Showing papers in "Materials Science-poland in 2016"

Effect of NaOH concentration on optical properties of zinc oxide nanoparticles

Abstract: Opracowanie ze środkow MNiSW w ramach umowy 812/P-DUN/2016 na dzialalnośc upowszechniającą nauke (zadania 2017).

Chemically synthesized PbS Nano particulate thin films for a rapid NO2 gas sensor

Abstract: Abstract Rapid NO2 gas sensor has been developed based on PbS nanoparticulate thin films synthesized by Successive Ionic Layer Adsorption and Reaction (SILAR) method at different precursor concentrations. The structural and morphological properties were investigated by means of X-ray diffraction and field emission scanning electron microscope. NO2 gas sensing properties of PbS thin films deposited at different concentrations were tested. PbS film with 0.25 M precursor concentration showed the highest sensitivity. In order to optimize the operating temperature, the sensitivity of the sensor to 50 ppm NO2 gas was measured at different operating temperatures, from 50 to 200 °C. The gas sensitivity increased with an increase in operating temperature and achieved the maximum value at 150 °C, followed by a decrease in sensitivity with further increase of the operating temperature. The sensitivity was about 35 % for 50 ppm NO2 at 150 °C with rapid response time of 6 s. T90 and T10 recovery time was 97 s at this gas concentration.

Synthesis and characterization of nanocrystalline barium strontium titanate powder by a modified sol-gel processing

Abstract: Abstract In this research work, nanocrystalline BST (Ba0.6Sr0.4TiO3) powders were synthesized through a modified sol-gel process, using barium acetate, strontium acetate and titanium isopropoxide as the precursors. In this process, stoichiometric proportions of barium acetate and strontium acetate were dissolved in acetic acid and titanium (IV) isopropoxide was added to form BST gel. The as-formed gel was dried at 200 °C and then calcined in the temperature range of 600 to 850 °C for crystallization. The samples were characterized by infrared spectroscopy method (FT-IR), X-ray diffraction technique (XRD) and field emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy. EDS analysis of these samples confirmed the formation of the final phase with the special stoichiometry. The formation of a cubic perovskite crystalline phase with nanoscale dimension was detected using the mentioned techniques. The results showed that the obtained crystallite sizes were 33 and 37 nm for BST powder calcined at 750 and 850 °C, respectively.

VO2(B) conversion to VO2(A) and VO2(M) and their oxidation resistance and optical switching properties

Abstract: Abstract Vanadium dioxide VO2 has been paid in recent years increasing attention because of its various applications, however, its oxidation resistance properties in air atmosphere have rarely been reported. Herein, VO2(B) nanobelts were transformed into VO2(A) and VO2(M) nanobelts by hydrothermal route and calcination treatment, respectively. Then, we comparatively studied the oxidation resistance properties of VO2(B), VO2(A) and VO2(M) nanobelts in air atmosphere by thermo-gravimetric analysis and differential thermal analysis (TGA/DTA). It was found that the nanobelts had good thermal stability and oxidation resistance below 341 °C, 408 °C and 465 °C in air, respectively, indicating that they were stable in air at room temperature. The fierce oxidation of the nanobelts occurred at 426, 507 and 645 °C, respectively. The results showed that the VO2(M) nanobelts had the best thermal stability and oxidation resistance among the others. Furthermore, the phase transition temperatures and optical switching properties of VO2(A) and VO2(M) were studied by differential scanning calorimetry (DSC) and variable temperature infrared spectra. It was found that the VO2(A) and VO2(M) nanobelts had outstanding thermochromic character and optical switching properties.

Core-shell SiO2/Ag composite spheres: synthesis, characterization and photocatalytic properties

Abstract: Abstract Core-shell SiO2/Ag composite spheres with dense, complete and nanoscaled silver shell were prepared by using a novel facile chemical reduction method without surface modification of silica at room temperature. The core-shell composites were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy and energy dispersive X-ray spectroscopy (EDX). The photocatalytic properties towards the degradation of methyl orange (Mo) of the prepared SiO2/Ag composites were also tested. The studies showed that the surface of SiO2 microspheres was homogeneously and completely covered by Ag nanoparticles and the composite exhibited excellent photocatalytic activities. The possible reaction mechanisms for the formation of the silica-silver core-shell spheres were also discussed in this paper.

Structural stability, electronic structure and magnetic properties of the new hypothetical half-metallic ferromagnetic full-Heusler alloy CoNiMnSi

Abstract: Abstract We investigated the structural stability as well as the mechanical, electronic and magnetic properties of the Full-Heusler alloy CoNiMnSi using the full-potential linearized augmented plane wave (FP-LAPW) method. Two generalized gradient approximations (GGA and GGA + U) were used to treat the exchange-correlation energy functional. The ground state properties of CoNiMnSi including the lattice parameter and bulk modulus were calculated. The elastic constants (Cij) and their related elastic moduli as well as the thermodynamic properties for CoNiMnSi have been calculated for the first time. The existence of half-metallic ferromagnetism (HM-FM) in this material is apparent from its band structure. Our results classify CoNiMnSi as a new HM-FM material with high spin polarization suitable for spintronic applications.

Stable phase CdS nanoparticles for optoelectronics: a study on surface morphology, structural and optical characterization

Abstract: Abstract This work presents a study on the surface morphology, structure and optical behavior of stable phase cadmium sulphide (CdS) nanoparticles synthesized via co-precipitation technique. Scanning electron microscopy (SEM) analysis has been employed to study a cluster formation in the aggregated nanoparticles. An image analysis approach using ImageJ has been used to measure the size of nanoparticles from the SEM micrographs. Fourier transform infrared spectroscopic (FT-IR) analysis identified absorption peaks of Cd–S stretching along with moisture content. X-ray diffraction (XRD) analysis showed that CdS nanoparticles crystallized in wurtzite structure with a preferential orientation along (0 0 2) plane. The particle size, microstrain and lattice constants have been evaluated using XRD data. The lattice parameters of these nanoparticles were found to be shorter than the bulk value which led to lattice contraction. The optical absorption study showed a blue shift in the fundamental absorption edge indicating a quantum size effect.

Synthesis and characterization of polyimide thin films obtained by thermal evaporation and solid state reaction

Abstract: In this research we describe the preparation of polyimide with pyromellitic dianhydride (PMDA) and p-phenylene diamine (PDA) thin films by physical vapor deposition. For this study , FTIR Spectrometer has been used to measure the effect of imidization temperature on the chemical structure of vapor-deposited thin films of the aromatic PI. When temperature increases, a general increase in all the absorption peaks is observed by FTIR . The surface topology of the PI films was further examined by using AFM atomic force microscopy as a function of the imidization temperature at 150,200,250 C for 1 hour each in an air circulating oven. The thermal stability of polyimide was also improvedby using Thermogravimetric analysis (TGA).

Effect of calcination temperature on the structural, optical and magnetic properties of pure and Fe-doped ZnO nanoparticles

Abstract: Abstract In the present study, pure ZnO and Fe-doped ZnO (Zn0.97Fe0.03O) nanoparticles were synthesized by simple coprecipitation method with zinc acetate, ferric nitrate and sodium hydroxide precursors. Pure ZnO and Fe-doped ZnO were further calcined at 450 °C, 600 °C and 750 °C for 2 h. The structural, morphological and optical properties of the samples were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and UV-Vis absorption spectroscopy. The X-ray diffraction studies revealed that the as-synthesized pure and doped ZnO nanoparticles have hexagonal wurtzite structure. The average crystallite size was calculated using Debye-Scherrer’s formula. The particle size was found to be in nano range and increased with an increase in calcination temperature. SEM micrographs confirmed the formation of spherical nanoparticles. Elemental compositions of various elements in pure and doped ZnO nanoparticles were determined by EDX spectroscopy. UV-Vis absorption spectra showed red shift (decrease in band gap) with increasing calcination temperature. Effect of calcination on the magnetic properties of Fe-doped ZnO sample was also studied using vibrating sample magnetometer (VSM). M-H curves at room temperature revealed that coercivity and remanent polarization increase with an increase in calcination temperature from 450 °C to 750 °C, whereas reverse effect was observed for magnetization saturation.

Synthesis and study of structural properties of Sn doped ZnO nanoparticles

Abstract: Abstract Pure and Sn-doped ZnO nanostructures were synthesized by simple chemical solution method. In this method we used zinc nitrate and NaOH as precursors. Sn doping content in ZnO was taken with the ratio 0, 5, 10, 15 and 20 percent by weight. Physical properties of Sn-doped ZnO powder were studied by XRD analysis which revealed that Sn doping had a significant effect on crystalline quality, grain size, intensity, dislocation density and strain. The calculated average grain size of pure ZnO was 21 nm. The best crystalline structure was found for 0 wt.%, 5 wt.% and 10 wt.% Sn doping as observed by FESEM and XRD. However, higher Sn-doping (> 10 wt.%) degraded the crystallinity and the grain size of 27.67 nm to 17.76 nm. The structures observed in FESEM images of the samples surfaces were irregular and non-homogeneous. EDX depicted no extra peak of impurity and confirmed good quality of the samples.

Novel GIMS technique for deposition of colored Ti/TiO₂ coatings on industrial scale

Abstract: Abstract The aim of the present paper has been to verify the effectiveness and usefulness of a novel deposition process named GIMS (Gas Injection Magnetron Sputtering) used for the flrst time for deposition of Ti/TiO₂ coatings on large area glass Substrates covered in the condition of industrial scale production. The Ti/TiO₂ coatings were deposited in an industrial System utilizing a set of linear magnetrons with the length of 2400 mm each for covering the 2000 × 3000 mm glasses. Taking into account the speciflc course of the GIMS (multipoint gas injection along the magnetron length) and the scale of the industrial facility, the optical coating uniformity was the most important goal to check. The experiments on Ti/TiO₂ coatings deposited by the use of GIMS were conducted on Substrates in the form of glass plates located at the key points along the magnetrons and intentionally non-heated during any stage of the process. Measurements of the coatings properties showed that the thickness and optical uniformity of the 150 nm thick coatings deposited by GIMS in the industrial facility (the thickness differences on the large plates with 2000 mm width did not exceed 20 nm) is fully acceptable form the point of view of expected applications e.g. for architectural glazing.

Effect of cerium on structural and optical properties of ZnO aerogel synthesized in supercritical methanol

Abstract: Abstract Pure ZnO and Ce-doped (5 at.%) ZnO aerogels were prepared by dissociation of dihydrate zinc acetate and cerium nitrate in methanol, followed by drying in supercritical conditions of the solvent. The concentration of zinc acetate solution and the atomic ratio Ce/Zn were fixed at 0.2 mol/L and 0.05 mol/L, respectively. XRD results showed a hexagonal wurtzite structure of ZnO aerogel crystallites and a formation of a separate second phase of ceria cubic phase with fluorite structure and 7.4 nm in size. The introduction of cerium in the solution had a negative effect on the aerogel crystalline quality. The crystallites size was found to be 16 nm in pure ZnO and 27 nm in Ce-doped ZnO aerogels. The grains of Ce-doped ZnO aerogel had torus shaped morphology with hollow centers, but those of pure ZnO were flattened semispheres. The calculated values of different structural parameters showed that cerium ions introduced into the ZnO lattice occupied interstitial sites and Zn ions substituted Ce ones in ceria lattice during the formation process. FT-IR and UV-Vis absorption spectra have not revealed any particularities due to the presence of cerium atoms in ZnO, indicating that Ce (5 at.%) doping of ZnO crystallites synthesized in supercritical methanol did not strongly affect the optical gap of the semiconductor. Micro-Raman studies confirmed the formation of cubic fluorite structure ceria in ZnO aerogel and showed that Raman active modes of ZnO are amplified with the presence of ceria.

Dielectric, etching and Z-scan studies of glycine doped potassium thiourea chloride crystal

Abstract: Abstract Glycine doped potassium thiourea chloride (PTC) crystal has been grown by slow solution evaporation technique. The dielectric studies have been employed to examine substantial improvement in dielectric constant and dielectric loss of glycine doped PTC crystal. The etching studies have been performed to investigate the surface quality of this crystal. The z-scan studies have been carried out at 632.8 nm to explore the third order nonlinear optical nature. The negative nonlinear refraction of glycine doped PTC crystal was found to be of 7.27 × 10−12 cm2/W. The origin of high magnitude of third order nonlinear optical susceptibility and reverse saturable nonlinear absorption have been investigated. The obtained results were explored to discuss the nonlinear optical applications of PTC crystal.

Colossal dielectric constant of NaNbO3 doped BaTiO3 ceramics

Abstract: Abstract BaTiO3 ceramics doped with 0.40 mol% NaNbO3 were prepared using a traditional approach by sintering at temperature of 1250 °C to 1290 °C. The prepared ceramics was characterized by very good dielectric properties, such as high dielectric constant (1.5 × 105), low dielectric loss (0.1), and good dielectric temperature stability in the −40 °C to 100 °C range for the sample sintered below 1270 °C. The dielectric characteristics obtained with XPS confirmed that Ti4+ ions remain in the state without any change. The huge increase in dielectric constant in NaNbO3 doped BaTiO3 samples occurs when large amount of Ba2+ ions are excited to a high energy bound state of Ba2+ − e or Ba+ to create electron hopping conduction. For samples with the content of NaNbO3 higher than 0.40 mol%, or sintering temperature higher than 1280 °C, compensation effect is dominated by cation vacancies with sharply decreasing dielectric constant and increased dielectric loss. The polaron effect is used to explain the relevant mechanism of giant dielectric constant appearing in the ferroelectric phase.

Site preference and electronic structure of Mn2RhZ (Z = Al, Ga, In, Si, Ge, Sn, Sb): a theoretical study

Abstract: Abstract The electronic structure and magnetism of Mn2RhZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) Heusler alloys have been studied by using first-principles calculations. Three half-metallic ferromagnets, namely, Mn2RhAl, Mn2RhGe and Mn2RhSb have been considered. The calculated equilibrium lattice constant increases with increasing atomic number of Z atoms lying in same column of periodic table. The calculated total magnetic moments Mtot are 2 µB/f.u. for Mn2RhAl and Mn2RhGa, 3 µB/f.u. for Mn2RhSi, Mn2RhGe and Mn2RhSn, and 4 µB/f.u. for Mn2RhSb, which agrees with the Slater-Pauling curve quite well. In all these compounds, except for Mn2RhSb, the moments of Mn (A) and Mn (B) are antiparallel to each other. The total magnetic moments of the three considered half-metals assume integral values in a wide range of equilibrium lattice parameters.

Investigation on nonlinear optical and dielectric properties of L-arginine doped ZTC crystal to explore photonic device applications

Abstract: Abstract The present study is focused to explore the photonic device applications of L-arginine doped ZTC (LA-ZTC) crystals using nonlinear optical (NLO) and dielectric studies. The LA-ZTC crystals have been grown by slow evaporation solution technique. The chemical composition and surface of LA-ZTC crystal have been analyzed by means of energy dispersive spectroscopy (EDS) and surface scanning electron microscopy (SEM) techniques. The Vicker’s microhardness study has been carried out to determine the hardness, work hardening index, yield strength and elastic stiffness of LA-ZTC crystal. The enhanced SHG efficiency of LA-ZTC crystal has been ascertained using the Kurtz-Perry powder SHG test. The closed-and-open aperture Z-scan technique has been employed to confirm the third order nonlinear optical nature of LA-ZTC crystal. The Z-scan transmittance data has been utilized to calculate the superior cubic susceptibility, nonlinear refractive index, nonlinear absorption coefficient and figure of merit of LA-ZTC crystal. The behavior of dielectric constant and dielectric loss of LA-ZTC crystal at different temperatures has been investigated using the dielectric analysis.

Wrinkled graphene: synthesis and characterization of few layer graphene-like nanocarbons from kerosene

Abstract: Abstract Wrinkled graphene, derived from a facile thermal decomposition and chemical method, was subjected to various analysis techniques and the results have been reported here. Raman studies revealed the presence of highly graphitized amorphous carbon, which was evident by the appearance of five peaks in the deconvoluted first order spectrum. This result was very well corroborated by the XRD analysis. XPS and FT-IR spectra confirmed the incorporation of oxygen functionalities into the carbon backbone. AFM and SEM images of the sample disclosed a cluster of few-layer wrinkled graphene fragments. TEM images displayed a chain of nearly spherical aggregates of graphene, resembling nanohorns. The resistivity and sheet resistance of the sample were found to be low, making the obtained material a promising candidate for various device applications. Hence, kerosene soot proved to be an efficient precursor for facile synthesis of few layer graphene-like nanocarbon.

Optimization of S:Sn precursor molar concentration on the physical properties of spray deposited single phase Sn2S3 thin films

Abstract: Abstract Nanoneedle structured Sn2S3 thin films were prepared by spray pyrolysis technique from aqueous solutions of tin (II) chloride and thiourea, keeping the molar concentrations of S:Sn = 0.01:0.01, 0.02:0.02, 0.03:0.03 and 0.04:0.04 in the starting solutions. XRD studies reveal that all the films exhibit orthorhombic crystal structure with a preferential orientation along the [2 1 1] direction. The peak intensity of the (2 1 1) plane is found to be maximum for the film coated with 0.02:0.02 S:Sn molar concentration which confirms the improved crystalline nature of this film. SEM images depict that the film coated with S:Sn molar concentration 0.02:0.02 exhibit needle shaped grains. The optical band gap exhibits red shift from 2.12 eV to 2.02 eV with an increase in S:Sn precursor molar concentration. Electrical studies show that the films having S:Sn molar concentrations 0.01:0.01 and 0.02:0.02 exhibit minimum resistivity values of 0.238 and 0.359Ω ·cm, respectively. © Wroclaw University of Technology.

Structural and optoelectronic properties of glucose capped Al and Cu doped ZnO nanostructures

Abstract: Abstract Al and Cu doped ZnO nanoparticles are considered as appropriate for modulation of structural and optoelectronic properties. Al atoms are found to substitute the host Zn whereas Cu dopants mainly segregate in grain boundaries and thereby determine the optical properties. The undoped as well as Al and Cu doped ZnO exhibit spherical well defined particles. The spherical nanoparticles change to rod type structures on co-doping. The average particle size decreases on doping what consequently results in an increment in band gap. Blue shift in UV absorption is governed by the functional group of glucose; further blue shift occurring on metal doping may be attributed to Burstein-Moss effect. PL spectra of doped and undoped ZnO show a dominant near band gap UV emission along with visible emission owing to the defects. The PL peak intensity increases on doping with Cu and Al. The linear I-V characteristics indicate the ohmic behavior of ZnO nanostructures.

Structural and electrical properties of chromium substituted nickel ferrite by conventional ceramic method

Abstract: Abstract Polycrystalline Cr substituted Ni ferrites [NiCrxFe2−xO4 (0.0 ≤ x ≤ 1.0)] were synthesized by conventional ceramic method and sintered at 1350 °C in air. X-ray diffraction (XRD) patterns showing sharp peaks confirmed the formation of single phase cubic spinel structure. The lattice parameters of the samples were determined from the XRD data using Nelson-Riley extrapolation technique. They were found to decrease with increasing Cr concentration obeying Vegard’s law. X-ray density, bulk density and porosity were also calculated from the XRD data. The variation of DC resistivity with temperature was measured by two-probe method. The DC resistivity was found to decrease with increasing temperature indicating the semiconducting nature of the samples. Activation energy was calculated from the Arrhenius plot. AC resistivity, dielectric constant and loss tangent were measured in the frequency range of 1 kHz to 120 MHz at room temperature.

The effect of pressure and alloying on half-metallicity of quaternary Heusler compounds CoMnYZ (Z = Al, Ga, and In)

Abstract: Abstract In this work, first-principles calculations of the structural, electronic and magnetic properties of Heusler alloys CoMnYAl, CoMnYGa and CoMnYIn are presented. The full potential linearized augmented plane waves (FP-LAPW) method based on the density functional theory (DFT) has been applied. The structural results showed that CoMnYZ (Z = Al, Ga, In) compounds in the stable structure of type 1+FM were true half-metallic (HM) ferromagnets. The minority (half-metallic) band gaps were found to be 0.51 (0.158), 0.59 (0.294), and 0.54 (0.195) eV for Z = Al, Ga, and In, respectively. The characteristics of energy bands and origin of minority band gaps were also studied. In addition, the effect of volumetric and tetragonal strain on HM character was studied. We also investigated the structural, electronic and magnetic properties of the doped Heusler alloys CoMnYGa1−xAlx, CoMnYAl1−xInx and CoMnYGa1−xInx (x = 0, 0.25, 0.5, 0.75, 1). The composition dependence of the lattice parameters obeys Vegard’s law. All alloy compositions exhibit HM ferromagnetic behavior with a high Curie temperature (TC).

Influence of Ta2O5 doping on mechanical and biological properties of silicate glass-ceramics

Abstract: Abstract The mechanical properties of silicate glass-ceramics were evaluated based on the compressive strength tests. It was found that Ta2O5 addition improved densification, refinement of the microstructure and toughening of the bodies. The maximum compressive strength of the bodies with 1 mol% Ta2O5 was increased 3-fold (245.92 ±0.3 MPa) in comparison to undoped glass-ceramics which was measured to be 89.04 ±0.3 MPa, while for 3 mol% it became 4-fold (387.12 ±0.4 MPa) greater. The addition of Ta2O5 stabilized the system by controlling the biodegradation of the glass-ceramics. It effectively depressed the apatite formation as by addition of 3 mol% Ta2O5 no apatite layer was observed. It may be concluded from this study that mechanical and physical properties can be improved by the addition of Ta2O5, but at a cost of bioactivity. Still the optimized composition having Ta2O5 ⩽ 1 mol% may provide appropriate strength of biomaterials for high load bearing applications.

Quantum chemical studies on the molecular structure, spectroscopic and electronic properties of (6-Methoxy-2-oxo-2H-chromen-4-yl)-methyl pyrrolidine-1-carbodithioate

Abstract: Abstract In this paper, the molecular geometry, vibrational frequencies and chemical shifts of (6-Methoxy-2-oxo-2H-chromen-4-yl)methyl pyrrolidine-1-carbodithioate in the ground state have been calculated using the Hartree-Fock and density functional methods with the 6-311++G(d,p) basis set. To investigate the nonlinear optical properties of the title compound, the polarizability and the first hyperpolarizability were calculated. The conformational properties of the molecule have been determined by analyzing molecular energy properties. Using the time dependent density functional theory, electronic absorption spectra have been calculated. Frontier molecular orbitals, natural bond orbitals, natural atomic charges and thermodynamical parameters were also investigated by using the density functional theory calculations.

Effect of deposition time on surface plasmon resonance and Maxwell-Garnett absorption in RF-magnetron sputtered carbon-nickel films

Abstract: Abstract In this work, carbon-nickel films were grown during four deposition times (50 s, 90 s, 180 s and 600 s) at room temperature on glass substrates by radio frequency magnetron sputtering. The optical absorption spectra of the films were investigated with a special emphasis on the surface plasmon resonance (SPR) of Ni nanoparticles. The optical absorption peaks caused by the surface plasmon resonance of Ni nanoparticles were observed in the wavelength range of 300 nm to 330 nm. It has been shown that the surface plasmon resonance peaks exhibit a red shift and a blue shift depending on the deposition time. The red and blue shifts of the surface plasmon resonance in the absorption spectra of the films were observed with the increase and decrease of Ni nanoparticle size, respectively. The Ni nanoparticle size, dielectric function of carbon matrix εm and plasma frequency of free electrons ωp for the films deposited at deposition time of 180 s have maximum values of 80 nm, 0.401 and 7.25 × 1015 s–1, respectively. These observations are in a good agreement with the electrical resistivity measurements and Maxwell-Garnett (M-G) effective medium theory (EMT).

Investigations of optical and surface properties of Ag single thin film coating as semitransparent heat reflective mirror

Abstract: Abstract The paper presents results of optical and surface morphology investigations of semitransparent silver single thin films deposited on glass substrate in relation to their heat radiation treatment. The thickness of 15 nm for the silver thin films was selected using computer designing of optical spectra and the films were deposited using electron beam evaporation process. Optical transmission and reflection were investigated for as deposited samples and after exposition to heat radiation from quartz-halogen lamp. The changes in the optical spectra were observed which suggested degradation of deposited heat mirrors. Structure and surface morphology studies performed using scanning electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy allowed us to conclude about formation of nanometric silver islands, regularly distributed over the surface of the glass substrate after exposure to heat treatment.

Electronic structure and optical properties of (BeTe)n/(ZnSe)m superlattices

Abstract: Abstract The structural, electronic and optical properties of (BeTe)n/(ZnSe)m superlattices have been computationally evaluated for different configurations with m = n and m≠n using the full-potential linear muffin-tin method. The exchange and correlation potentials are treated by the local density approximation (LDA). The ground state properties of (BeTe)n/(ZnSe)m binary compounds are determined and compared with the available data. It is found that the superlattice band gaps vary depending on the layers used. The optical constants, including the dielectric function ε(ω), the refractive index n(ω) and the refractivity R(ω), are calculated for radiation energies up to 35 eV.

Hydrothermal synthesis and thermoelectric properties of PbS

Abstract: Abstract In this paper, hydrothermal approach combined with high pressure sintering method was employed to synthesize PbS. The X-ray diffraction results show that single phase PbS can be obtained by a simple hydrothermal method. The scanning electron microscope results show that the PbS sample has nearly cubic shape and preserves well crystallized and coarse grains after high pressure sintering. The thermoelectric performance of PbS obtained in this study is comparable to that of a PbS sample prepared by conventional method. The carrier type and concentration of PbS can be tuned effectively by doping with Bi. The maximum figure of merit for PbS doped with 1 mol% Bi reaches 0.44 at 550 K, which is about 30 % higher than that of undoped PbS. These results indicate that hydrothermal method provides a viable and controllable way of tuning the electrical transport and thermoelectric properties for PbS.

Novel and facile synthesis of transparent-monolithic TiO2 gels by sol-gel method based on an esterification reaction

Abstract: Abstract Transparent TiO2 monoliths were obtained through a modified sol-gel route from titanium isopropoxide as a precursor. By controlling the hydrolysis of this precursor through the intermediate of esterification reaction between acetic acid and isopropanol at 40 °C, transparent TiO2 xerogel monoliths were obtained. The monoliths prepared by this method were transparent in the wavelengths between 400 nm and 700 nm. Fourier transform infrared (FT-IR) spectroscopy suggested that the acetic acid played also an active role as a chelating agent, forming Ti[(OH)y(OOCCH3)x] less reactive species. Powder X-ray diffraction confirmed the amorphous-to-anatase phase transformation with the formation of unknown Ti-containing complex at 90 °C. Only anatase TiO2 could be observed in the samples calcined at 250 °C and 450 °C. Optical aspects of the gel (transparent-transluscent transformation of monolithic gel) and gelation time were controlled by changing the amount of external water.

Structural and electrochemical investigation of waste newspaper based electrodes for supercapacitor applications

Abstract: Abstract There is a general consensus to develop renewable energy storage and conversion technologies to replace fossil fuel energy for sustainable development. Currently, the development of high performance energy storage and conversion devices is an important step on the road to alternative energy technologies. With a special focus on the upgradation of waste to valuable energy, this paper presents an effective synthetic method that utilizes waste newspapers as the precursor to prepare the activated carbon electrodes by the pyrolysis and chemical activation processes. The amorphous nature and surface morphology of the carbon samples were confirmed by XRD and SEM analysis, respectively. Activated waste newspaper carbon (AWNP) showed good electrochemical properties at 800 °C and its specific capacitance at a scan rate of 2 mV/s was found to be 380 F/g. It is important to mention that the source of the raw material is cost effective and suitable for green technology.

Synthesis, investigation on structural and electrical properties of cobalt doped Mn–Zn ferrite nanocrystalline powders

Abstract: Abstract Synthesis of CoxMnyZnyFe2O4 (x = 0.1, 0.5, 0.9 and y = 0.45, 0.25, 0.05) nanocrystalline powders was done by chemical co-precipitation method. The crystal structure was determined by using X-ray diffraction (XRD) studies. The crystallite size and lattice parameters were calculated from the XRD data. The XRD results revealed that the crystallite size of the nanocrystalline powder was found to decrease from 37 nm to 28 nm with the substitution of cobalt. The effect of cobalt ions on the crystallization process, the lattice parameters and electrical properties of Mn–Zn ferrites has been also investigated. The AC conductivity increased with an increase in frequency but it decreased with an increase in cobalt content. The complex impedance analysis of the data showed that the resistive and capacitive properties of the Co–Mn–Zn ferrite are predominant due to the fact that the processes are associated with the grains and grain boundaries. The dielectric constant and dielectric loss dependence on doping level and frequency at room temperature were also studied.