportion of materials containing lanthanum and chromium in stearic acid complexing agent. Structural analysis of LaCrO3 indicated an octahedral framework in its XRD pattern bearing crystallite size in the range of 28 nm. The particle sizes were confirmed by morphological scanning of the sample. The optical properties of LaCrO3 nanopowders clearly indicated an interesting optical activity of LaCrO3 in the UV and visible ranges. The degradation activation energy (Ed) was calculated from the output of a moderate thermal programming profile at about 207.97 kJ·mol-1 using Kissinger equation. Capacity, impedance and AC resistance of the perovskites was obtained at 2.970 nF, 2.522 MΩ and 16.19 MΩ, respectively.

Keywords

  • LaCrO3
  • nanoperovskite
  • sol-gel
  • kinetic parameter
access type Open Access

Al-doped ZnO films deposited by magnetron sputtering: effect of sputtering parameters on the electrical and optical properties

Published Online: 26 Jul 2017
Page range: 374 - 381

Abstract

Abstract

Aluminum-doped zinc oxide (AZO) thin films were prepared by magnetron sputtering method. The influences of deposition pressure, substrate temperature, Ar flow rate and film thickness on optical and electrical properties were investigated using ultraviolet-visible (UV-Vis) spectrometer and Hall measurements. The experimental results revealed that a low resistivity, smaller than 4 × 10-4 Ω·cm, was obtained when the deposition pressure was smaller than 0.67 Pa and substrate temperature about 200 °C. Ar flow rate had a small influence on the resistivity but a big influence on the transparency at near infrared range (NIR). We obtained optimized AZO thin films with high ponductivity and transparency at low deposition pressure, small Ar flow and appropriate temperature (around 200 °C). The etching behavior of the AZO thin films deposited at the different Ar flow rates was also studied in this paper. The results show that Ar flow rate is a very important factor affecting the etching behavior.

Keywords

  • AZO thin films
  • optical and electrical properties
  • morphology
access type Open Access

Enhanced thermal conductivity of graphene nanoplatelets epoxy composites

Published Online: 26 Jul 2017
Page range: 382 - 389

Abstract

Abstract

Efficient heat dissipation from modern electronic devices is a key issue for their proper performance. An important role in the assembly of electronic devices is played by polymers, due to their simple application and easiness of processing. The thermal conductivity of pure polymers is relatively low and addition of thermally conductive particles into polymer matrix is the method to enhance the overall thermal conductivity of the composite. The aim of the presented work is to examine a possibility of increasing the thermal conductivity of the filled epoxy resin systems, applicable for electrical insulation, by the use of composites filled with graphene nanoplatelets. It is remarkable that the addition of only 4 wt.% of graphene could lead to 132 % increase in thermal conductivity. In this study, several new aspects of graphene composites such as sedimentation effects or temperature dependence of thermal conductivity have been presented. The thermal conductivity results were also compared with the newest model. The obtained results show potential for application of the graphene nanocomposites for electrical insulation with enhanced thermal conductivity. This paper also presents and discusses the unique temperature dependencies of thermal conductivity in a wide temperature range, significant for full understanding thermal transport mechanisms.

Keywords

  • graphene nanoplatelets
  • thermal conductivity
  • electrical resistivity
  • epoxy resin
  • high-shear exfoliation
access type Open Access

Structural and luminescent properties of Fe3+ doped PVA capped CdTe nanoparticles

Published Online: 26 Jul 2017
Page range: 390 - 397

Abstract

Abstract

During recent decades, magnetic and semiconductor nanoparticles have attracted significant attention of scientists in various fields of engineering, physics, chemistry, biology and medicine. Fe3+ doped PVA capped CdTe nanoparticles were prepared by co-precipitation method and characterized by powder X-ray diffraction, SEM, TEM, FT-IR, optical, EPR and PL techniques to collect the information about the crystal structure, coordination/local site symmetry of doped Fe3+ ions in the host lattice and the luminescent properties of prepared sample. Powder XRD data revealed that the crystal structure belongs to a cubic system and its lattice cell parameters were evaluated. The average crystallite size was estimated to be 8 nm. The morphology of prepared samples was analyzed by using SEM and TEM investigations. Functional groups of the prepared sample were observed in FT-IR spectra. Optical absorption and EPR studies have shown that on doping, Fe3+ ions enter the host lattice in octahedral site symmetry. PL studies of Fe3+ doped PVA capped CdTe nanoparticles revealed UV and blue emission bands. CIE chromaticity coordinates were also calculated from the emission spectrum of Fe3+ doped PVA capped CdTe nanoparticles.

Keywords

  • CdTe
  • PVA
  • co-precipitation
  • iron ions
  • optical absorption
  • EPR
  • FT-IR
  • photoluminescence
access type Open Access

Modelling the power losses in the ferromagnetic materials

Published Online: 26 Jul 2017
Page range: 398 - 404

Abstract

Abstract

In this paper, the problem of describing power losses in ferromagnetic materials is considered. The limitations of Steinmetz formula are shown and a new analytical description of losses in a considered material is proposed. The correctness of the developed description is demonstrated experimentally by comparing the results of calculation with the catalogue characteristics for different ferromagnetic materials.

Keywords

  • ferromagnetic material
  • power loss
  • modelling
  • powder cores
  • ferrite cores
  • nanocrystalline cores
access type Open Access

Preparation and characterization of (Co0:3Zn0:7)(Ti1–xSnx)Nb2O8 microwave dielectric ceramics

Published Online: 26 Jul 2017
Page range: 405 - 411

Abstract

Abstract

Zn0.7Co0.3(Ti1-xSnx)Nb2O8 (x = 0.1, 0.15, 0.2, 0.25, 0.3, 0.35) microwave ceramics were prepared by traditional solidstate reaction method. The influences of Sn substituted for Ti on the phase constitution, crystal structure and microwave dielectric properties of Zn0.7Co0.3(Ti1-xSnx)Nb2O8 ceramics were discussed. The XRD patterns revealed the main phase of ZnTiNb2O8 and little content of Zn0.17Ti0.5Nb0.33O2 secondary phase. With further substitution of Sn, the lattice constant, volume and apparent density of the ceramics increased, the ceramic structure reached a maximal compactness at x = 0.2 which was shown on SEM. Tremendous improvement of Q × f and a declining trend of Ɛr and τf were obtained with increasing x value. Appropriate substitution value (x = 0.10) would ensure excellent microwave dielectric properties (Ɛr = 34.1, Q × f = 40562 GHz, τf =-5 ppm/°C) of the ceramics sintered at 1080 °C.

Keywords

  • microwave dielectric ceramics
  • (Co0.3Zn0.7)(Ti1-xSnx)Nb2O8
  • ixiolite structure
access type Open Access

Ga2O3 nanowires preparation at atmospheric pressure

Published Online: 26 Jul 2017
Page range: 412 - 420

Abstract

Abstract

An attempt has been undertaken to produce gallium oxide nanowires by thermal synthesis from metallic gallium source at atmospheric pressure. Silicon substrates of (1 0 0) and (1 1 1) orientation with and without silicon oxide layers (0.5 μm) were used as support. Evaporated thin gold films were deposited on the top of those silicon carriers as a catalytic agent. After thermal treatment by Rapid Thermal Processing RTP (at various temperatures and times), which was applied to make small Au islands with the diameters of about several tens of nanometers, the substrate surfaces were observed by SEM. The Ga2O3 syntheses were made at various conditions: time, temperature and gas mixture were changed. As a result, monoclinic gallium oxide β-Ga2O3 nanostructures with dominant [1 1 1] and [0 0 2] growth directions were grown. The obtained nanostructures of several tens micrometers length were studied by SEM, PL and X-ray methods.

Keywords

  • Ga2O3
  • nanowires
  • nanobelts
  • thermal synthesis
  • atmospheric pressure
access type Open Access

An impact of the copper additive on photocatalytic and bactericidal properties of TiO2 thin films

Published Online: 26 Jul 2017
Page range: 421 - 426

Abstract

Abstract

The biological and photocatalytic activity of TiO2 and TiO2:Cu in relation to their structure, surface topography, wettability and optical properties of the thin films was investigated. Thin-film coatings were prepared by magnetron sputtering method in oxygen plasma with use of metallic targets (Ti and Ti-Cu). The results of structural studies revealed that addition of Cu into titania matrix (during the deposition process) resulted in obtaining of an amorphous film, while in case of undoped TiO2, presence of nanocrystalline anatase (with crystallites size of 20 nm) was found. Moreover, an addition of cooper had also an effect on surface diversification and decrease of its hydrophilicity. The roughness of TiO2:Cu film was 25 % lower (0.6 nm) as-compared to titania (0.8 nm). These modifications of TiO2:Cu had an impact on the decrease of its photocatalytic activity, probably as a result of the active surface area decrease. Antibacterial and antifungal properties of the thin films against bacteria (Enterococcus hirae, Staphylococcus aureus, Bacillus subtilis, Escherichia coli) and yeast (Candida albicans) were also examined. For the purpose of this work the method dedicated for the evaluation of antimicrobial properties of thin films was developed. It was revealed that Cu-additive has a positive impact on neutralization of microorganisms.

Keywords

  • TiO2
  • thin film
  • microstructure
  • photocatalysis
  • bioactivity
  • optical properties
access type Open Access

Synthesis of Cu and Ce co-doped ZnO nanoparticles: crystallographic, optical, molecular, morphological and magnetic studies

Published Online: 26 Jul 2017
Page range: 427 - 434

Abstract

Abstract

In the present research work, crystallographic, optical, molecular, morphological and magnetic properties of Zn1-xCuxO (ZnCu) and Zn1-x-yCeyCuxO (ZnCeCu) nanoparticles have been investigated. Polyvinyl alcohol (PVA) coated ZnCu and ZnCeCu nanoparticles have been synthesized by chemical sol-gel method and thoroughly studied using various characterization techniques. X-ray diffraction pattern indicates the wurtzite structure of the synthesized ZnCu and ZnCeCu particles. Transmission electron microscopy analysis shows that the synthesized ZnCu and ZnCeCu particles are of spherical shape, having average sizes of 27 nm and 23 nm, respectively. The incorporation of Cu and Ce in the ZnO lattice has been confirmed through Fourier transform infrared spectroscopy. Room temperature photoluminescence spectra of the ZnO doped with Cu and co-doped Ce display two emission bands, predominant ultra-violet near-band edge emission at 409.9 nm (3 eV) and a weak green-yellow emission at 432.65 nm (2.27 eV). Room temperature magnetic study confirms the diamagnetic behavior of ZnCu and ferromagnetic behavior of ZnCeCu.

Keywords

  • copper and cerium co-doped ZnO
  • wurtzite structure
  • transmission electron microscope
  • magnetization
  • optical properties
access type Open Access

Influence of Bi3+ content on photoluminescence of InNbO4:Eu3+,Bi3+ for white light-emitting diodes

Published Online: 26 Jul 2017
Page range: 435 - 439

Abstract

Abstract

A series of red-emitting phosphors InNbO4:Eu3+,Bi3+ was prepared by a high temperature solid-state reaction. The structure, size distribution and luminescence properties of the phosphors were respectively characterized by X-ray diffraction (XRD), laser particle size and molecular fluorescence spectrometer. The XRD results indicate that the phase-pure samples have been obtained and the crystal structure of the host has not changed under the Eu3+ and Bi3+ co-doping. The test of size distribution shows that the phosphor has a normal size distribution. The excitation spectra illustrate that the dominant sharp peaks are located at 394 nm (7F05L6) and 466 nm (7F05D2). Meanwhile, the emission spectra reveal that the phosphors excited by the wavelength of 394 nm or 466 nm have an intense red-emission line at 612 nm owing to the 5D07F2 transition of Eu3+. Bi3+ doping has not changed the peak positions except the photoluminescence intensity. The emission intensity is related to Bi3+ concentration, and it is up to the maximum when the Bi3+-doping concentration is 4 mol%. Due to good photoluminescence properties of the phosphor, the InNbO4:0.04Eu3+,0.04Bi3+ may be used as a red component for white light-emitting diodes.

Keywords

  • red-emitting phosphor
  • photoluminescence properties
  • white LEDs
  • InNbO4
  • solid-state reaction
access type Open Access

Electrical transport and magnetoresistance of double layered CMR manganites R1.2Sr1.8Mn2O7(R = La, Pr, Sm)

Published Online: 26 Jul 2017
Page range: 440 - 446

Abstract

Abstract

Polycrystalline bulk samples of double layered (DL) colossal magnetoresistive (CMR) manganites R1.2Sr1.8Mn2O7 (R = La, Pr, Sm) were prepared by sol-gel method to study the effect of size of lanthanide ion on their magnetotransport properties. The electrical resistivity of the samples was investigated in the temperature range of 70 K to 300 K at different magnetic fields. The samples LSMO and PSMO show insulator-to-metal transition (IMT) behavior, while SSMO sample exhibits insulating behavior in the entire temperature range with a very large value of resistivity. The insulator-to-metal transition temperature (TIM) decreases from 123 K (LSMO) to 90 K (PSMO) and disappears in SSMO sample. To explain the electrical transport above TIM, the temperature dependent resistivity data (T > TIM) of all the samples were fitted to the equations of different conduction models. The results indicate that the conduction at T > TIM is due to Mott variable range hopping (VRH) mechanism in the LSMO and PSMO samples, while Efros-Shkloskii (ES) type of VRH model dominates the conduction process in the SSMO sample. All the three samples show increasing magnetoresistance (MR) even below TIM and the maximum MR is shown by LSMO (39 % at 75 K, 3 T).

Keywords

  • double layered manganites
  • electrical transport
  • magnetoresistance
  • variable range hopping
  • sol-gel process
23 Articles
access type Open Access

Gas-sensing properties and in-situ diffuse-reflectance Fourier-transform infrared spectroscopy study of diethyl ether adsorption and reactions on SnO2 film

Published Online: 26 Jul 2017
Page range: 265 - 274

Abstract

Abstract

Diethyl ether is a common industrial reagent and medical anesthetic. It is necessary to carry out real-time monitoring of this molecule due to its harmful effects on human health. In this paper, a highly sensitive diethyl ether SnO2 gas-sensing material has been prepared by a sol-gel method. The gas sensitivity was tested by a home-made gas-sensing equipment. The surface adsorption and reaction processes between the SnO2 gas-sensing film and the diethyl ether have been studied by in situ diffuse-reflectance Fourier-transform infrared spectroscopy (DRFT-IR) at different temperatures. The results show that the SnO2 gas-sensing material has high sensitivity to diethyl ether, and the lowest detection limit can reach 1 ppm. Furthermore, ethyl (CH3CH2●), oxoethyl (CH3CH2O●), ethanol (CH3CH2OH), formaldehyde (HCHO), acetaldehyde (CH3CHO), ethylene (C2H4), H2O and CO2 surface species are formed during diethyl ether adsorption at different temperatures. A possible mechanism of the reaction process is discussed.

Keywords

  • gas sensitivity
  • SnO2 film
  • diethyl ether
  • in situ DRFT-IR
access type Open Access

CeO2/NiTiO3 nanocomposites; synthesis, photoluminescence and magnetic behavior

Published Online: 26 Jul 2017
Page range: 275 - 282

Abstract

Abstract

Pure phase NiTiO3 was obtained via a modified sol-gel method. Addition of CeO2 in a modified oxidizing atmosphere in stearic acid at 750 °C led to the growth of several nanoscaled Ce-rich phases. The formation of NiTiO3 and CeO2/NiTiO3 was strongly confirmed based on metal-oxygen and metal-metal absorption bands. The nanometric formation of crystals and narrow distribution of nanoparticles were confirmed by XRD and FE-SEM. The magnetic properties indicated weak ferromagnetic behavior of NiTiO3 and paramagnetic behavior of CeO2/NiTiO3 nanocomposites. The paramagnetic properties were improved gradually into superparamagnetic upon increasing CeO2 domain to 30 mol%. It was observed that the current density can achieve 1 × 10-9 A/cm2 for the sample containing 30 mol% CeO2 at an electrical field equal to 40 V/cm.

Keywords

  • NiTiO3
  • sol-gel
  • magnetic behavior
  • nanocomposite
access type Open Access

Structural, electronic and magnetic properties of Fe, Co, Ni monatomic nanochains encapsulated in armchair LiF nanotubes

Published Online: 26 Jul 2017
Page range: 283 - 290

Abstract

Abstract

Structural, electronic and magnetic properties of transition metal TM (TM = Fe, Co and Ni) atomic chains wrapped in single walled LiF armchair nanotubes have been investigated by the first-principles calculations in the framework of the density functional theory. The generalized gradient approximation (GGA) with Hubbard repulsion potential and without Hubbard repulsion was employed to describe the exchange-correlation potential. It is found that all these TM chains @LiFNTs systems have negative formation energy so they are stable and exothermic. Total density of states and partial densities of states analyses show that the spin polarization and the magnetic moment of TM chains @LiFNTs(n,n) systems come mostly from the TM atom chains. All these nanocomposites are ferromagnetic (FM) and spin splitting between spin up and down is observed. The high magnetic moment and spin polarization of the TM chains @LiFNT(n,n) systems show that they can be used as magnetic nanostructures possessing potential current and future applications in permanent magnetism, magnetic recording, and spintronics.

Keywords

  • LiF nanotube
  • DFT
  • encapsulated nanochains
  • transition metals
  • Hubbard repulsion
access type Open Access

Properties of thin ZnS:Mn films sprayed by improved method: The role of Mn2+ ion concentration

Published Online: 26 Jul 2017
Page range: 291 - 302

Abstract

Abstract

Undoped and Mn-doped thin ZnS films were deposited on ordinary glass substrates at temperature of 450 °C by an improved spray pyrolysis (ISP) method. The ISP parameters, such as carrier gas flow rate, solution flow rate and substrate temperature, were controlled with accuracy ±0.25 Lpm, ±1 mL/h and ±1 °C, respectively. A pulse-spray mode of the method was used to spray the precursor solution. Thin film samples were prepared for Mn-doping with the concentrations of 0 at.%, 1 at.%, 3 at.%, 6 at.%, 8 at.% and 12 at.% relative to Zn in the spray solution. The Mn-doping concentration dependent chemical composition, surface morphology, and structural, optical and photoluminescence (PL) properties were studied. All the thin films were well adherent, nearly stoichiometric, dense, uniform, and possessed cubic crystal structure with preferential orientation along h〈1 1 1〉 direction. A slight enhancement in structural properties, an increase in band gap, and a decrease in refractive index and dielectric constant with Mn-doping concentration were observed. The PL spectra of Mn-doped thin ZnS films at room temperature exhibited both the 490 nm blue defect-related emission and the 590 nm yellow-orange Mn2+ ion related emission. The observed yellow-orange emission intensity was maximum for 3 at.% of Mn-doping concentration in the spray solution.

Keywords

  • improved spray pyrolysis
  • pulse-spray mode
  • Mn-doped ZnS
  • Mn2+ ion concentration
  • photoluminescence
access type Open Access

Heat resisting and water-soluble chocolate polyesters containing azomethine group

Published Online: 26 Jul 2017
Page range: 303 - 312

Abstract

Abstract

In this study, soluble in water poly(azomethine-ester)s (PAEs) were synthesized via elimination reactions of aromatic dihydroxy compounds containing imine bonding with terephthaloyl chloride. The structures of Schiff bases (SBs) and PAEs containing different aliphatic chains were confirmed by FT-IR, 1H-NMR, 13C-NMR and UV-Vis analyses. Physicochemical properties of the new polymers were characterized. Thermal properties of the compounds were investigated by TGA-DTA, DMA and DSC. According to TGA measurements, the starting degradation temperatures (Ton) of P-1, P-2, P-3, and P-4 poly(azomethine-ester)s were found as 255 °C, 232 °C, 222 °C, and 221 °C, respectively. The starting degradation temperatures of the poly(azomethine-ester)s were higher than their Schiff base compounds. According to dynamical mechanical analysis (DMA) measurements, glass transition temperature (Tg) of P-1, P-2, P-3, and P-4 poly(azomethine-ester)s were found as 95 °C, 138 °C, 140 °C, and 145 °C, respectively. The morphological and topographic properties of the PAEs containing azomethine linkage in the main chain were investigated by FE-SEM and AFM, respectively. The molecular mass distributions of PAEs were determined by gel permeation chromatography (GPC). Electrochemical (E′g) and optical band gap (Eoptg ) values of the prepared SBs and PAEs were calculated from cyclic voltammetry (CV) and UV-Vis analyses. The electrochemical band gap (E′g) values of P-1, P-2, P-3 and P-4 were found as 2.44 eV, 2.41 eV, 2.39 eV and 2.39 eV, respectively, from the cyclic voltammetry.

Keywords

  • poly(azomethine-ester)
  • Schiff base
  • water-soluble
  • electrochemical properties
  • thermal degradation
  • elimination reactions
access type Open Access

Studies on structure, growth and characterization of third order nonlinear optical 2-amino-5-chloropyridinium-4-amino benzoate single crystal

Published Online: 26 Jul 2017
Page range: 313 - 321

Abstract

Abstract

Optically transparent single crystals of 2-amino-5-chloropyridinium-4-amino benzoate (2A5CP4AB) were grown at room temperature using solution growth technique. The structure was solved with a support of single crystal XRD, which revealed that the title compound belongs to the monoclinic crystal system having centrosymmetric space group P21/n. The UV-Vis spectrum and photoluminescence properties of the title compound showed the optical transmittance and emission behavior of the compound. The optical band gap was evaluated using the Tauc plot and it was found to be about 3.53 eV. The third order nonlinear optical behavior of the crystal was determined using Z-scan technique. Mechanical properties of the title compound were studied using Vickers microhardness study.

Keywords

  • solution growth
  • nonlinear optical properties
  • photoluminescence
access type Open Access

PbS nanopowder – synthesis, characterization and antimicrobial activity

Published Online: 26 Jul 2017
Page range: 322 - 328

Abstract

Abstract

Lead sulphide (PbS) nanopowder was synthesized by a simple soft chemical route using lead nitrate and thiourea as precursor salts. The as-synthesized nanopowder was characterized by XRD, SEM, EDX, FT-IR, PL, Raman and magnetic measurements. XRD studies reveal the polycrystalline nature of the powder. The powder exhibits face-centered cubic structure with a strong (2 0 0) preferential orientation. The presence of Pb and S in the powder is confirmed by energy dispersive X-ray analysis. The peaks observed at 1112 cm-1 and at 606 cm-1 in the FT-IR spectrum are related to heteropolar diatomic molecules of PbS. The Raman peak shift at 173 cm-1 might have originated from the combination of longitudinal and transverse acoustic phonon modes associated with PbS crystal. The M-H loop confirms the paramagnetic nature of the as-synthesized PbS nanopowder. The nanopowder has significant antimicrobial activity against certain bacteria and fungi strains which make it suitable as antimicrobial agent against pathogenic microorganisms.

Keywords

  • X-ray diffraction
  • photoluminescence
  • energy dispersive X-ray analysis
  • antimicrobial properties
access type Open Access

Effect of deposition temperature on structural, optical and electrical properties of copper bismuth sulphide (CuBiS2) thin films deposited by chemical bath deposition

Published Online: 26 Jul 2017
Page range: 329 - 334

Abstract

Abstract

The effect of deposition temperature on the structural, optical and electrical properties of copper bismuth sulphide (CuBiS2) thin films deposited by chemical bath deposition onto glass substrates at different deposition temperatures (40 °C, 50 °C, 60 °C and 70 °C) for 5 hours deposition time period was investigated. The obtained films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and optical absorption spectra. All deposited films were polycrystalline and had an orthorhombic structure. Their grain size had changed with deposition temperature and their compositions were nearly stoichiometric. The optical band gap value was decreased from 2.44 eV to 2.33 eV with increasing the film thickness. Electrical parameters such as mobility and type of electrical conduction were determined from the Hall effect measurements. They showed that the obtained films have n-type conductivity and mobility values of the copper bismuth sulphide (CuBiS2) films have changed with deposition temperature.

Keywords

  • copper bismuth sulphide (CuBiS2)
  • polycrystalline structure
  • X-ray technique
  • optical band gap
  • Hall coefficient
access type Open Access

Influence of annealing temperature on the structural and optical properties of As30Te70 thin films

Published Online: 26 Jul 2017
Page range: 335 - 345

Abstract

Abstract

Chalcogenide glasses have attracted much attention largely due to their interesting physical and chemical properties. Though few published articles exist on the As-Te system, little is known about the optical properties of eutectic or near eutectic composition of As-Te system upon heat treatment. Therefore, this paper reports the effects of annealing temperature on the structural and optical parameters of As30Te70 thin films. The bulk and thin films of 150 nm thick As30Te70 chalcogenide glasses were prepared by melt-quenching and thermal evaporation techniques, respectively. The glass transition and crystallization reactions of the bulk samples were investigated using differential scanning calorimetry (DSC). The influence of annealing temperature on the transformation of the crystal structure was studied by X-ray diffraction (XRD), while the surface morphology of the annealed samples was examined using scanning electron microscope (SEM). The optical band gap, refractive index and extinction coefficient were also calculated. The DSC scans showed that the melting temperature remains constant at 636.56 K. In addition, other characteristic temperatures such as the glass transition temperature, the onset crystallization temperature, and the crystallization peak temperature increase with increasing the heating rate. The crystalline phases for the as-prepared and annealed films consist of orthorhombic As, hexagonal Te, and monoclinic As2Te3 phases. Furthermore, the average crystallite size, strain, and dislocation density depend on the annealing temperature. The optical absorption results revealed that the investigated films have a direct transition, and their optical energy gap decreases from 1.82 eV to 1.49 eV as the annealing temperature increases up to 433 K. However, the refractive index, extinction coefficient, dielectric constant and the ratio of free carrier concentration to its effective mass, increase with increasing the annealing temperature.

Keywords

  • chalcogenide glasses
  • As-Te system
  • thin films
  • structural
  • optical parameters
  • thermal evaporation
access type Open Access

Excitability of high-energy ultraviolet radiation for Dy3+ in antimony phosphate glasses

Published Online: 26 Jul 2017
Page range: 346 - 354

Abstract

Abstract

Dy3+ doped antimony phosphate (ZASP) glasses are synthesized and the specificity of the luminescence behavior is demonstrated. Different from the conventional long-wave ultraviolet (UVA) exciting cases, the excitable area of Dy3+ doped ZASP glasses is extended to high-energy ultraviolet radiation including medium-wave ultraviolet (UVB) and short-wave ultraviolet (UVC) spectral regions. The quantum efficiency for 4F9/2 level of Dy3+ in low- and medium-concentration Dy2O3 doping cases reaches 95.0 % and 66.7 %, respectively, confirming the emission effectiveness from Dy3+ in ZASP glasses. The values of energy-transfer probability (P) have obvious difference while using 340 nm and 540 nm as monitoring wavelengths, so asthe energy-transfer efficiencies (η), which are related to the energy-transfer processes from discrepant Sb3+ donors to Dy3+ acceptors, were in-equivalent. The effective excitability of high-energy ultraviolet radiation illustrates that Dy3+ doped ZASP glasses are a promising candidate in developing visible light sources, display devices and tunable visible lasers.

Keywords

  • Dy3+
  • antimony phosphate glasses
  • excitability of high-energy ultraviolet radiation
  • energy transfer
access type Open Access

Optical and structural properties of nanostructured copper oxide thin films as solar selective coating prepared by spray pyrolysis method

Published Online: 26 Jul 2017
Page range: 355 - 361

Abstract

Abstract

Copper (II) oxide thin films were prepared by spray pyrolysis method on soda-lime glass substrates using copper acetate precursor solution. Influence of substrate temperature on structural and optical properties was investigated. Structural analysis of these layers were carried out by X-ray diffraction (XRD). Single phase nature and high crystallinity of CuO nanostructures were observed on XRD patterns. The general appearance of the films was uniform and black in color. FT-IR transmittance spectra confirmed the results from the XRD study. Selective solar absorber coatings of copper oxide (CuO) on stainless steel substrates was prepared by spray pyrolysis method. Effect of deposition temperature on optical properties of thin films was investigated. Optical parameters, absorbance (α) and emittance (α) were evaluated from reflectance data. It can be deduced that the porous structure, such as a light traps, can greatly enhance absorbance, while the composition, thickness and roughness of thin films can greatly influence the emissivity. Single phase nature and high crystallinity of CuO nanostructures were observed by XRD patterns. Solar absorbance of thin films were in the range of 85 % to 92 %.

Keywords

  • spray pyrolysis
  • solar selective absorber
  • optical parameters
access type Open Access

Phase evolution and microwave dielectric properties of A5M5O17-type ceramics

Published Online: 26 Jul 2017
Page range: 362 - 367

Abstract

Abstract

A number of A5M5O17 (A = Na, Ca, Sr, La, Nd, Sm, Gd, Dy, Yb; B = Ti, Nb, Ta) type compounds were prepared by a solid-state sintering route and characterized in terms of structure, microstructure and microwave dielectric properties. The compatibility of rare earths with mixed niobate/tantalate and titanate phases was investigated. The larger ionic radii mismatch resulted in the formation of pyrochlore and/or mixed phases while in other cases, pure A5M5O17 phase was formed. The samples exhibited relative permittivity in the range of 35 to 82, quality factor (Q × fo) = 897 GHz to 11946 GHz and temperature coefficient of resonance frequency (τf) = -120 ppm/°C to 318 ppm/°C.

Keywords

  • A5M5O17
  • dielectrics
  • microwave properties
access type Open Access

Kinetic properties and structural analysis of LaCrO3 nanoparticles

Published Online: 26 Jul 2017
Page range: 368 - 373

Abstract

Abstract

LaCrO3 perovskite nanopowders were successfully prepared via a sol-gel method using stoichiometric proportion of materials containing lanthanum and chromium in stearic acid complexing agent. Structural analysis of LaCrO3 indicated an octahedral framework in its XRD pattern bearing crystallite size in the range of 28 nm. The particle sizes were confirmed by morphological scanning of the sample. The optical properties of LaCrO3 nanopowders clearly indicated an interesting optical activity of LaCrO3 in the UV and visible ranges. The degradation activation energy (Ed) was calculated from the output of a moderate thermal programming profile at about 207.97 kJ·mol-1 using Kissinger equation. Capacity, impedance and AC resistance of the perovskites was obtained at 2.970 nF, 2.522 MΩ and 16.19 MΩ, respectively.

Keywords

  • LaCrO3
  • nanoperovskite
  • sol-gel
  • kinetic parameter
access type Open Access

Al-doped ZnO films deposited by magnetron sputtering: effect of sputtering parameters on the electrical and optical properties

Published Online: 26 Jul 2017
Page range: 374 - 381

Abstract

Abstract

Aluminum-doped zinc oxide (AZO) thin films were prepared by magnetron sputtering method. The influences of deposition pressure, substrate temperature, Ar flow rate and film thickness on optical and electrical properties were investigated using ultraviolet-visible (UV-Vis) spectrometer and Hall measurements. The experimental results revealed that a low resistivity, smaller than 4 × 10-4 Ω·cm, was obtained when the deposition pressure was smaller than 0.67 Pa and substrate temperature about 200 °C. Ar flow rate had a small influence on the resistivity but a big influence on the transparency at near infrared range (NIR). We obtained optimized AZO thin films with high ponductivity and transparency at low deposition pressure, small Ar flow and appropriate temperature (around 200 °C). The etching behavior of the AZO thin films deposited at the different Ar flow rates was also studied in this paper. The results show that Ar flow rate is a very important factor affecting the etching behavior.

Keywords

  • AZO thin films
  • optical and electrical properties
  • morphology
access type Open Access

Enhanced thermal conductivity of graphene nanoplatelets epoxy composites

Published Online: 26 Jul 2017
Page range: 382 - 389

Abstract

Abstract

Efficient heat dissipation from modern electronic devices is a key issue for their proper performance. An important role in the assembly of electronic devices is played by polymers, due to their simple application and easiness of processing. The thermal conductivity of pure polymers is relatively low and addition of thermally conductive particles into polymer matrix is the method to enhance the overall thermal conductivity of the composite. The aim of the presented work is to examine a possibility of increasing the thermal conductivity of the filled epoxy resin systems, applicable for electrical insulation, by the use of composites filled with graphene nanoplatelets. It is remarkable that the addition of only 4 wt.% of graphene could lead to 132 % increase in thermal conductivity. In this study, several new aspects of graphene composites such as sedimentation effects or temperature dependence of thermal conductivity have been presented. The thermal conductivity results were also compared with the newest model. The obtained results show potential for application of the graphene nanocomposites for electrical insulation with enhanced thermal conductivity. This paper also presents and discusses the unique temperature dependencies of thermal conductivity in a wide temperature range, significant for full understanding thermal transport mechanisms.

Keywords

  • graphene nanoplatelets
  • thermal conductivity
  • electrical resistivity
  • epoxy resin
  • high-shear exfoliation
access type Open Access

Structural and luminescent properties of Fe3+ doped PVA capped CdTe nanoparticles

Published Online: 26 Jul 2017
Page range: 390 - 397

Abstract

Abstract

During recent decades, magnetic and semiconductor nanoparticles have attracted significant attention of scientists in various fields of engineering, physics, chemistry, biology and medicine. Fe3+ doped PVA capped CdTe nanoparticles were prepared by co-precipitation method and characterized by powder X-ray diffraction, SEM, TEM, FT-IR, optical, EPR and PL techniques to collect the information about the crystal structure, coordination/local site symmetry of doped Fe3+ ions in the host lattice and the luminescent properties of prepared sample. Powder XRD data revealed that the crystal structure belongs to a cubic system and its lattice cell parameters were evaluated. The average crystallite size was estimated to be 8 nm. The morphology of prepared samples was analyzed by using SEM and TEM investigations. Functional groups of the prepared sample were observed in FT-IR spectra. Optical absorption and EPR studies have shown that on doping, Fe3+ ions enter the host lattice in octahedral site symmetry. PL studies of Fe3+ doped PVA capped CdTe nanoparticles revealed UV and blue emission bands. CIE chromaticity coordinates were also calculated from the emission spectrum of Fe3+ doped PVA capped CdTe nanoparticles.

Keywords

  • CdTe
  • PVA
  • co-precipitation
  • iron ions
  • optical absorption
  • EPR
  • FT-IR
  • photoluminescence
access type Open Access

Modelling the power losses in the ferromagnetic materials

Published Online: 26 Jul 2017
Page range: 398 - 404

Abstract

Abstract

In this paper, the problem of describing power losses in ferromagnetic materials is considered. The limitations of Steinmetz formula are shown and a new analytical description of losses in a considered material is proposed. The correctness of the developed description is demonstrated experimentally by comparing the results of calculation with the catalogue characteristics for different ferromagnetic materials.

Keywords

  • ferromagnetic material
  • power loss
  • modelling
  • powder cores
  • ferrite cores
  • nanocrystalline cores
access type Open Access

Preparation and characterization of (Co0:3Zn0:7)(Ti1–xSnx)Nb2O8 microwave dielectric ceramics

Published Online: 26 Jul 2017
Page range: 405 - 411

Abstract

Abstract

Zn0.7Co0.3(Ti1-xSnx)Nb2O8 (x = 0.1, 0.15, 0.2, 0.25, 0.3, 0.35) microwave ceramics were prepared by traditional solidstate reaction method. The influences of Sn substituted for Ti on the phase constitution, crystal structure and microwave dielectric properties of Zn0.7Co0.3(Ti1-xSnx)Nb2O8 ceramics were discussed. The XRD patterns revealed the main phase of ZnTiNb2O8 and little content of Zn0.17Ti0.5Nb0.33O2 secondary phase. With further substitution of Sn, the lattice constant, volume and apparent density of the ceramics increased, the ceramic structure reached a maximal compactness at x = 0.2 which was shown on SEM. Tremendous improvement of Q × f and a declining trend of Ɛr and τf were obtained with increasing x value. Appropriate substitution value (x = 0.10) would ensure excellent microwave dielectric properties (Ɛr = 34.1, Q × f = 40562 GHz, τf =-5 ppm/°C) of the ceramics sintered at 1080 °C.

Keywords

  • microwave dielectric ceramics
  • (Co0.3Zn0.7)(Ti1-xSnx)Nb2O8
  • ixiolite structure
access type Open Access

Ga2O3 nanowires preparation at atmospheric pressure

Published Online: 26 Jul 2017
Page range: 412 - 420

Abstract

Abstract

An attempt has been undertaken to produce gallium oxide nanowires by thermal synthesis from metallic gallium source at atmospheric pressure. Silicon substrates of (1 0 0) and (1 1 1) orientation with and without silicon oxide layers (0.5 μm) were used as support. Evaporated thin gold films were deposited on the top of those silicon carriers as a catalytic agent. After thermal treatment by Rapid Thermal Processing RTP (at various temperatures and times), which was applied to make small Au islands with the diameters of about several tens of nanometers, the substrate surfaces were observed by SEM. The Ga2O3 syntheses were made at various conditions: time, temperature and gas mixture were changed. As a result, monoclinic gallium oxide β-Ga2O3 nanostructures with dominant [1 1 1] and [0 0 2] growth directions were grown. The obtained nanostructures of several tens micrometers length were studied by SEM, PL and X-ray methods.

Keywords

  • Ga2O3
  • nanowires
  • nanobelts
  • thermal synthesis
  • atmospheric pressure
access type Open Access

An impact of the copper additive on photocatalytic and bactericidal properties of TiO2 thin films

Published Online: 26 Jul 2017
Page range: 421 - 426

Abstract

Abstract

The biological and photocatalytic activity of TiO2 and TiO2:Cu in relation to their structure, surface topography, wettability and optical properties of the thin films was investigated. Thin-film coatings were prepared by magnetron sputtering method in oxygen plasma with use of metallic targets (Ti and Ti-Cu). The results of structural studies revealed that addition of Cu into titania matrix (during the deposition process) resulted in obtaining of an amorphous film, while in case of undoped TiO2, presence of nanocrystalline anatase (with crystallites size of 20 nm) was found. Moreover, an addition of cooper had also an effect on surface diversification and decrease of its hydrophilicity. The roughness of TiO2:Cu film was 25 % lower (0.6 nm) as-compared to titania (0.8 nm). These modifications of TiO2:Cu had an impact on the decrease of its photocatalytic activity, probably as a result of the active surface area decrease. Antibacterial and antifungal properties of the thin films against bacteria (Enterococcus hirae, Staphylococcus aureus, Bacillus subtilis, Escherichia coli) and yeast (Candida albicans) were also examined. For the purpose of this work the method dedicated for the evaluation of antimicrobial properties of thin films was developed. It was revealed that Cu-additive has a positive impact on neutralization of microorganisms.

Keywords

  • TiO2
  • thin film
  • microstructure
  • photocatalysis
  • bioactivity
  • optical properties
access type Open Access

Synthesis of Cu and Ce co-doped ZnO nanoparticles: crystallographic, optical, molecular, morphological and magnetic studies

Published Online: 26 Jul 2017
Page range: 427 - 434

Abstract

Abstract

In the present research work, crystallographic, optical, molecular, morphological and magnetic properties of Zn1-xCuxO (ZnCu) and Zn1-x-yCeyCuxO (ZnCeCu) nanoparticles have been investigated. Polyvinyl alcohol (PVA) coated ZnCu and ZnCeCu nanoparticles have been synthesized by chemical sol-gel method and thoroughly studied using various characterization techniques. X-ray diffraction pattern indicates the wurtzite structure of the synthesized ZnCu and ZnCeCu particles. Transmission electron microscopy analysis shows that the synthesized ZnCu and ZnCeCu particles are of spherical shape, having average sizes of 27 nm and 23 nm, respectively. The incorporation of Cu and Ce in the ZnO lattice has been confirmed through Fourier transform infrared spectroscopy. Room temperature photoluminescence spectra of the ZnO doped with Cu and co-doped Ce display two emission bands, predominant ultra-violet near-band edge emission at 409.9 nm (3 eV) and a weak green-yellow emission at 432.65 nm (2.27 eV). Room temperature magnetic study confirms the diamagnetic behavior of ZnCu and ferromagnetic behavior of ZnCeCu.

Keywords

  • copper and cerium co-doped ZnO
  • wurtzite structure
  • transmission electron microscope
  • magnetization
  • optical properties
access type Open Access

Influence of Bi3+ content on photoluminescence of InNbO4:Eu3+,Bi3+ for white light-emitting diodes

Published Online: 26 Jul 2017
Page range: 435 - 439

Abstract

Abstract

A series of red-emitting phosphors InNbO4:Eu3+,Bi3+ was prepared by a high temperature solid-state reaction. The structure, size distribution and luminescence properties of the phosphors were respectively characterized by X-ray diffraction (XRD), laser particle size and molecular fluorescence spectrometer. The XRD results indicate that the phase-pure samples have been obtained and the crystal structure of the host has not changed under the Eu3+ and Bi3+ co-doping. The test of size distribution shows that the phosphor has a normal size distribution. The excitation spectra illustrate that the dominant sharp peaks are located at 394 nm (7F05L6) and 466 nm (7F05D2). Meanwhile, the emission spectra reveal that the phosphors excited by the wavelength of 394 nm or 466 nm have an intense red-emission line at 612 nm owing to the 5D07F2 transition of Eu3+. Bi3+ doping has not changed the peak positions except the photoluminescence intensity. The emission intensity is related to Bi3+ concentration, and it is up to the maximum when the Bi3+-doping concentration is 4 mol%. Due to good photoluminescence properties of the phosphor, the InNbO4:0.04Eu3+,0.04Bi3+ may be used as a red component for white light-emitting diodes.

Keywords

  • red-emitting phosphor
  • photoluminescence properties
  • white LEDs
  • InNbO4
  • solid-state reaction
access type Open Access

Electrical transport and magnetoresistance of double layered CMR manganites R1.2Sr1.8Mn2O7(R = La, Pr, Sm)

Published Online: 26 Jul 2017
Page range: 440 - 446

Abstract

Abstract

Polycrystalline bulk samples of double layered (DL) colossal magnetoresistive (CMR) manganites R1.2Sr1.8Mn2O7 (R = La, Pr, Sm) were prepared by sol-gel method to study the effect of size of lanthanide ion on their magnetotransport properties. The electrical resistivity of the samples was investigated in the temperature range of 70 K to 300 K at different magnetic fields. The samples LSMO and PSMO show insulator-to-metal transition (IMT) behavior, while SSMO sample exhibits insulating behavior in the entire temperature range with a very large value of resistivity. The insulator-to-metal transition temperature (TIM) decreases from 123 K (LSMO) to 90 K (PSMO) and disappears in SSMO sample. To explain the electrical transport above TIM, the temperature dependent resistivity data (T > TIM) of all the samples were fitted to the equations of different conduction models. The results indicate that the conduction at T > TIM is due to Mott variable range hopping (VRH) mechanism in the LSMO and PSMO samples, while Efros-Shkloskii (ES) type of VRH model dominates the conduction process in the SSMO sample. All the three samples show increasing magnetoresistance (MR) even below TIM and the maximum MR is shown by LSMO (39 % at 75 K, 3 T).

Keywords

  • double layered manganites
  • electrical transport
  • magnetoresistance
  • variable range hopping
  • sol-gel process

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