• Volume 38, Issue 1

February 2015,   pages  1-282

• Influence of dysprosium addition on the structural, morphological, electrical and magnetic properties of nano-crystalline W-type hexaferrites

Dysporium (Dy)-substituted W-type barium hexaferrites were prepared by the citrate sol–gel-method. Crystalline structure, morphology, magnetic properties, DC resistivity and microwave absorption properties of BaNi2Dy𝑥Fe16−𝑥O27 (𝑥 = 0-0.9) were studied using X-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometer and vector network analyzer and sensitive source meter, respectively. Single-phase W-type barium hexaferrites, with a chemical composition of BaNi2Dy𝑥Fe16−𝑥O27 (𝑥 = 0-0.9), were formed by being heated at 1250°C for 4 h in air. The magnetic properties such as saturation magnetization (𝑀s), and coercivity (𝐻c) were calculated from hysteresis loops. Hysteresis loop measurements show that the coercivity values lie in the range of 530–560 Oe with increasing Dy content. It was also observed that magnetization decreases with the increase of Dy content. The DC resistivity was observed to increase from 0.83 × 107 to 6.92 × 107 𝛺 cm with increasing Dy contents due to the unavailability of Fe3+ ions. Microwave absorption properties of hexaferrite (70 wt%)–acrylic resin (30 wt%) composites were measured by the standing-wave-ratio (SWR) method in the range from 12 to 20 GHz. For sample with 𝑥 = 0.6, a minimum reflection loss of −40 dB was obtained at 16.2 GHz for a layer of 1.7 mm in thickness. Sample with 𝑥 = 0.9 had wide bandwidth absorption in the frequency range of 13.5–18 GHz with reflection losses less than −15 dB. Meanwhile the minimum reflection point shifts toward higher frequency with the increase of Dy content.

• Preliminary comparison of different reduction methods of graphene oxide

The reduction of graphene oxide (GO) is a promising route to bulk produce graphene-based sheets. Different reduction processes result in reduced graphene oxide (RGO) with different properties. In this paper three reduction methods, chemical, thermal and electrochemical reduction, were compared on three aspects including morphology and structure, reduction degree and electrical conductivity by means of scanning electron microscopy (SEM), X-ray diffraction(XRD), the Fourier transform infrared spectroscopy (FT-IR) spectrum, X-ray photoelectron spectroscopy (XPS) and four-point probe conductivity measurement. Understanding the different characteristics of different RGO by preliminary comparison is helpful in tailoring the characteristics of graphene materials for diverse applications and developing a simple, green, and efficient method for the mass production of graphene.

• Synthesis and structural characterization of new inorganic–organic hybrid: arsenomolybdate compound with cytosinium cations

New organic–inorganic hybrid compound, with formula (C4H6N3O)6 [(HAsO4)2Mo6O19].7H2O, was prepared and characterized by IR and UV–visible spectroscopies and X-ray diffraction techniques. Thermal analysis was performed to study their thermal stability. The crystal structure of the title compound (triclinic, space group $P − 1$, 𝑍 = 2) was determined by X-ray diffraction. The compound contains the polyanion [(HAsO4)2Mo6O19]6−, which consists of the six molybdenum octahedral grouped into two parts consisting of four edge-sharing octahedral and two face-sharing octahedral, respectively, these two parts are connected by two corner-sharing O atoms to form a bent Mo6 ring. The polyanion framework derives from the Strandberg type and it is a new isomer. The cytosinium cations (Cyt+) are embedded in the channels and interact with the inorganic framework by way of N-H $\cdots$ O and O-H $\cdots$ O hydrogen bonds. Furthermore, the electrochemical property of this compound has been studied.

• Oxygen separating membrane manufactured from Ba0.5Sr0.5Co0.8Fe0.2O3−𝛿 perovskite-like material

The dense thin membrane for oxygen separation was manufactured from Ba0.5Sr0.5Co0.8Fe0.2O3−𝛿 (BSCF) mixed oxide with perovskite-like structure prepared by the solid-state method. Properties of both powder and granulate (chemical and phase compositions, the specific surface area and the porosity) as well as sintered material (the apparent density, the apparent porosity, the water absorbability, the chemical composition, the crystallo-graphic structure and microstructure), that affect the process of ion oxygen permeation through membrane, were determined. Parameters influencing on usable properties of membranes viz., the bending strength and the coefficient of thermal expansion were assessed as well. Effect of the sintering temperature on membrane structure was evaluated. The elaborated fabrication procedure enables one to manufacture membrane, in which microstructure is characterized by the presence of big grains as well as decreased concentration of grain boundaries. Measurements of the oxygen permeation through BSCF membrane revealed that the highest oxygen flux reaching 2.6 cm3 O2/ (cm2 min) was obtained at 950°C under air and helium flows equal to 1 dm3 min−1.

• Yttrium deposition on mesoporous TiO2: textural design and UV decolourization of organic dyes

This study discusses about the photochemical, topological and textural properties of yttrium-doped titanium dioxide (TiO2) photocatalysts. The mesoporous yttrium-doped TiO2 substrates prepared in this research work operate efficiently via low-cost commercial 13-W UV lamps. A quantity of 2 wt% yttrium deposition on TiO2 accelerates methyl orange UV decolourization kinetics. When Y content increases to 8 wt%, besides anatase, rutile is formed from 600°C. The Y2Ti2O7 photoinactive compound emerges at 800°C. The P-123 surfactant mesopore templating treatment of TiO2 xerogels (when concurrent with the sol–gel Y-doping of Ti alkoxides) features the following two correlated phenomena: (i) The surface area increases while the access to the inner porosity of the substrate becomes much easier, so that a larger portion of the surface is made accessible to the dye molecules as well as to the yttrium dopant; (ii) the inclusion of tubular instead of ink-bottle pores facilitates the transport of organic species in and out of the pore structure. The most active mesoporous substrate resulted to be made of 2 wt% Y; contrastingly, when Y= 8 wt%, photoinactivity arose because of Y2Ti2O7 formation. The involvement of P123 was not the sole factor influencing the efficiency of TiO2 mesoporous photocatalysts. There were additional key factors, such as the surging of co-ordination and nucleophilic species, during the dye photodegradation process, which were also induced by the presence of Y species on the surface of these substrates.

• Space-charge-limited conduction in Se90Sb4Ag6 glassy alloy: observation of Meyer–Neldel rule

The present paper reports the measurements of space-charge-limited conduction (SCLC) in glassy Se90Sb4Ag6 alloy. For this purpose, 𝐼–𝑉 characteristics have been taken at certain fixed temperatures. The results indicate that super-ohmic behaviour is observed at high electric fields. The results fit well with the theory of SCLC for the uniform distribution of traps. From the temperature dependence of conductivity, activation energy is obtained at different electric fields, which is found to be field dependent. Pre-exponential factor is found to depend on the activation energy and obeys Meyer–Neldel rule.

• Growth of 2-amino-5-chlorobenzophenone single crystal by Microtube Czochralski method and its characterization

Organic single crystals of 2-amino-5-chlorobenzophenone (2A5CB) were grown by Microtube Czochralski method using Microtube as a seed. The grown crystals were characterized by single crystal and powder X-ray diffraction. The functional groups of the grown crystal were found using Fourier transform infrared spectroscopy. The cutoff wavelength of 2A5CB has been identified using UV–vis–NIR studies. Thermogravimetric/differential thermal analysis (TG/DTA) has been carried out to find the thermal behaviour. 2A5CB was found to be thermally stable up to 125°C. Powder second harmonic generation (SHG) was investigated to explore its nonlinear optical (NLO) properties. The mechanical stability of 2A5CB is studied by using Vickers hardness testing.

• Effect of the addition of 3-glycidoxypropyltrimethoxysilane to tetraethoxyorthosilicate-based stone protective coating using 𝑛-octylamine as a catalyst

A tetraethoxyorthosilicate (TEOS)-based stone protective coating containing functional 3-glycidoxypropyltrimethoxysilane (GPTMS) has been prepared in order to reduce gel crack formation during the drying phase using 𝑛-octylamine as a catalyst. The effect of gel time and viscosity on GPTMS concentration were studied.We have demonstrated that the addition of GPTMS accelerated the gel process and improve viscosity of sol. It was found that GPTMS was chemically incorporated into the gel matrix via Si–O bonds by Fourier transform infrared spectroscopy (FTIR) analysis. Nitrogen adsorption–desorption isotherms of xerogels were measured, they showed that the pore size of xerogels decreased with the addition of GPTMS. Atomic force microscopy (AFM) showed the surface roughness increased as content of GPTMS was higher. The Scotch Tape test and the hardness values showed improvement of cohesion and consolidation ability of hybrid sol. The protective performance evaluation of the treated stones with hybrid sol indicated its acid rain resistance.

• Synthesis of poly(furfuryl alcohol)/montmorillonite nanocomposites by direct in-situ polymerization

The purpose of this study was to obtain poly(furfuryl alcohol) nanocomposites with Algerian organically modified clay (termed 12-montmorillonite). The formation of poly(furfuryl alcohol) was confirmed by infrared spectroscopy (IR); the prepared nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The evolution of mechanical properties was also studied. The obtained results confirm the intercalation of molecules of salt in the clay layers, and a good interaction with the polymer, showing the formation of intercalated and/or exfoliated structures. The nanocomposites showed higher thermal stability compared to pure polymer, and the mechanical properties presented interesting and promising results.

• Dependence of ZnO-based dye-sensitized solar cell characteristics on the layer deposition method

The selection of a proper method for the semiconductor layer deposition is an important requirement towards a high efficiency for dye-sensitized solar cells (DSSCs). We compared three techniques for deposition of the semiconductor thin layer in ZnO-based DSSCs, in order to determine the dependence between the deposition method, the ZnO film properties and finally the DSSCs characteristics. For this purpose, we varied the method used for deposition of the semiconductor film and we replaced ZnO with Al-doped ZnO. The nanostructured films morphology was analysed by transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction. The optical properties were examined by UV–visible spectroscopy and the bandgap energies were calculated using the Tauc equation. The higher fill factor value was registered for DSSCs based on the ZnO film obtained by electrochemical method, but the higher efficiency was registered for doctorblading method.

• Growth, characterization and dielectric studies of gadolinium fumarate heptahydrate single crystals

Gadolinium fumarate heptahydrate single crystals were grown by the single gel diffusion technique using silica gel as a medium of growth. Nucleation rate of these crystals was studied corresponding to the effect of various growth parameters. An attempt was made to relate the experimental results with the classical nucleation theory. The crystals were characterized by different physico-chemical techniques of characterization. Powder X-ray diffraction pattern showed that gadolinium fumarate is a crystalline compound and is isomorphous with samarium fumarate heptahydrate crystals. Fourier transform infrared spectroscopy was performed for the identification of water and other functional groups present in the compound. Elemental analysis sugested the chemical formula of the crystals to be Gd2(C4H2O4)3.7H2O. The presence of seven molecules of water was also supported by the thermogravimetric analysis. The hydrated compound was found to be thermally stable up to a temperature of about 110°C and its anhydrous form up to the temperature of 420°C. The thermal decomposition of the compound in the nitrogen atmosphere leads to the formation of gadolinium oxide as the final product. The dielectric properties and AC conductivity of gadolinium fumarate heptahydrate complex were carried out in the frequency range of 20 Hz–3MHz and over the temperature range of 15–130°C, both showing a hump at about 95°C, which could be attributed to water molecules in the crystal boundary.

• Preparation and characterization of Bi2S3 compound semiconductor

Bi2S3 single crystals were grown by the chemical vapour transport technique using ammonium chloride (NH4Cl) as a transporting agent. The stoichiometry of Bi2S3 single crystal was confirmed by energy-dispersive analysis of X-rays (EDAX). The powder X-ray diffraction (XRD) pattern showed that Bi2S3 crystals belong to the orthorhombic phase with calculated lattice constant 𝑎 = 11.14 Å, 𝑏 = 11.30 Å and 𝑐 = 3.96 Å. Scanning electron microscopy (SEM) pictures indicate the presence of layer lines on the surface of crystals thereby proving that these crystals are grown by layer by layer mechanism.We studied the transport properties viz. Hall effect, resistivity, thermoelectric power and thermal conductivity on Bi2S3 pellets. Raman spectroscopy and thermal gravimetric analysis (TGA) were carried out on Bi2S3 single crystal for studying their optical and thermal behaviours.

• Effect of Er doping on the superconducting properties of porous MgB2

MgB2 bulk sample with porous structure was produced by using the in-situ solid-state reaction method under argon (Ar) atmosphere of 10 bar. Elemental Er in powder form was doped into MgB2 with different compositions (Mg1−𝑥Er𝑥)B2, where 𝑥 = 0.00, 0.03 and 0.05, in order to investigate the effect of rare-earth (RE) element Er on the structural and electromagnetic properties of porous MgB2. The Er-doped samples result in small grain size structure compared to the undoped one. The lattice constants 𝑎 and 𝑐 of the doped samples, determined from X-ray diffraction (XRD) analysis, increase with the increasing Er content, and consequently the superconducting transition temperature ($T^{\text{onset}}_{c}$) of MgB2, determined from resistivity measurements, is slightly suppressed. Also, the upper critical field ($B_{c2}$), the irreversibility field ($B_{\text{irr}}$) and the critical current density ($J_{c}$) values are significantly enhanced in the doped samples. For the best sample (𝑥 = 0.03), at 15 K under a magnetic field of 4 T, the $J_{c}$ value reaches 2.4×104 A cm-2, which is higher than that of the porous sample by an order of 103, and the $B_{\text{irr}}$ value at 20 K reaches 9.7 T. These results imply that the RE element Er fills the pores, enhances the density and the grain connectivity. Hence, the superconducting properties of the porous MgB2 sample improve by Er doping.

• Synthesis, characterization and magnetic property of 3D flower-like nickel sulphide nanocrystals through decomposing bis(thiourea) nickel(II) chloride crystals

Three-dimensional (3D) flower-like cubic Ni3S4 nanoplates with single crystalline nature were successfully prepared through decomposing bis(thiourea) nickel(II) chloride crystals (BTNC). The samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, selected area electron diffraction and Raman spectroscopy. Results show that the as-prepared products are pure cubic Ni3S4 and stable in range of 180–220°C with single crystal nature providing high surface areas, and higher reaction temperature leads to lower surface areas. Typical Raman peaks of the as-synthesized 3D flower-like cubic Ni3S4 at 200°C are located at 239, 286, 337, 379, 423, 478 and 630 cm-1. Magnetization measurement indicates that single crystalline Ni3S4 nanoplates prepared at 200°C displays antiferromagnetic behaviour.

• Magnetocaloric response of La0.70Ca0.1Sr0.2Fe0.1Mn0.9O3 pervoskite for magnetic refrigeration

The complex magnetic materials La0.70Ca0.1Sr0.2Fe0.1Mn0.9O3 (LCSFMO) and La0.70Ca0.1Sr0.2MnO3 (LCSMO), applicable for the magnetic cooling, have been explored. The X-ray diffraction patterns show that these samples are in single phase with rhombohedral structure. A remarkable decrease in the Curie temperature from 346 to 223 K was observed for 10% of Fe doping at Mn-site in the LCSMO sample. The substitution of Mn by Fe results in a combination of doping disorder, a site-percolation and Mn–Fe super-exchange interactions, which suppresses the ferromagnetism. The maximum magnetic entropy change of 1.53 J kg-1 K-1 with field variation of 3 T was obtained for the LCSFMO sample. The relative cooling power (RCP) ∼120 J kg-1 was found for an applied magnetic field of 3 T. The comparable magnetic entropy change and RCP values suggested that the studied samples have potential as a refrigerant for cooling applications.

• Synthesis and resistive switching behaviour of ZnMnO3 thin films with an Ag/ZnMnO3/ITO unsymmetrical structure

Single-phase MnZnO3 films were prepared on glass substrates coated with the use of indium tin oxide (ITO) as transparent bottom electrode via the sol–gel method. The effects of annealing temperature on structure, resistance switching behaviour and endurance characteristics of the ZnMnO3 films were investigated. The stable resistive switching behaviour with high resistance ratio in Ag/ZnMnO3/ITO unsymmetrical structure was observed. No second phase is detected, and the crystallinity of the MnZnO3 films is improved with the increase in annealing temperature from 350 to 400°C. The MnZnO3 films annealed at 350–450°C with an Ag/MnZnO3/ITO structure exhibit bipolar resistive switching behaviour. Ohmic and space-charge-limited conductions are the dominant mechanisms at low and high resistance states, respectively. $V{}_{\text{ON}},\ \text{V_{OFF}}$ and $R_{\text{HRS}}/R_{\text{LRS}}$ of theMnZnO3 films increase with the increase in annealing temperature. Improved endurance characteristics are observed in the samples annealed at 350 and 400°C. The endurance of the MnZnO3 films degrades when annealed at &gt;450°C.

• Short-range order of germanium selenide glass

Chalcogenide Ge20Se80 glass was prepared using the melt-quench technique. The radial distribution function is obtained from X-ray diffraction data in the scattering vector interval 0.28 ≤ 𝐾 ≤ 6.87 Å-1. ReverseMonte Carlo (RMC) simulations are useful to compute the partial pair distribution functions, $\text{g}_{ij} (r)$, partial structure factors, $S_{ij} (K)$, and total structure factor. Values of $r_{1}/r_{2}$ ratio and bond angle (𝛩) indicate that Ge(Se1/2)4 tetrahedra units connected by chains of the chalcogen atoms are present. The partial structure factors have shown that homopolar Ge–Ge and Se–Se bonds are behind the appearance of the first sharp diffraction peak (FSDP) in the total structure factor. Tetrahedral Ge(Se1/2)4 structural units connected by Se–Se chains have been confirmed by the simulated values of the partial coordination numbers and bond angle distributions. Finally, Raman spectra measurements have strongly supported the conclusions obtained either from the calculated Fourier data or from RMC simulations.

• Acoustic relaxation of some lead niobium tellurite glasses

The longitudinal ultrasonic attenuation in 𝑥Nb2O5 −(1−𝑥)TeO2, 0.1PbO−𝑥Nb2O5−(0.9−𝑥)TeO2 and 0.2PbO − 𝑥Nb2O5− (0.8−𝑥)TeO2 tellurite glass systems was measured using the pulse echo technique at ultrasonic frequencies 2, 4, 6 and 8 MHz in the temperature range from 150 to 300 K. The absorption curves showed the presence of well-defined broad peaks at various temperatures depending upon the glass composition and operating frequency. The maximum peaks move to higher temperatures with the increase of operating frequency, indicating the presence of some kind of relaxation process. This process has been described as a thermally activated relaxation process, which happens when ultrasonic waves disturb the equilibrium of an atom vibrating in a double-well potential in the glass network structure. Results proved that the average activation energy of the process depends mainly on the modifier content. This dependence was analysed in terms of the loss of standard linear solid type, with low dispersion and a broad distribution of Arrhenius-type relaxation with temperature-independent relaxation strength. The experimental acoustic activation energy has been quantitatively analysed in terms of the number of loss centres (number of oxygen atoms that vibrate in the double-well potential).

• Series-connected substrate-integrated lead-carbon hybrid ultracapacitors with voltage-management circuit

Cell voltage for a fully charged-substrate-integrated lead-carbon hybrid ultracapacitor is about 2.3 V. Therefore, for applications requiring higher DC voltage, several of these ultracapacitors need to be connected in series. However, voltage distribution across each series-connected ultracapacitor tends to be uneven due to tolerance in capacitance and parasitic parallel-resistance values. Accordingly, voltage-management circuit is required to protect constituent ultracapacitors from exceeding their rated voltage. In this study, the design and characterization of the substrate-integrated lead-carbon hybrid ultracapacitor with co-located terminals is discussed. Voltage-management circuit for the ultracapacitor is presented, and its effectiveness is validated experimentally.

• Cobalt oxide nanoparticle-modified carbon nanotubes as an electrocatalysts for electrocatalytic evolution of oxygen gas

A simple procedure was developed to prepare cobalt oxide nanoparticles (nano-CoO𝑥) on multiwall carbon nanotube-modified glassy carbon electrode (MWNT/GCE). Scanning electron microscopy revealed the electrodeposition of nano-CoO𝑥 with an average particle size of 25 nm onto MWNT/GCE. Also, the presence of nano-CoO𝑥 was revealed by energy dispersive X-ray spectra. The electrocatalytic activity of nano-CoO𝑥 and MWNT composite-modified GCE (CoO𝑥–MWNT/GCE) has been examined towards the oxygen evolution reaction (OER) by linear sweep voltammetry. The OER is significantly enhanced at CoO𝑥–MWNT/GCE, as demonstrated by a negative shift in the polarization curves at the CoO𝑥–MWNT/GCE compared with that obtained at the CoO𝑥–GCE and GCE. Optimization of the operating experimental conditions (i.e., solution pH and loading level of nano-CoO𝑥) has been achieved to maximize the electrocatalytic activity of CoO𝑥–MWNT/GCE. The maximum electrocatalytic activity towards the OER was obtained in alkaline media (pH = 13). The electrocatalytic activity of CoO𝑥–MWNT/GCE increased with the number of potential cycles employed for the CoO𝑥 deposition till a certain loading (20 cycles) beyond which an adverse effect is observed. The fabricated CoO𝑥–MWNT/GCE exhibited a good stability and durability. The value of energy saving per gram of oxygen gas at a current density of 10 mA cm-2 is 19.3 kWh kg-1.

• Synergetic action of doping and coating on electrochemical performance of lithium manganese spinel as an electrode material for lithium-ion batteries

Spinel LiMn2O4 and multidoped spinel LiMn1.9Co0.025Cr0.025Ni0.025Fe0.025O4 were synthesized by the glycine-nitrate method and coated with lithium borosilicate (LBS) in order to enhance the electrochemical performance at room temperature. The structure and electrochemical performance of all samples were characterized by inductively coupled plasma-mass spectrometer (ICP-MS), X-ray diffraction (XRD), differential thermal analysis/thermogravimetry (DTA/TG), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM) and galvanostatic charge–discharge measurements. The XRD analysis shows that the samples exhibit a pure spinel phase. The SEM results indicated that LBS particles had encapsulated the surface of the undoped and multidoped LiMn2O4 without causing any structural change. The charge–discharge tests showed that LiMn1.9Co0.025Cr0.025Ni0.025Fe0.025O4 displays better cycling performance than the pristine LiMn2O4 at room temperature. However, in the same conditions, LBS-coated LiMn1.9Co0.025Cr0.025Ni0.025Fe0.025O4 and LiMn2O4 have better cycling performance than uncoated samples. The results suggest that multidoped and LBS-coated LiMn2O4 could develop into a promising cathode material for lithium ion batteries.

• Electrochemical analysis on poly(ethyl methacrylate)-based electrolyte membranes

Polymer blend composed of poly(vinyl chloride) and poly(ethyl methacrylate) with lithium perchlorate (LiClO4) and the plasticizer ethylene carbonate (EC) mixture with propylene carbonate, 𝛾-butyrolactone (GBL), dibutyl phthalate and diethyl carbonate have been synthesized using the solution casting technique. Structural changes and thermal stability of the films were resolved using X-ray diffraction analysis and thermogravimetric/differential thermal analysis, respectively. The membrane that contains EC+ GBL exhibits maximum ionic conductivity of the order of 1.208×10-3 S cm-1 at 303 K. The temperature-dependent ionic conductivity of the polymer membranes has been estimated using AC impedance analysis.

• Characteristics of bulk liquid undercooling and crystallization behaviors of jet electrodeposition Ni–W–P alloy

The undercooling of Ni–W– P ternary alloy coating melt was investigated by in situ differential scanning calorimeter (DSC) with the flux processing technique. The results showed that the highest undercooling of Ni–W–P ternary alloy with 359 K was obtained as the thermal treatment temperature of themelt being 1679 K and the cooling rate being 50 K min-1. When cooling rate is fixed, the change of undercooling depends on the melt processing temperature, and the undercooling will increase rapidly at the first stage. The effects of thermal treatment temperature and cooling rates on the undercooling were discussed.

• A sensitive nonenzymatic hydrogen peroxide sensor based on Fe3O4–Fe2O3 nanocomposites

The Fe3O4–Fe2O3 nanocomposites were prepared by the co-precipitation method and followed by calcination process. The products were synthesized and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray analysis. The obtained Fe3O4–Fe2O3 nanocomposites were then applied to study the electrocatalytic reduction of hydrogen peroxide (H2O2) in 0.01 M pH 7.0 phosphate buffer medium. Then the Fe3O4–Fe2O3 nanocomposites were used as active electrode material of electrochemical sensors for H2O2 detection The detection sensitivity of the sensor was 20.325 𝜇A mM-1, and the detection limit was estimated to be about 0.2 mM.

• Multi-walled carbon nanotube-coated cotton fabric for possible energy storage devices

A conducting cotton fabric with a resistance of &lt;1.5 k𝛺 cm-2 was obtained by dip coating of multiwalled carbon nanotubes (MWCNTs) dispersed in a surfactant, sodium dodecyl sulphate (SDS). The dip coating was repeated up to 20 times to increase the loading of MWCNT as observed from optical absorption spectra (𝜆max = 442 nm). The field emission scanning electron microscopy (FE-SEM) image of coated fabric at different magnifications shows micro-fibril structure. Energy-dispersive X-ray analysis (EDXA) spectra show peaks for carbon and other constituent elements of SDS, Na and S. In order to improve the functionality of loaded MWCNT, the coated fabric was treated with 5% HNO3 for 3 h. For such a sample, the resistance decreased significantly to 1.5 k𝛺 cm-2, whereas it is 2.0 and 2.5 k𝛺 cm-2 for untreated and KOH-treated sample. This is in corroboration with 𝐼−𝑉 characteristics, and is attributed to increased loading of MWCNT through hydrogen bonding with glycosidic group present in cotton (cellulose) fibres. The series capacitance of the MWCNT-coated fabric is about 40 𝜇F cm-2, which is found to decrease with the increase in frequency, close to zero at about 20 kHz. A capacitor formed by placing two MWCNT-coated fabrics between etched PCB plates (terminal contacts) shows the charging capacity of about 1 F.

• Friction-reducing micro/nanoprotrusions on electrodeposited Ni–Co alloy coating surface fabricated by laser direct writing

Ni–Co coating or texturing surface has been studied extensively to improve the anti-friction ability of the surface. In this paper, we combine the advantages of Ni–Co coating and textured surface, and then use a simple, novel and easily controlled method to fabricate a series of micro/nanoprotrusions on the Ni–Co coating surface. The nanotribology properties were characterized by AFM. The result shows that the micro/nanotextured surface significantly reduced the friction forces compared with the original Ni–Co coating surface. The half-ellipsoid patterns have better tribology properties than half-hemispherical patterns. Both laser power and laser scanning speed were found to influence the friction performances.

• Analysis of P(VdCl-co-AN-co-MMA)-LiClO4-EC triblock copolymer electrolytes

The lithium ion conducting copolymer electrolytes based on poly(vinylidene chloride-co-acrylonitrileco- methyl methacrylate) P(VdCl-co-AN-co-MMA)-lithium per chlorate (LiClO4) (P(VdCl-co-AN-co-MMA): LiClO4) and poly(vinylidene chloride-co-acrylonitrile-co-methyl methacrylate)P(VdCl-co-AN-co-MMA)-lithium per chlorate (LiClO4)-ethylene carbonate (EC) (P(VdCl-co-AN-co-MMA):LiClO4:EC) of different compositions were prepared by solution-casting technique. Structural and surface morphological characterizations were studied by X-ray diffraction analysis and scanning electron microscopy measurements, respectively. Thermal and conductivity behaviour of copolymer–salt and copolymer–salt–plasticizer complexes were studied by employing differential scanning calorimetry and AC impedance measurements, respectively. The highest bulk conductivity was found to be 1.94 × 10-4 S cm-1 at 303 K for the plasticized sample. The dielectric behaviour and relaxation parameters of the samples have been presented and discussed.

• Fabrication of back contacts using laser writer and photolithography for inscribing textured solar cells

Semiconductor fabrication process begins with photolithography. Preparing a photo mask is the key process step in photolithography. The photo mask was fabricated by inscribing patterns directly onto a soda lime glass with the help of a laser beam, as it is easily controllable. Laser writer LW405-A was used for preparing the mask in this study. Exposure wavelength of 405 nm was used, with which 1.2 𝜇m feature size can be written in direct write-mode over the soda lime glass plate. The advantage of using the fabricated mask is that it can be used to design back contacts for thin film Photovoltaic (PV) solar cells. To investigate the process capability of LW405-A, same pattern with different line widths was written on soda lime glass samples at different writing speeds. The pattern was inscribed without proximity effect and stitching errors, which was characterized using optical microscope and field emission scanning electron microscope (FE-SEM). It was proven that writing speed of a mask-writer is decided according to the intended feature size and line width. As the writing speed increases, the edges of the patterns become rougher due to uneven scattering of the laser beam. From the fabricated mask, the solar cell can be developed embedding both the contacts at the bottom layer, to increase the absorption of solar radiation on the top surface effectively by increasing light absorption area.

• Characterization of electroless nickel as a seed layer for silicon solar cell metallization

Electroless nickel plating is a suitable method for seed layer deposition in Ni–Cu-based solar cell metallization. Nickel silicide formation and hence contact resistivity of the interface is largely influenced by the plating process and annealing conditions. In the present work, a thin seed layer is deposited from neutral pH and alkaline electroless nickel baths which are annealed in the range of 400–420°C for silicide morphology and contact resistivity studies. A minimum contact resistivity of 7 m𝛺 cm2 is obtained for seed layer deposited from alkaline bath. Silicide formation for Pd-activated samples leads to uniform surface morphology as compared with unactivated samples due to non-homogeneous migration of nickel atoms at the interface. Formation of nickel phosphides during annealing and the presence of SiO2 at Ni–Si interface creates isolated Ni2Si–Si interface with limited supply of silicon. Such an interface leads to the formation of high resistivity metal-rich Ni3Si silicide phase which limits the reduction in contact resistivity.

• Effects of metal doping on photoinduced hydrophilicity of SnO2 thin films

The influence of metal dopants (Mn2+, Al3+ and Cu2+) on the wetting properties of SnO2 thin films deposited by thermal evaporation is reported. The undoped and doped SnO2 films crystallize into the orthorhombic structure upon annealing at 200°C for 110 h. It is shown that wettability behaviour, before and after ultraviolet (UV) irradiation, is dependent on the ionic radius of the dopant. The contact angle of un-irradiated samples increases with increase in ionic radius of the dopant and also in comparison with the undoped sample. It is 54° for pure SnO2 and increases to 77.5°, 92.3° and 95.9° for the Al3+, Mn2+ and Cu2+ doped samples, respectively. After UV irradiation, the value is 5.4° for the undoped sample. This increases to 21.2° for Al doping reaching a minimum of 6.4° for the Mn-doped sample increasing thereafter to 63.3° for the Cu-doped sample. It is observed that pre-irradiation contact angle behaviour can be correlated with the change in roughness of the films with increasing ionic radius. In contrast, photoinduced hydrophilicity of the films correlates with their optical bandgap. The contact angle is lowest for the lowest bandgap material, i.e., Mn-doped SnO2, with a bandgap of 2.48 eV. Thus, the band structure of SnO2 that can be controlled by dopant ionic radius can in turn be employed to manipulate the wettability of these surfaces.

• Electrospun TiO2 nanofibre-based gas sensors fabricated by AC electrophoresis deposition

In this paper, gas sensing properties of the sensor based on titanium dioxide (TiO2) nanofibres are reported. These nanofibres were synthesized through electrospinning of polyvinyl pyrrolidone (PVP) / titanium tetra isopropoxide. Calcination of the obtained amorphous PVP/TiO2 nanofibres resulted in nanofibres of TiO2 with the same morphology. In this step, scanning electron microscopy and X-ray diffraction were applied in order to analyse these nanofibres. Then, nanofibres of TiO2 were deposited selectively by AC electrophoretic deposition on interdigitated electrodes and exposed to different concentrations of NO2 (8–50 p.p.m.) at 450–550°C. Gas sensing measurements illustrated that this sensor had adequate response to target gas at 450°C. The maximum response of gas sensors, 𝑆 (the ratio of sensor resistances $S = R_{\text{gas}}/R_{\text{N2}}$), achieved was around 30 for 50 p.p.m. NO2 at 450°C.

• Facile combustion synthesis of novel CaZrO3:Eu3+, Gd3+ red phosphor and remarkably enhanced photoluminescence by Gd3+ doping

A facile sol–gel combustion route was reported for the direct preparation of CaZrO3:Eu3+ and CaZrO3:Eu3+, Gd3+. The obtained deposits were characterized by XRD, TGA-DSC, SEM, EDS, PL measurements and microscope fluorescence. When the Gd3+ ions were introduced in this compound, the emissions of CaZrO3:Eu3+ were remarkably enhanced. The emission spectrum of CaZrO3:Eu3+, Gd3+ nanocrystals exhibited a red shift compared with CaZrO3:Eu3+ samples. A new mechanism of the improved photoluminescent properties of Eu3+ by Gd3+ was investigated. The optimized phosphor CaZrO3:5%Eu3+, 2%Gd3+ could be considered an efficient red-emitting component for white lighting devices excited in the near-ultraviolet region.

• Analytical calculation of chain length in ferrofluids

The response of a typical ferrofluid (FF) lies in its explicit property of chain formation of magnetic nanoparticles. The most significant magneto-optic (MO) and magneto-viscous (MV) effects of FF are attributed to chaining effect. In the present research, an effort was made to analytically justify the dependence of the structure evolution of FFs on different measurable parameters involved in MO and MV effects. The problem is treated with the help of dimensional analysis and an empirical relation is formulated relating the equilibrium chain length with Verdet coefficient (constant), particle diameter, viscosity of the carrier fluid, particle density, magnetization and shear rate. The formulated relation of chain length is supported by error analysis to yield the uncertainty in the result. The maximum uncertainty in four sets of data is found as ∼0.75.

• Photocatalytic activity of Ce-modified SBA-15 for the degradation of isoproturon

Cerium (Ce)-modified SBA-15 and Al-grafted SBA-15 are prepared and compared their photocatalytic activity for isoproturon degradation. The Al-SBA-15 is prepared by postsynthetic grafting method and cerium-modified samples are prepared by the impregnation technique. All the samples are characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and N2 adsorption/desorption analysis. The samples show well-ordered mesoporous structure and it is confirmed by XRD. The UV–vis DRS of Cemodified sample shows a red shift compared to SBA-15 and the cerium species are stabilized in +3 oxidation state at lower cerium contents. The presence of Ce3+ species is also substantiated by XPS analysis. The higher amount of Ce3+ species are accompanied by oxygen vacancies which are formed due to the contact of ceria with the support. The N2 adsorption/desorption analysis of the samples show type-IV isotherms characteristic of mesoporous materials. Photocatalytic activity evaluation studies are made on all the samples for the degradation of isoproturon. Among them, 0.3 (wt%) Ce-modified Al-SBA-15 catalyst has shown a maximum activity in comparison with Ce-modified SBA-15. The better activity is attributed to the synergistic effect of mesoporosity and the presence of Ce3+ species along with oxygen vacancies.

• Electroluminescence and negative differential resistance studies of TPD:PBD:Alq3 blend organic-light-emitting diodes

Ternary system of single-layer organic-light-emitting diodes (OLEDs) were fabricated containing tris(8-hydroxyquinoline) aluminium (Alq3) blended with N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole small molecules. Electroluminescence properties were investigated with respect to blend systems. Significant improvement in turn-on voltage and luminance intensity was observed by employing the blends technique. Negative differential resistance (NDR) characteristics observed at a low voltage region in blended OLED is related to the generation of guest hopping site and phonon scattering phenomenon. However, luminescence of the devices is not altered by the NDR effect.

• Ultrasonic investigations of some bismuth borate glasses doped with Al2O3

The velocities of longitudinal and transverse ultrasonic waves in different compositions of 5Al2O3–29Na2O–(66−𝑥)B2O$_{3}−x$Bi2O3 glass system were measured at 4 MHz at room temperature using the pulse-echo technique. The velocity data were used to determine the elastic moduli and the dimensionality of the studied glasses. The observed changes in the elastic moduli of the glasses were related to the modifier role of Bi2O3 content. The results revealed that the density increased with increasing Bi2O3 content, which was attributed to the increase in the compactness and packing of the glass network. The ultrasonic data were analysed in terms of creation of new bonds of Bi2O3 attached to the structural units of the borate network. The new bonds decreased the average crosslink density and the number of network bonds per unit volume along with a weakening of the different modes of vibrations, which in its turn decreased the ultrasonic velocity. Quantitative analysis was carried out using Makishima–Mackenzie model in order to obtain more information about the rigidity of these glasses.

• Influence of thermo-mechanical processing on microstructure, mechanical properties and corrosion behavior of a new metastable 𝛽-titanium biomedical alloy

This paper presents the results on the influence of different thermo-mechanical processing (TMP) on themechanical properties and electrochemical behavior of newmetastable 𝛽-alloy Ti–20.6Nb–13.6Zr–0.5V (TNZV). TMP included hot working in below 𝛽-transus, solution heat treatments at same temperature in different cooling rates in addition to aging. Depending upon the TMP conditions, a wide range of microstructures with varying spatial distributions and morphologies of equiaxed/elongated 𝛼, 𝛽 phases were attained, allowing for a wide range of mechanical and electrochemical properties to be achieved. The corrosion behavior of studied alloy was evaluated in Ringer’s solution at 37°C using open-circuit potential-time and potentiodynamic polarization measurements.

• Biphasic calcium phosphate–casein bone graft fortified with Cassia occidentalis for bone tissue engineering and regeneration

Research on traditional herbs is gaining momentum owing to their potent medical properties, among which Cassia occidentalis (CO) is a promising herb, with osteogenic potential. The study investigates the efficacy of CO extract incorporated biphasic calcium phosphate as an osteoinductive material. Prepared bone implants were characterized physico-chemically using FT-IR, TGA, XRD, SEM and EDX. The implants were analysed further for mechanical and biological properties. The results revealed that CO extract-incorporated bone implants possessed better compression strength and it was able to induce proliferation and enhance alkaline phosphatase activity in SaOS-2 cells. The implant proves to be promising for bone tissue engineering, and hence it demands further in vivo evaluation.

• Simple fabrication of Ag nanoparticle-impregnated electrospun nanofibres as SERS substrates

A facile method for the fabrication of electrospun polyurethane (PU) nanofibres impregnated with Ag nanoparticles (NPs) as an efficient and free-standing surface-enhanced Raman scattering (SERS) substrates is reported here. Electrospinning was used to produce polymeric nanofibrous matrix, while a liquid polyol(ethylene glycol) solvent under low temperature was used not only to reduce Ag+ to Ag0, but also was employed as the in situ growth medium for well-dispersed Ag NPs on the surface of fibre nets. Large enhancement in Raman signals of 4-mercaptobenzoic acid analytes could be realized in the present Ag/PU nanofibres due to the presence of SERS ‘hotspots’ by means of appropriate interparticle gap.

• Cost effective and shape controlled approach to synthesize hierarchically assembled NiO nanoflakes for the removal of toxic heavy metal ions in aqueous solution

Hierarchical mesoporous NiO nanoflakes (NiOs) have been synthesized in high yield via a simple, economical and environmentally friendly hydrothermal route. The as-prepared NiOs were characterized by powder X-ray diffraction (PXRD), scanning electronicmicroscopy (SEM), transmission electronmicroscopy (TEM), selected area electron diffraction patterns (SAED), X-ray energy dispersive spectroscopy (EDS) and nitrogen adsorption–desorption techniques (Brunauer–Emmett–Teller, BET). Adsorption of heavy metal ions onto the as-prepared sample from aqueous solutions was investigated using differential pulse anodic stripping voltametry (DPASV) technique and discussed. The product possesses a BET surface area of 69.27 m2 g-1. It is found that NiOs exhibited the excellent performance for the removal of Hg(II), Pb(II) and Cd(II) from aqueous solution. The equilibrium adsorption data of Hg(II), Pb(II) and Cd(II) on the as-prepared NiOs were analyzed by Langmuir and Freundlich models, suggesting that the Langmuir model provides the better correlation of the experimental data. The adsorption capacities for removal of Hg(II), Pb(II) and Cd(II) were determined using the Langmuir equation and found to be 1324.5, 1428.9 and 1428.5 mg g-1, respectively. Adsorption kinetics of all the metal ions followed pseudo second-order model. Moreover, NiOs can be recycled by simple acid treatment, which could retain the high removal efficiency in three successive cycles. This study suggests that nanoflakes could be explored as a new adsorbent with high efficiency and recyclability for removing heavy metal ions from aqueous solution.

• # Bulletin of Materials Science

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Volume 42 | Issue 5
October 2019

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Posted on July 25, 2019

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