Synthesis, structural and optical properties of nanocrystalline Ba2NaNb5O15

Fine powders comprising nanocrystallites of barium sodium niobate, Ba2NaNb5O15 (BNN) were obtained via a citrate assisted sol-gel route at a much lower temperature than that of the conventional solid-state reaction route. The phase evolution of BNN as a function of temperature was investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). DTA data followed by XRD studies confirmed the BNN formation temperature to be around 923 K. The as-synthesized powders heat-treated at 923 K/10 h attained an orthorhombic structure akin to that of the parent BNN phase. Transmission electron microscopy revealed that the nanocrystallites are associated with dislocations. The optical band gap was calculated using the Kubelka-Munk function. These nanocrystallites exhibited strong visible photoluminescence (PL) at room temperature. The PL mechanism was explained by invoking the dielectric confinement effect, defect states and generation of self-trapped excitons.

Effect of low oxygen pressure on structural and magnetic properties of quenched SrFe12O19 thin films

Strontium hexaferrite thin films have been grown on glass substrates at room temperature in oxygen environment by pulsed laser deposition method. The effect of oxygen pressure (p(o2)) on the structural and magnetic properties has been investigated. The as-deposited films were found to be amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 850 A degrees C in air. The thickness of the film increased with p(o2). The film grown at p(o2) = 0.455 Pa had a clear hexagonal structure. The values of coercivity for the films were found to increase with p(o2).

Hydrothermal synthesis of Gd2O3:Eu3+ nanophosphors: Effect of surfactant on structural and luminescence properties

Various morphologies of Eu3+ activated gadolinium oxide have been prepared by hydrothermal method using hexadecylamine (HDA) as surfactant at different experimental conditions. The powder X-ray diffraction studies reveal as-formed product is hexagonal Gd(OH)(3):Eu3+ phase and subsequent heat treatment at 350 and 600 degrees C transforms to monoclinic GdOOH:Eu3+ and cubic Gd2O3:Eu3+ phases respectively. SEM pictures of without surfactant show irregular shaped rods along with flakes. However, in the presence of HDA surfactant, the particles are converted into rods of various sizes. The temperature dependent morphological evolution of Gd2O3:Eu3+ without and with HDA surfactant is studied. TEM micrographs of Gd(OH)(3):Eu3+ sample with HDA confirms smooth nanorods with various diameters in the range 20-100 nm. FTIR studies reveal that HDA surfactant plays an important role in conversion of cubic to hexagonal phases. Among these three phases, cubic phase Gd2O3:Eu3+ (lambda(ex) = 254 nm) show red emission at 612 nm corresponding to D-5(0)-> F-7(2) and is more efficient host than the monoclinic counterpart. The band gap for hexagonal Gd(OH)(3):Eu3+ is more when compared to monoclinic GdOOH:Eu3+ and cubic Gd2O3:Eu3+. (C) 2013 Elsevier B. V. All rights reserved.

Pulsed Electrical Stimulation and Surface Charge Induced Cell Growth on Multistage Spark Plasma Sintered Hydroxyapatite-Barium Titanate Piezobiocomposite

The primary purpose of the present work was to illustrate whether cell proliferation can be enhanced on electroactive bioceramic composite, when the cells are cultured in the presence of external electrical stimulation. The two different aspects of the influence of electric field (E-field) application toward stimulating the growth/proliferation of bone/connective tissue cells in vitro, (a) intermittent delivery of extremely low strength pulsed electrical stimulation (0.5-4V/cm, 400s DC pulse) and (b) surface charge generated by electrical poling (10kV/cm) of hydroxyapatite (HA)-BaTiO3 piezobiocomposite have been demonstrated. The experimental results establish that the cell growth can be enhanced using the new culture protocol of the intermittent delivery of electrical pulses within a narrow range of stimulation parameters. The optimal E-field strength for enhanced cellular response for mouse fibroblast L929 and osteogenic cells is in the range of 0.5-1V/cm. The MTT 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide] assay results suggested the increased viability of E-field treated cells over 7d in culture, implicating the positive impact of electrical pulses on proliferation behavior. The alizarin red assay results showed noticeable increase in Ca-deposition on the E-field treated samples in comparison to their untreated counterparts. The negatively charged surfaces of developed piezocomposite stimulated the cell growth in a statistically noticeable manner as compared with the uncharged or positively charged surfaces of similar composition.

Synthesis, structural and thermoluminescence properties of YAlO3:Dy3+ nanophosphors

Thermoluminescence properties of YAlO3:Dy3+ nanophosphor prepared by a low temperature solution combustion (SC) method using oxalyl dihydrazide as a fuel were studied and the results were compared to bulk phosphor prepared by solid state (SS) synthesis. Powder X-ray diffraction patterns confirm the orthorhombic phase of SC and SS methods. Rietveld refinement was used to estimate the cell parameters of undoped and Dy3+ doped YAlO3. Scanning electron micrographs reveal dumbbell shape particles. Electron paramagnetic resonance spectra of YAlO3:Dy3+ nanophosphors were studied at 293 K, 77 K and 10 K. Thermoluminescence responses of SC and SS prepared phosphor were studied using gamma irradiation in the dose range 0.1-6 kGy at a warming rate of 1 degrees C s (1) at room temperature (RT). The optimized concentrations of Dy3+ ions in YAlO3 was found to be 3 mol%. The trapping parameters (i. e. activation energy, frequency factor, order of kinetic) of all the individual peaks of the glow curves have been analysed by using Chen's method. The low fading and linear response in the wide range (0.1-1 kGy) suggests the possibility of usage of SC prepared phosphor in dosimeter applications. (C) 2013 Elsevier B. V. All rights reserved.

A structural and spectroscopic investigation of reduced graphene oxide under high pressure

The effect of high pressure on reduced graphene oxide (RGO) has been investigated using X-ray diffraction (XRD) and infrared (IR) absorption spectroscopy. Our XRD measurements show two-step reversible compression in the inter-layer spacing of RGO whereas intra-layer ordering exhibits a high pressure behavior similar to that of graphite up to 20 GPa. The line shape analysis of (100) peak, representing the intra-layer ordering, suggests presence of local out of plane distortions in RGO in the form of puckered regions which progressively straighten out as a function of pressure. IR measurements show reversible changes in spectroscopic features attributed to remnant functional groups in the inter-layer region. These measurements suggest high stability and recovering ability of RGO under pressure cycling. (C) 2014 Elsevier Ltd. All rights reserved.

Low temperature synthesis of pure cubic ZrO2 nanopowder: Structural and luminescence studies

Pure cubic zirconia (ZrO2) nanopowder is prepared for the first time by simple low temperature solution combustion method without calcination. The product is characterized by Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infra Red spectroscopy (FTIR) and Ultraviolet-Visible spectroscopy (UV-Vis). The PXRD showed the formation of pure stable cubic ZrO2 nanopowders with average crystallite size ranging from 6 to 12 nm. The lattice parameters were calculated from Rietveld refinement method. SEM micrograph shows fluffy, mesoporous, agglomerated particles with large number of voids. TEM micrograph shows honey comb like arrangement of particles with particle size similar to 10 nm. The PL emission spectrum excited at 210 nm and 240 nm consists of intense bands centered at similar to 365 and similar to 390 nm. Both the samples show shoulder peak at 420 nm, along with four weak emission bands at similar to 484, similar to 528, similar to 614 and similar to 726 nm. TL studies were carried out pre-irradiating samples with gamma-rays ranging from 1 to 5 KGy at room temperature. A well resolved glow peak at 377 degrees C is recorded which can be ascribed to deep traps. With increase in gamma radiation there is linear increase in TL intensity which shows the possible use of ZrO2 as dosimetric material. (C) 2013 Elsevier B.V. All rights reserved.

Effect of pH on structural and magnetic properties of nanocrystalline Y3Fe5O12 by aqueous co-precipitation method

The Y3Fe5O12 (YIG) nanopowders were synthesised at different pH using co-precipitation method. The effect of pH on the phase formation of YIG is characterised using XRD, TEM, FTIR and TG/DTA. From the Scherer formula, the particle sizes of the powders were found to be 13, 19 and 28 nm for pH=10, 11 and 12 respectively. It is found that as the pH of the solution increase the particle size is also increases. It is also clear from the TG/DTA curves that as the pH is increasing the weight losses were found to be small. The nanopowders were sintered at 600, 700, 800 and 900 degrees C for 5 h using conventional sintering method. The phase formation is completed at 800 degrees C/5 h which is correlated with TG/DTA. The average grain size of the samples is found to be similar to 161 nm. The high values of M-s=23 emu g(-1) and H-c=22 Oe were recorded for the sample sintered at 900 degrees C.

Structural and kinetic studies on adenylosuccinate lyase from Mycobacterium smegmatis and Mycobacterium tuberculosis provide new insights on the catalytic residues of the enzyme

Adenylosuccinate lyase (ASL), an enzyme involved in purine biosynthesis, has been recognized as a drug target against microbial infections. In the present study, ASL from Mycobacteriumsmegmatis (MsASL) and Mycobacteriumtuberculosis (MtbASL) were cloned, purified and crystallized. The X-ray crystal structure of MsASL was determined at a resolution of 2.16 angstrom. It is the first report of an apo-ASL structure with a partially ordered active site C3 loop. Diffracting crystals of MtbASL could not be obtained and a model for its structure was derived using MsASL as a template. These structures suggest that His149 and either Lys285 or Ser279 of MsASL are the residues most likely to function as the catalytic acid and base, respectively. Most of the active site residues were found to be conserved, with the exception of Ser148 and Gly319 of MsASL. Ser148 is structurally equivalent to a threonine in most other ASLs. Gly319 is replaced by an arginine residue in most ASLs. The two enzymes were catalytically much less active compared to ASLs from other organisms. Arg319Gly substitution and reduced flexibility of the C3 loop might account for the low catalytic activity of mycobacterial ASLs. The low activity is consistent with the slow growth rate of Mycobacteria and their high GC containing genomes, as well as their dependence on other salvage pathways for the supply of purine nucleotides. Structured digital abstract andby()

Structural and thermodynamic properties of Fe1.12Te with multiple phase transitions

The parent compound of iron chalcogenide superconductors, Fe1+yTe, with a range of excess Fe concentrations exhibits intriguing structural and magnetic properties. Here, the interplay of magnetic and structural properties of Fe1.12Te single crystals have been probed by low-temperature synchrotron X-ray powder diffraction, magnetization, and specific heat measurements. Thermodynamic measurements reveal two distinct phase transitions, considered unique to samples possessing excess Fe content in the range of 0.11 <= y <= 0.13. On cooling, an antiferromagnetic transition, T-N approximate to 57K is observed. A closer examination of powder diffraction data suggests that the transition at TN is not purely magnetic, but accompanied by the commencement of a structural phase transition from tetragonal to orthorhombic symmetry. This is followed by a second prominent first-order structural transition at T-S with T-S < T-N, where an onset of monoclinic distortion is observed. The results point to a strong magneto-structural coupling in this material. (C) 2014 AIP Publishing LLC.

Density Functional Theoretical Modeling, Electrostatic Surface Potential and Surface Enhanced Raman Spectroscopic Studies on Biosynthesized Silver Nanoparticles: Observation of 400 pM Sensitivity to Explosives

Interaction of adsorbate on charged surfaces, orientation of the analyte on the surface, and surface enhancement aspects have been studied. These aspects have been explored in details to explain the surface-enhanced Raman spectroscopic (SERS) spectra of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW or CL-20), a well-known explosive, and 2,4,6-trinitrotoluene (TNT) using one-pot synthesis of silver nanoparticles via biosynthetic route using natural precursor extracts of clove and pepper. The biosynthesized silver nanoparticles (bio Ag Nps) have been characterized using UV-vis spectroscopy, scanning electron microscopy and atomic force microscopy. SERS studies conducted using bio Ag Nps on different water insoluble analytes, such as CL-20 and TNT, lead to SERS signals at concentration levels of 400 pM. The experimental findings have been corroborated with density functional computational results, electrostatic surface potential calculations, Fukui functions and potential measurements.

Gd1.96-xYxEu0.04O3 (x=0.0, 0.49, 0.98, 1.47, 1.96 mol%) nanophosphors: Propellant combustion synthesis, structural and luminescence studies

Gd1.96-xYxEu0.04O3 (x = 0.0, 0.49, 0.98, 1.47, 1.96 mol%) nanophosphors were synthesized by propellant combustion method at low temperature (400 degrees C). The powder X-ray diffraction patterns of as formed Gd1.96Eu0.04O3 showed monoclinic phase, however with the addition of yttria it transforms from monoclinic to pure cubic phase. The porous nature increases with increase of yttria content. The particle size was estimated from Scherrer's and W-H plots which was found to be in the range 30-40 nm. These results were in well agreement with transmission electron microscopy studies. The optical band gap energies estimated were found to be in the range 5.32-5.49 eV. PL emission was recorded under 305 nm excitation show an intense emission peak at 611 nm along with other emission peaks at 582, 641 nm. These emission peaks were attributed to the transition of D-5(0) —> F-7(J) (J = 0, 1, 2, 3) of Eu3+ ions. It was observed that PL intensity increases with increase of Y content up to x = 0.98 and thereafter intensity decreases. CIE color co-ordinates indicates that at x = 1.47 an intense red bright color can be achieved, which could find a promising application in flat panel displays. The cubic and monoclinic phases show different thermoluminescence glow peak values measured under identical conditions. The response of the cubic phase to the applied dose showed good linearity, negligible fading, and simple glow curve structure than monoclinic phase indicating that suitability of this phosphor in dosimetric applications. (C) 2014 Elsevier B.V. All rights reserved.

Comparison of structural and luminescence properties of Dy2O3 nanopowders synthesized by co-precipitation and green combustion routes

Dysprosium oxide (Dy2O3) nanopowders were prepared by co-precipitation (CP) and eco-friendly green combustion (GC) routes. SEM micrographs prepared by CP route show smooth rods with various lengths and diameters while, GC route show porous, agglomerated particles. The results were further confirmed by TEM. Thermoluminescence (TL) responses of the nanopowder prepared by both the routes were studied using gamma-rays. A well resolved glow peak at 353 degrees C along with less intense peak at 183 degrees C was observed in GC route while, in CP a single glow peak at 364 degrees C was observed. The kinetic parameters were estimated using Chen's glow peak route. Photoluminescence (PL) of Dy2O3 shows peaks at 481, 577,666 and 756 nm which were attributed to Dy3+ transitions of F-4(9/2)-H-6(15/2), H-6(11/2), H-6(11/2) and H-6(9/2), respectively. Color co-ordinate values were located in the white region as a result the product may be useful for the fabrication of WLED'S. (C) 2014 Elsevier Ltd. All rights reserved.

Eco-friendly green synthesis, structural and photoluminescent studies of CeO2:Eu3+ nanophosphors using E. tirucalli plant latex

The investigation involves preparation and photoluminescence properties of CeO2:Eu3+ (1-11 mol%) nano phosphors by eco-friendly green combustion route using Euphorbia tirucalli plant latex as fuel. The final product was characterized by powder X-ray diffraction (PXRD), Scanning electron microcopy (SEM) and Transmission electron microscopy (TEM). The PXRD and SEM results reveals cubic fluorite phase with flaky structure. The crystallite size obtained from TEM was found to be similar to 20-25 nm, which was comparable to W-H plots and Scherrer's method. Photoluminescence (PL) emission of all the Eu3+ doped samples shows characteristic bands arising from the transitions of D-5(0) -> F-5(J) (J = 0, 1, 2, 3, 4) manifolds under excitation at 373 and 467 nm excitation. The D-5(0) -> F-7(2) (613 nm) transition often dominate the emission spectra, indicating that the Eu3+ cations occupy a site without inversion center. The highest PL intensity was recorded for 9 mol% Eu3+ ions with 5 ml latex. PL quenching was observed upon further increase in Eu3+ concentration. The international commission on illumination (CIE) chromaticity co-ordinates were calculated from emission spectra, the values (x, y) were very close to national television system committee (NTSC) standard values of pure red emission. The results demonstrate that the synthesized phosphor material could be very useful for display applications. Further, the phosphor material prepared by this method was found to be non toxic, environmental friendly and could be a potential alternative to economical routes. (C) 2014 Elsevier B.V. All rights reserved.

Effect of wettability and surface roughness on ice-adhesion strength of hydrophilic, hydrophobic and superhydrophobic surfaces

The anti-icing properties of hydrophilic, hydrophobic and superhydrophobic surfaces/coatings were evaluated using a custom-built apparatus based on zero-degree cone test method. The ice-adhesion reduction factor (ARF) of these coatings has been evaluated using bare aluminium alloy as a reference. The wettability of the surfaces was evaluated by measuring water contact angle (WCA) and sliding angle. It was found that the ice-adhesion strength (tau) on silicone based hydrophobic surfaces was similar to 43 times lower than compared to bare polished aluminium alloy indicating excellent anti-icing property of these coatings. Superhydrophobic coatings displayed poor anti-icing property in spite of their high water repellence. Field Emission Scanning Electron Microscope reveal that Silicone based hydrophobic coatings exhibited smooth surface whereas the superhydrophobic coatings had a rough surface consisting of microscale bumps and protrusions superimposed with nanospheres. Both surface roughness and surface energy play a major role on the ice-adhesion strength of the coatings. The 3D surface roughness profiles of the coatings also indicated the same trend of roughness. An attempt is made to correlate the observed ice-adhesion strength of different surfaces with their wettability and surface roughness. (C) 2014 Elsevier B.V. All rights reserved.