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      Volume 39, Issue 7

      December 2016,   pages  1619-1889

    • Luminescence properties of terbium-doped Li$_3$PO$_4$ phosphor for radiation dosimetry

      C B PALAN N S BAJAJ S K OMANWAR

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      A polycrystalline sample of Li$_3$PO$_4$:Tb$^{3+}$ phosphor was successfully synthesized using solid-state diffusion method. This synthesis method is of low cost, low temperature and does not require any other atmospheres for the synthesis. The powder X-ray diffraction (PXRD), photoluminescence (PL) emission and excitation spectra, thermoluminescence (TL) and optically stimulated luminescence (OSL) were measured. The particle size was calculated using the Debye Scherrer formula and found to be 79.42 nm. PL emission spectra of Li$_3$PO$_4$:Tb$^{3+}$ phosphor show the strong prominent peak at 544 nm corresponding to ${}^{5}$D$_4$ to ${}^{7}$F$_5$ transitions of Tb$^{3+}$. The OSL sensitivity of prepared Li$_3$PO$_4$:Tb$^{3+}$ phosphor was 50% of that of $\alpha$-Al$_2$O$_3$:C. Its decay curve consists of three components withphotoionization cross-sections $0.44\times 10^{−17}$, $3.09\times 10^{−17}$ and $23\times 10^{−17}$ cm$^{2}$. The TL glow curve of the prepared sampleconsists of two characteristic peaks, which were deconvoluted using the peak fit software, and kinetic parameters were determined using the peak shape method. TL intensity was compared with that of the commercially availableTLD-500 phosphor. OSL dose response was linear in the measured range and the minimum detectable dose (MDD) was found to be 67.42 $\mu$Gy, while fading of the OSL signal was found to be about 27% in 4200 min after which theOSL signal stabilizes.

    • Contents

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    • Near-infrared spectral downshifting in Sr$_{(3−x)}$(VO$_4$)$_2$:${}_x$Nd$^{3+}$ phosphor

      N S SAWALA K A KOPARKAR N S BAJAJ S K OMANWAR

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      In this study, the spectral downshifting (DS) from ultraviolet (UV) light to near-infrared (NIR) radiation in Sr$_3$(VO$_4$)$_2$:Nd$^{3+}$ phosphor is reported. The prepared materials were characterized by X-ray powder diffraction(XRD) and photoluminescence (PL) properties along with steady state luminescence time decay curves were studied, which confirmed the energy transfer (ET) from VO$_4^{3−}$ ions to Nd$^{3+}$ ions. The DS phenomenon by phosphor was observed, which involved emission of NIR photons (1075 and 1064 nm) and visible photons (506 nm) from absorbed UV photons at 349 nm. The theoretical energy transfer efficiency (ETE) was calculated with the help of steady state luminescence time decay curves and the maximum ET efficiency approached up to 41.33%. The crystalline silicon (c-Si) cell has maximum efficiency in NIR region of solar spectrum due to an energy band gap of 1.12 eV.Sr$_3$(VO$_4$)$_2$:Nd$^{3+}$ can be potentially used as a NIR DC phosphor for c-Si solar cells.

    • Crystal structure of the new diamond-like semiconductor CuMn$_2$InSe$_4$

      G E DELGADO V SAGREDO

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      The crystal structure of the semiconductor compound CuMn$_2$InSe$_4$ was analysed using X-ray powder diffraction data. CuMn$_2$InSe$_4$ crystallizes, with a stannite structure, in the tetragonal space group I$\bar{4}$2m (No. 121), $Z = 2$, with unit cell parameters $a = 5.8111(2) \AA$, $c = 11.5739(8) \AA$ and $V = 390.84(3) \AA^#$. The refinement of 28 instrumental and structural parameters led to $R_{\rm p} = 8.1$%, $R_{\rm wp} = 10.5$%, $R_{\rm exp} = 6.5$% and $S = 1.6,$ for 86 independent reflections.

    • Optimization of CVD parameters for long ZnO NWs grown on ITO/glass substrate

      ABDULQADER D FAISAL

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      The optimization of chemical vapour deposition (CVD) parameters for long and vertically aligned (VA) ZnO nanowires (NWs) were investigated. Typical ZnO NWs as a single crystal grown on indium tin oxide (ITO)-coated glass substrate were successfully synthesized. First, the conducted side of ITO–glass substrate was coated with zinc acetate dihydrate to form seed layer of ZnO nanocrystals. Double zone tube furnace connected to vacuum pump was used for ZnO growth process. Zn metal powder was positioned at the first zone at temperature 900$^{\circ}$C. The ITO–glass substrate with pre-coated seed layer was then located in the second zone of tube furnace at growth temperature of 550$^{\circ}$C. The growth of ZnO NWs was controlled under constant concentration of seed layer, while other parameters such as argon and oxygen flow rates, substrate position, time and oxygen flow rate were varied.The VA ZnO NWs were finally characterized by scanning electron microscopy, X-ray diffractometer and high-resolution transmission electron microscope equipped with energy-dispersive X-ray spectroscopy. The results showthat long and VA ZnO NWs were single crystalline with hexagonal wurtzite structure. The ultimate length and average diameter of ZnO NWs were 10 $\mu$m and 50–100 nm, respectively. These were achieved under optimized CVD growth parameters. The mechanism of vertical growth model of ZnO NWs is also discussed.

    • Sintering behaviour and microwave dielectric properties of a new complex perovskite: ($1−x$)(Sr$_{0.3}$Ca$_{0.427}$Nd$_{0.182}$)TiO$_{3−x}$SmAlO$_3$ ceramics

      JING JING QU FEI LIU XING WEI CHANG LAI YUAN XIAN PEI HUANG

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      Structural features and microwave dielectric properties of ($1−x$)(Sr$_{0.3}$Ca$_{0.427}$Nd$_{0.182}$)TiO$_{3−x}SmAlO$_{3}($0.05 \le x \le 0.4$) ceramics were investigated. X-ray diffraction patterns illustrated that solid solutions with the orthorhombic perovskite were shown to be formed in the ranges of $0.05 \le x \le 0.4$. Moreover, the dielectric constant ($\epsilon_r$) of sintered ceramics had a quasi-linear decrease with the increase in SmAlO$_3$ content. A certain amount of Sm and Al substitution for A- and B-sites could substantially improve the quality factor ($Qf$) of the ceramics. Increasing the oxygen octahedral distortion led to a decrease in the temperature coefficient of the resonant frequency ($\tau_f$) from 216.3 to $−$34.8 ppm $^{\circ}$C$^{−1}$. Additionally, optimized microwave dielectric properties can be achieved for the specimens using 0.75(Sr$_{0.3}$Ca$_{0.427}Nd$_{0.182}$)TiO$_3$–0.25SmAlO$_3$ ceramics [$\epsilon_r \sim 58.3$, $Qf \sim 18800$ GHz (at 4.65 GHz) and$\tau_f \sim 2.3$ ppm $^{\circ}$C$^{−1}$] after being sintered at 1500$^{\circ}$C for 4 h.

    • Characterization of Fe$^{3+}$-doped silver phosphate glasses

      B P CHOUDHARY N B SINGH

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      The relationship among the composition, structure and selected properties for five series of silver phosphate glasses containing 0, 5, 10, 15 and 20wt% Fe$_2$O$_3$ has been investigated. The synthesized glasses have been characterized using different experimental techniques. X-ray diffraction studies revealed that the glasses are amorphous in nature. IR spectral studies have shown the presence of characteristic P–O–P linkages of linear phosphate chains,presence of O–P–O units in the phosphate tetrahedral and the formation of P–O–Fe bonds in the doped glass. It is also confirmed that due to doping of Fe$_2$O$_3$, loosening of glassy structure occurred and the glass became more disordered. Differential scanning calorimetric (DSC) studies revealed that glass transition temperature increased with Fe$_2$O$_3$ concentration. Scanning electron microscopic studies have shown that Fe$_2$O$_3$ doping modifies the microstructures of the glass and at lower concentration of dopant, a nanostructure is obtained. Electrical conductivity measurements from 303 to 373 K in a frequency range from 100 Hz to 5 MHz have indicated that all glasses are ionic conductors with Ag$^+$ ions as the charge carrier. Fe$_2$O$_3$ doping in silver phosphate glass increased the electrical conductivities. Results have shown that dielectric constants increased with the increase of temperature at all the frequencies; a.c. and d.c. conductivities have been separated and a Cole–Cole plot is also drawn. Dielectric losses in all the glasses decreased with frequency at a particular temperature. It is found that Ag$_2$O–P$_2$O$_5$ glass doped with 5wt% Fe$_2$O$_3$ gives high OCV value and the doped glass can be used as an electrolyte for solid-state batteries.

    • Effects of Zn doping concentration on resistive switching characteristics in Ag/La$_{1−x}Zn$_x$MnO$_3$/p$^+$-Si devices

      SHUAISHUAI YAN HUA WANG JIWEN XU LING YANG WEI QIU QISONG CHEN DONG HAN

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      Ag/La$_{1−x}$Zn$_x$MnO$_3$/p$^+$-Si devices with different Zn doping contents were fabricated through sol–gel method. The effects of Zn doping concentration on the microstructure of La$_{1−x}$Zn$_x$MnO$_3$ films, as well as on the resistance switching behaviour and endurance characteristics of Ag/La$_{1−x}$Zn$_x$MnO$_3$/p$^{+}$-Si were investigated. After annealing at 600$^{\circ}$C for 1~h, the La$_{1−x}$Zn$_x$MnO$_3$ ($x = 0.1$, 0.2, 0.3, 0.4, 0.5) are amorphous and have bipolar resistance characteristics, with RHRS/RLRS ratios $>$103. However, the endurance characteristics show considerable differences; $x = 0.3$ shows the best endurance characteristics in more than 1000 switching cycles. The conduction mechanism of the Ag/La$_{1−x}$Zn$_x$MnO$_3$/p$^{+}$-Si is the Schottky emission mode at high resistance state. However, the conduction mechanism at low resistance state varies with Zn doping concentration. The dominant mechanism at $x = 0.1$ is filamentary conduction mechanism, whereas that at $x \ge 0.2$ is space-charge-limited current conduction.

    • Morphological and optical properties of n-type porous silicon: effect of etching current density

      M DAS D SARKAR

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      Morphological and optical properties of porous silicon (PS) layer fabricated on n-type silicon wafer have been reported in the present article. Method of PS fabrication is by photo-assisted electrochemical etching with different etching current densities ($J$). Porosity and PS layer thickness, obtained by the gravimetric method, increase with increasing $J$. Pore morphology observed by FESEM shows the presence of randomly distributed pores with mostly spherical shape. Calculated pore size is also seen to increase with increasing value of $J$. XRD gives the characteristic amorphous peak of PS along with some peaks corresponding to crystalline silicon (c-Si). Calculated crystallite size shows decreasing trend with increasing $J$ value. The optical properties of these samples have been investigated by UV–visible reflectance, Raman spectroscopy and photoluminescence (PL) spectra. Reflectance measurement shows blue-shift of the spectrum with increased reflectivity for increasing $J$. Raman spectra show remarkable blue-shift with respect to the c-Si peak. PL spectra give the luminescence energy in the orange–red region of the visible spectrum and little change with variation of $J$.

    • Effect of temperature on the characteristics of ZnO nanoparticles produced by laser ablation in water

      ELMIRA SOLATI DAVOUD DORRANIAN

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      Effect of the water temperature on the characteristics of zinc oxide nanoparticles (NPs) produced by laser ablation process is investigated experimentally. The fundamental wavelength of a Q-switched Nd:YAG laserwas employed to irradiate a high-purity zinc plate in distilled water at different temperatures of 0, 20, 40 and 60$^{\circ}$C. The produced NPs were diagnosed by UV–vis–NIR spectroscopy, X-ray diffraction method, transmission electronmicroscopy and scanning electron microscopy. Results show that with increase in the water temperature from 20 to 60$^{\circ}$C, size of NPs decreases while their bandgap energy increases. Maximum ablation rate occurs at the highesttemperature. Crystalinity also increases with increase in the water temperature. The abnormal behaviour of water at 0–4$^{\circ}$C affects the NPs characteristics.

    • Effect of stabilizer on the morphology of Au@TiO$_2$ spheres: a combined experimental and theoretical study

      JIAN QI XUECHAO GAO QUAN JIN

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      In this study, two different particle sizes of Au nanoparticles (NPs) were synthesized using two different stabilizers, and then two different morphologies Au@TiO$_2$ hollow spheres were obtained when the corresponding Au NPs solutions were added to the TiF$_4$ ethanol–water solution under hydrothermal condition. The computational simulation is employed to provide the fundamental support to explain why different stabilizers yield different sizes of Au NPs, and the main cause for the experimental observation is contributed by the different interactive forces between Au and stabilizer molecules. The experimental strategy adopted different stabilizer in this work is expected to be generally applicable for the synthesis of many other types of micro-nanostructured materials.

    • Corrosion and wear behaviour of multilayer pulse electrodeposited Ni–Al$_2$O$_3$ nanocomposite coatings assisted with ultrasound

      H MAJIDI M ALIOFKHAZRAEI A KARIMZADEH A SABOUR ROUHAGHDAM

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      In this study, the Ni/Al$_2$O$_3$ nanocomposite multilayer coatings with six consecutive layers were electrodeposited on the mild steel by pulse electrodeposition with ultrasound agitation from nickelWatts-type bath. Thestructure and morphology of the etched coatings cross-section were characterized by scanning electron microscopy (SEM). The corrosion behaviour of these coatings was investigated in 1 M H$_2$SO$_4$ solution. All of the coatings showed the active–passive transition and the distinct difference in structure had negative influence on their corrosion resistance. Moreover, the tribological behaviour of these coatings was evaluated by pin-on-disc type. The results showed that wear resistance increased with increase in duty cycle and frequency.

    • Preparation and characterization of GA/RDX nanostructured energetic composites

      YUANFEI LAN XUEBAO WANG YUNJUN LUO

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      Graphene aerogel (GA) with nano-porous structure was assembled through the formation of physical cross-links between graphene sheets by a facile sol–gel method and supercritical CO$_2$ drying process. Thenhexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was added and trapped in the nano-porous three-dimensional networks of GA to obtain a novel GA/RDX nanostructured energetic composite. The composition, morphology andstructure of the obtained GA/RDX nanostructured energetic composite were characterized by elemental analysis, scanning electron microscopy, nitrogen sorption tests and X-ray diffraction. Moreover, the thermal decompositioncharacteristic was investigated by thermogravimetry and differential scanning calorimetry. The results showed that GA could be a perfect aerogel matrix for the fabrication of GA/RDX nanostructured energetic composite due to itsunique nano-porous structure and attributes. It was also demonstrated that RDX homogeneously disperses in the asprepared GA/RDX nanostructured energetic composite at nanometric scale. GA showed promising catalytic effects for the thermal decomposition of RDX. After incorporating with GA, the decomposition of RDX was obviously accelerated.

    • Synthesis, characterization and isotherm studies of new composite sorbents

      E S ZAKARIA I MALI M KHALIL T Y MOHAMED A EL-TANTAWY

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      With different methods, different molar ratios and different surfactants have been investigated to reach the optimum conditions for synthesized zirconium tungstate (Zr(IV)W). Zr(IV)W with different molar ratios of o-toluidinewas synthesized to reach the optimum conditions for poly-o-toluidine zirconium tungstate (POTZr(IV)W). POTZr(IV)W with different molar ratios of tungstate was used to achieve the optimum conditions for poly-otoluidine Zr(IV) tungstophosphate (POTZr(IV)WP). The Na$^+$ capacity for all the prepared materials was investigated in order to determine the best ion exchanger towards the absorbed ions. The chemical and physical propertiesof materials were determined. Sorption isotherm studies of La$^{3+}$, Ce$^{3+}$, Nd$^{3+}$ and Sm$^{3+}$ ions were performed at differentreaction temperatures and analysed by Langmuir, Freundlich, Dubinin–Raduchkivich and Temkin isotherm models. Thermodynamic parameters such as $\Delta$G$^{\circ}$, $\Delta$H$^{\circ}$ and $\Delta$S$^{\circ}$ were determined and found to be endothermic and spontaneous in nature.

    • Synthesis, characterisation and non-isothermal degradation kinetics of novel poly(mono ethylene glycol dimethacrylate-co-4-aminobenzoate)

      A JANCIRANI V KOHILA B MEENARATHI A YELILARASI R ANBARASAN

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      Synthesis of a novel co-polymer made by the addition polymerisation between MEGDMA and 4-AB by aza-Michael addition (AMA) polymerisation method is a fascinating field of research. The present investigationyielded a hazardous metal catalyst-free and toxic solvent-free methodology. The AMA polymerisation was carried out at five different [$M_1/M_2$] values under N$_2$ atmosphere at 100$^{\circ}$C for 2 h. Thus, obtained co-polymer was characterized by Fourier transform infrared spectroscopy, UV–visible reflectance spectroscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy (SEM). The SEM image confirmed the formation of polymer nanoparticles. The non-isothermal degradation kinetics was followed with four different models, such as Flynn-Wall-Ozawa, Auggis-Bennet, Kissinger and Friedman method. Among the modelsused, the Kissinger method yielded the lowest degradation kinetics. The degradation kinetics of the co-polymer was followed with the help of model-free methods. Moreover, it was critically compared with the literature.

    • Photocatalytic degradation of Malachite Green dye by modified ZnO nanomaterial

      S MEENA DIPTI VAYA B K DAS

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      In this article we report a chemical sol–gel approach to synthesize zinc oxide nanomaterials capped with ethylene diamine tetra acetic acid (EDTA), citric acid and oleic acid, and to study the effect of the surface modification on their photocatalytic activity and the kinetics for the degradation of Malachite Green (MG) dye. The structural, optical and chemical features were systematically characterized by X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared and UV–vis absorption spectroscopy. The objective of using the capping agents was to confine the size and control the growth and morphology of the nanomaterial. The smallest crystallite size was recorded as 29 nm for EDTA-capped rod-shaped ZnO. A comparison study of the effect of thethree different capping surfactants on ZnO nanomaterial for photocatalytic degradation ofMGdye under solar light showed that EDTA with higher denticity coordinated efficiently with the surface of ZnO nanocrystalline catalystsand hence demonstrated better decolouration of the dye under solar light. The dye degradation followed the psuedofirst-order kinetics. EDTA proved to be the best capping agent among all the three for ZnO nanomaterial.

    • Influence of ZnO concentration on the optical and photocatalytic properties of Ni-doped ZnS/ZnO nanocomposite

      W WANKU S O B OPPONG S K SHUKLA P P GOVENDER

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      Photocatalysts consisting of nickel-doped ZnS/ZnO core shell nanocomposites with varying concentrations of ZnO was synthesized through chemical precipitation method. The catalyst was deployed in photocatalyticdegradation of indigo carmine dye as a model organic pollutant. Characterization of the samples was achieved through the use of X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, UV–vis spectroscopy and energy dispersive spectroscopy. The composites consist of wurtzite ZnO phase deposited on cubic ZnS. Optical absorption, crystallite sizes and photocatalytic degradation efficiency increased with increasing ZnO concentration. Bandgap values of ZnS also decreased appreciably with increase in ZnO concentration. Ni-doped ZnS/(0.5 M ZnO) was identified as the most efficient catalyst with 91% dye degradation efficiency at a rate of $15.38 \times 10^{−3}$ min$^{−1}$ in 180 min. Meanwhile, the pristine ZnSdegraded 25% of the dye at the rate of $1.53×10^{−3}$ min$^{−1}$ within the same time. The Ni-doped Zn$ /(0.5 M ZnO) was used to degrade the dye on the basis of influence of factors such as solution temperature, hydrogen peroxide (H$_2$O$_2$) and ethanol contents. Dye degradation increased with increase in temperature, but decreased with ethanol content. H$_2$O$_2$ content initially caused enhanced dye degradation but the efficiency decreased with higher H$_2$O$_2$ content.

    • Influence of boron doping on mechanical and tribological properties in multilayer CVD-diamond coating systems

      SAJAD HUSSAIN DIN M A SHAH N A SHEIKH K A NAJAR K RAMASUBRAMANIAN S BALAJI M S RAMACHANDRA RAO

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      Titanium alloy (Ti6Al4V) substrates were deposited with smooth multilayer coatings, by hot filament chemical vapour deposition technique. The effect of boron doping on lattice parameter, residual stresses, hardness and coefficient of friction in multilayer-diamond coating system was studied. The frictional behaviour of the coatings was studied using a ball-on-disc micro-tribometer by sliding the coated samples of titanium alloy (Ti6Al4V) substrates against alumina (Al$_2$O$_3$) balls, and increasing normal load from 1 to 10N. The average friction coefficient decreased from 0.36 to 0.29 for undoped multilayer-diamond coating system and from 0.33 to 0.18 for borondoped (BD) multilayer-diamond coating system. The average indentation depths for undoped and BD multilayerdiamond coating systems were found to be equal to $\sim$58 and $\sim$65 nm, respectively, and their hardness values were 60 and 55~GPa, respectively.

    • Erratum to: Influence of boron doping on mechanical and tribological properties in multilayer CVD-diamond coating systems

      SAJAD HUSSAIN DIN M A SHAH N A SHEIKH K A NAJAR K RAMASUBRAMANIAN S BALAJI M S RAMACHANDRA RAO

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      In the online version of this article initially published, figure 1b was represented incorrectly. Figure 1b in the article has been corrected and republished.

    • Structural, optical spectroscopy, optical conductivity and dielectric properties of BaTi$_{0.5}$(Fe$_{0.33}$W$_{0.17}$)O$_{3}$ perovskite ceramic

      FAYÇAL BOURGUIBA AHMED DHAHRI TAREK TAHRI KAMEL TAIBI JEMAI DHAHRI E K HLIL

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      Fe and W co-substituted BaTiO3 perovskite ceramics, compositional formula BaTi$_{0.5}$(Fe$_{0.33}$W$_{0.17}$)O$_3$, were synthesized by the standard solid-state reaction method and studied by X-ray diffraction, scanning electronmicroscopy and spectroscopy ellipsometry. The prepared sample remains as double phases with the perovskite structure. The structure refinement of BaTi$_0.5$(Fe$_{0.33}$W$_{0.17}$)O$_3$ sample was performed in the cubic double and hexagonal setting of the Fm$\bar{3}$m and P6$_3$/mmc space groups. Spectral dependence of optical parameters; real and imaginaryparts of the dielectric function, refractive index, extinction coefficient and absorption coefficient were carried out in the range between 1.4 and 4.96 eV by using the ellipsometry experiments. Direct bandgap energy of 4.36 eV was found from the analysis of absorption coefficient vs. photon energy. In addition, the oscillator energy, dispersion energy and zero-frequency refractive index values were found from the analysis of the experimental data usingWemple–DiDomenico single-effective-oscillator model.

    • Structural, optical and morphological studies of undoped and Zn-doped CdSe QDs via aqueous route synthesis

      N THIRUGNANAM D GOVINDARAJAN

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      Undoped and Zn-doped CdSe quantum dots (QDs) were successfully synthesized by the chemical precipitation method. The structural, optical and morphological properties of the synthesized undoped and Zn-dopedCdSe QDs were studied by X-ray diffraction (XRD), UV–visible absorption spectroscopy, photoluminescence (PL) spectroscopy, fluorescence lifetime spectroscopy, scanning electron microscopy (SEM), field emission transmissionelectron microscopy (FE-TEM) and FTIR. The synthesized undoped and Zn-doped CdSe QDs were in cubic crystalline phase, which was confirmed by the XRD technique. From the UV–visible absorption spectral analysis, theabsorption wavelengths of both undoped and Zn-doped CdSe QDs show blue-shift with respect to their bulk counterpart as a result of quantum confinement effect. The highest luminescence intensity was observed for CdSe QDs doped with 4% Zn by PL studies. TEM analysis shows that the prepared QDs are spherical in shape.

    • Chemical nature of catalysts of oxide nanoparticles in environment prevailing during growth of carbon nanostructures by CCVD

      M JANA A SIL S RAY

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      Carbon nanostructures (CNS) are often grown using oxide nanoparticles as catalyst in chemical vapour deposition and these oxides are not expected to survive as such during growth. In the present study, the catalysts of cobalt- and nickel oxide-based nanoparticles of sizes varying over a range have been reduced at 575$^{\circ}$C under environment resulting from the introduction of C$_2$H$_2$ $+$ NH$_3$ during growth of CNS as well as under introductionof C$_2$H$_2$ and NH$_3$ separately. The structure of the reduced nanoparticles is often different from the equilibrium structure of the bulk. Nanoparticles of cobalt oxide with and without doping by copper oxide are reduced to cobalt alloy or cobalt nanoparticles having fcc structure, but the rate of reduction is relatively less in NH$_3$ environment. However, reduced nickel oxide nanoparticles with and without doping shows a mix of fcc and hcp phases. The presence of hydrogen and nitrogen in the environment appears to discourage the formation of hcp nickel as inferred from the results in NH$_3$ environment. Cobalt carbide forms when the 10 wt.% or less doped cobalt oxide is reduced in C$_2$H$_2$ $+$ NH$_3$ environment. At higher level of doping of 20 wt.%, separate metallic phase of copper appears andcarbide formation gets suppressed.

    • Fabrication and physical characteristics of new glasses from wastes of limestone and phosphorite rocks

      YASSER B SADDEEK K A ALY RABIE S FARAG M A M UOSIF K H S SHAABAN

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      In this work, new glasses were synthesized from wastes of limestone and phosphate rocks besides commercial borax. The glasses were characterized by FTIR, DTA, ultrasonic techniques and UV spectroscopy. It was found that the concentration of both CaO and P$_2$O$_5$ increases and the concentrations of B$_2$O$_3$ and Na$_2$O decrease as the content of phosphate rocks increases. Variation of the contents of the different oxides affects the concentration of the structural units constituting the glass, which was indicated by the behaviour of the fraction N$_4$ of BO$_4$ units in the borate matrix. The density and the refractive index of the glasses decrease as the CaO and P$_2$O$_5$ contents increase, which was attributed to the increase of [BO$_3$] structural units. On the other hand, the physical parameterssuch as the ultrasonic velocity, the elastic moduli, the optical bandgap and the optical polarizability increased, which was attributed to the higher coordination number of CaO$_6$ compared with the coordination of borate structuralunits and to the former effect of P$_2$O$_5$. As a result, a polymerization of the total co-ordination number of the glass, crosslink density and connectivity within the glass network will occur.

    • Structural, dielectric and a.c. conductivity study of Sb$_2$O$_3$ thin film obtained by thermal oxidation of Sb$_2$S$_3$

      M HAJ LAKHDAR T LARBI B KHALFALLAH B OUNI M AMLOUK

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      This work highlights some physical properties of Sb$_2$O$_3$ thin films obtained through heat treatment of Sb$_2$S$_3$ thin films under an atmospheric pressure at 400$^{\circ}$C. The obtained material is characterized by X-ray diffraction and impedance spectroscopy. X-ray diffraction analysis shows that Sb$_2$O$_3$ thin films were crystallized in cubic structure having a preferential growth along (222) plane. The grain size is found to be around 65 nm. The electrical conductivity was studied using impedance spectroscopy technique in the frequency range from 5 Hz to 13 MHz at temperatures lying in 638–698 K domain. Besides, the frequency and temperature dependence of the complex impedance, a.c. conductivity and complex electric modulus have been investigated.

    • Radiation modification of the properties of polypropylene/carboxymethyl cellulose blends and their biodegradability

      A M ABDEL GHAFFAR H E ALI

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      Polypropylene (PP)/carboxymethyl cellulose (CMC) blend films were prepared by changing content of CMC in the range of 0–20 wt%. Different analytical techniques such as thermogravimetric analysis (TGA), mechanicaltest and scanning electron microscopy (SEM) were used to investigate some selected properties such as thermal properties, tensile strength, elongation and morphology. Fourier transform infrared spectroscopy (FTIR) was performedto identify the chemical structure of the prepared blend films. The blend film with composition PP/15wt% CMC was selected due to its modified properties rather than other blends. The properties of original and irradiated PP/15wt% CMC blend were investigated. It was found that the swelling behaviour is slightly increased with increasing CMC content and does not exceed 7%. It is observed that for PP/15wt% CMC as irradiation dose increases the mechanical property (tensile strength) is enhanced up to 10 kGy and water resistant increases. The prepared PP/CMC with different concentration blends and the selected irradiated PP/15wt% CMC blend with different doses 0, 5, 10 and 20 kGy were subjected to biodegradation in soil burial tests for 6 months using two different types of soils,namely, agricultural and desert soils. The properties of original PP/CMC blends and irradiated PP/15wt% CMC blend that undergo biodegradation were investigated by mechanical test and SEM. From the study it can be concludedthat there is a possibility of using PP/15wt% CMC blend film irradiated to 10 kGy as a potential candidate for packaging purpose.

    • Linear and non-linear optical properties of amorphous Se and M5Se95 (M $=$ Ge, Ga and Zn) films

      GH ABBADY K A ALY Y SADDEEK N AFIFIY

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      The variations in structure and optical properties of amorphous a-Se and a-M$_5$Se$_{95}$ (M = Ge, Ga and Zn) films have been studied based on FTIR and optical measurements. FTIR transmittance spectra for a-Se and a-M$_5$Se$_{95}$ (M $=$ Ge, Ga and Zn) glasses were measured as a function of wavenumber. The addition of Ge, Ga and Zn increases the vibrational frequency of the a-Se main band. The absorption edge of Ge$_5$Se$_{95}$ shifted towards long side of the wavelength in comparison with that of a-Se film. This shift increases gradually in the case of Ga$_5$Se$_{95}$ and Zn$_5$Se$_95$ films. So, the optical bandgap ofM5Se95 films was decreased, but the index of refraction was increased. The first and third order of electric susceptibility ($\chi_{(1)}$ and $\chi_{(3)}$) and non-linear index of refraction ($n_2$) were increased by adding Ge, Ga and Zn into a-Se.

    • Microstructure and wear behaviour of FeAl-based composites containing in-situ carbides

      RAVI KANT UJJWAL PRAKASH VIJAYA AGARWALA V V SATYA PRASAD

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      Iron aluminides containing carbon are promising materials for tribological applications. Because of graphite formation at higher ($>$20 wt%) Al-contents the addition of carbon to FeAl-based alloys has not been successful.The graphite precipitation may be avoided by addition of Zr or Ti. Dry sliding wear behaviour of FeAl based alloys containing 1–1.5wt% carbon with quaternary addition of Ti or Zr has been studied using ball-on-disk wear test. Effect of sliding speeds and applied loads is investigated and correlated with mechanical properties. Wear resistance of FeAl-based alloys is found to be significantly improved on addition of Ti/Zr. This is attributed to the high hardness of alloy carbides. The lower load-bearing capacity of graphite flakes in localized region was found to increase the wear rate of the alloy. The carbides such as Fe$_3$AlC$_{0.5}$, TiC and ZrC are embedded in the matrix after sliding wear without destruction or delamination. This significantly affects the wear resistance of FeAl-based alloys.

    • Theoretical study of built-in-polarization effect on relaxation time and mean free path of phonons in Al$_x$Ga$_{1−x}$N alloy

      B K SAHOO A PANSARI

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      In this article we have investigated theoretically the effect of built-in-polarization field on various phonon scattering mechanisms in AlxGa1−xN alloy. The built-in-polarization field of AlxGa1−xN modifies the elastic constant,group velocity of phonons and Debye temperature. As a result, various phonon scattering mechanisms are changed. Important phonon scattering mechanisms such as normal scattering, Umklapp scattering, point defect scattering, dislocation scattering and phonon–electron scattering processes have been considered in the computation. The combined relaxation time due to above-mentioned scattering mechanisms has also been computed as afunction of phonon frequency for various Al compositions at room temperature. It is found that combined relaxation time is enhanced due to built-in-polarization effect and makes phonon mean free path longer, which is required forhigher optical, electrical and thermal transport processes. The result can be used to determine the effect of built-inpolarization field on optical and thermal properties of Al$_x$Ga$_{1−x}$N and will be useful, particularly, for improvementof thermoelectric performance of Al$_x$Ga$_{1−x}$N alloy through polarization engineering.

    • Physicochemical, structural and induced ferromagnetic properties of Co–In-codoped CdO synthesised via Cd chloride: significant effect of post-treatment hydrogen

      A A DAKHEL W E ALNASER

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      Nanoparticle solid solution powders of cadmium oxide doped with different concentrations of cobalt and indium ions were synthesised by solvothermal method through CdCl$_2$·H$_2$O precursor route. The objective of the present work is to study and develop conditions necessary to create stable room-temperature ferromagnets (RTFMs) in transparent conducting oxide (TCO) CdO for applications in the field of dilute magnetic semiconductors (DMSs). To achieve this aim, cobalt (Co$^{2+}$) dopant ions were used as a source of stable FM, while In$^{3+}$ dopant ions supply free electrons that enhance the electronic medium of interaction. The electronic medium in the host CdO lattice,which carries the long-range spin–spin ($S.S$) exchange interaction between localised Co$^{2+}$ (3d) spins of dopant ions, was further developed by annealing in hydrogen gas (hydrogenation). The crystalline structure of the powder samples was investigated by the X-ray diffraction (XRD) method. The optical absorption properties were studied by diffuse reflection spectroscopy (DRS). Magnetic measurements reveal that the Co–In-codoped CdO powder has FM properties superimposed on paramagnetic (PM) behaviour. However, annealing in hydrogen atmosphere strongly boosts the created FMso that the saturation magnetisation increases $\sim$90 times. Physical explanations and discussion are given in the article. Thus, it is proved that the magnetic properties could be tailored to TCO CdO by Co-doping and post-treatment under H$_2$ atmosphere.

    • X-ray structure, hydrogen bonding and lattice energy analysis of (2$E$)-1-(anthracen-9-yl)-3-(4-substitutedphenyl)prop-2-en-1-ones

      VINUTHA V SALIAN B NARAYANA K BYRAPPA B K SAROJINI RAJNI KANT

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      (2$E$)-1-(anthracen-9-yl)-3-(4-chlorophenyl)prop-2-en-1-ones and (2$E$)-1-(anthracen-9-yl)-3-(4-nitrophenyl) prop-2-en-1-ones crystallize in the monoclinic crystal system with space group P2$_1$/c. Single-crystal X-ray diffraction data for both the compounds were collected on an X’Calibur CCD area detector diffractometer (Oxford Diffraction)using Mo$K\alpha$ radiation ($\lambda = 0.7107$ $\AA$) at 293(2) K. The crystal structures were solved by direct methods and refined by full-matrix least-square procedures to a final $R$ value of 0.0468 [I] and 0.0486 [II]. The crystal structures as elucidated by X-ray diffraction methods show the presence of a few intermolecular interactions, and the nature and energetics associated with these interactions have been characterized using PIXEL software.

    • First-principle studies of the ternary palladates CaPd$_3$O$_4$ and SrPd$_3$O$_4$

      AMIN KHAN ZAHID ALI IMAD KHAN SAEID JALALI ASADABADI IFTIKHAR AHMAD

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      Ternary palladates CaPd$_3$O$_4$ and SrPd$_3$O$_4$ have been studied theoretically using density functional theory approach. The calculated structural properties are consistent with the experimental findings. Mechanical properties show that these compounds are elastically stable, anisotropic and ductile in nature. The electronic properties reveal that they are narrow band gap semiconductors with band gaps 0.12 and 0.10 eV, correspondingly. Both materials are optically active in the infrared ranges of the electromagnetic spectrum. Narrow band gap semiconductors are efficient thermoelectric (TE) materials; therefore, TE properties are also studied and discussed. Furthermore,DFT and post-DFT calculations confirm the paramagnetic nature of these compounds.

    • Loss of outer membrane integrity in Gram-negative bacteria by silver nanoparticles loaded with Camellia sinensis leaf phytochemicals: plausible mechanism of bacterial cell disintegration

      M SINGH A K MALLICK M BANERJEE R KUMAR

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      New generation antimicrobial and smart drugs are the needs of the present era in fighting microbial infection and various chronic diseases. Nowadays nanoparticles (NPs) are widely applied in biomedical fields by virtue of their surface modification, which enhances both target selectivity and function. This study is a continuation of our earlier study that demonstrated antimicrobial property of NPs against both Gram-positive and Gramnegative organisms (Goswami et al, 2015). Silver NPs were synthesized using tea leaves (Camellia sinensis) decoction and were characterized using UV-vis spectrophotometry, transmission electron microscopy (TEM) and Fouriertransformed infrared spectroscopy (FTIR). The silver NPs were stable at various environmental conditions. The stability of the particles may be due to various phytochemicals of tea that were bound to the surface of reducedsilver ions as a capping agent. The antimicrobial activity of NP was investigated against three Gram-negative pathogenic bacteria (Shigella dysentriae, Salmonella infestis and Vibrio parahaemolyticus). The outer membrane ofGram-negative bacteria is a lipopolysaccharide (LPS) in nature and provides protection from various stress conditions and antibiotics. But a silver NP destroys its membrane integrity and thus helps in cell killing. Spectral changesconfirmed NP interaction with hydrophobic moiety of LPS. Minimum inhibitory concentrations for S. dysentriae, S. infestis and V. parahaemolyticus were 3.75, 5.25 and 5.25 $\mu$g ml$^{−1}$, respectively. Inhibition of biofilm formationwas significant with the three bacterial strains. Cytoplasmic leakage from each bacterial strain was also demonstrated on account of NP treatment. The particles demonstrated good biocompatibility. No damage of human buccal mucosal cells was recorded even at concentration of 10 mg ml$^{−1}$. Thus, silver NPs would be potential oral therapeutic molecules against Gram-negative bacteria.

    • Volume Contents

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