Nikola Cvjetićanin

Synthesis and characterization of CdS quantum dots–polystyrene composite

Methodology for incorporation of 50 A CdS quantum dots (QD) in a polystyrene matrix, based on phase transfer of CdS quantum dots from an aqueous to organic phase, was developed. The obtained composite was characterized using optical, structural and thermal techniques. Infra red measurements revealed formation of chemical bonds between the surface of the CdS QDs and the polystyrene matrix. The polystyrene matrix blocked the surface states that promote radiationless recombination, resulting in enhanced band-to-band luminescence of CdS QDs. On the other hand, in the presence of CdS QDs the thermal decomposition of polystyrene was shifted towards higher temperature for about 100∞C. ” 2000 Elsevier Science B.V. All rights reserved.

Conductivity, viscosity and IR spectra of Li, Na and Mg perchlorate solutions in propylene carbonate/water mixed solvents

The influence of water addition on the electric conductivity, viscosity and IR spectra of Mg, Li and Na perchlorate solutions in propylene carbonate (PC) was examined. Conductivity and viscosity data pointed out ion–solvent and ion–ion associations that were most pronounced in Mg(ClO4)2 solutions. IR investigations were directed towards the spectral region 1000–600 cm-1. The changes of the ν4 band of the perchlorate anion at 624 cm-1 and the changes of solvent bands in the spectral region 980–890 cm-1 caused by water addition to 1 M solutions indicated the formation of contact ion pairs. The appearance and increase in intensity of the otherwise IR-inactive perchlorate band at 931 cm-1, upon water addition, was attributed to cation–H2O–ClO4- solvent shared ion pairs.

Structural and Dielectric Properties of BaTi1-xSnxO3 Ceramics

BaTi1-xSnxO3 (BTS) powders, with x ranging from 0 to 1, were synthesized by solid-state reaction technique. The powders were pressed into pellets and sintered at 1370 and 1420 oC. The structural characterization of sintered BTS samples was made at room temperature using X-ray diffraction and Raman spectroscopy measurements. The BTS samples were found to be singlephase solid solutions. Dielectric properties of sintered BTS samples were studied as a function of sintering temperatures and tin contents, too. For samples with x ranging from 0 up to 0.15, it has been found that the Curie temperature decreases while the maximum of the dielectric constant increases with increasing tin content. These samples have relatively high dielectric constants, contrary to x > 0.2 samples with very low dielectric constants. It is noticed that BTS ceramics sintered at 1420 oC exhibit better dielectric properties than those sintered at 1370 oC.

Electric conductivity of Na and Ag forms of A and X zeolites. The effect of cluster formation on the conductivity

Abstract The electric conductivity of Na and Ag forms of zeolites in the temperature range from room temperature to 500°C was measured by the ac impedance method. The Ag forms of zeolites exhibit a lower electric conductivity than the corresponding Na forms, which is ascribed to the formation of Ag n q + clusters in the process of dehydration. The clusters can be partly oxidized by oxygen and that is manifested in an increase of electric conductivity.

Electrochemical Synthesis and Structure of Poly(2‐methyl‐1‐naphthylamine) Films

A novel polymer, poly(2‐methyl‐1‐naphthylamine), which was synthesized electrochemically at various temperatures from a solution containing 2‐methyl‐1‐naphthylamine, acetic acid and sodium acetate, was characterized by IR spectroscopy. The structural conclusions were based on comparisons of polymer spectra with the IR‐spectrum of the monomer, 2‐methyl‐1‐naphthylamine. IR spectroscopy indicates that the electropolymerization proceeds via the –NH2 groups and that the poly(2‐methyl‐1‐naphthylamine) structure consists of imine (–N˭C) and amine (–NH–C) links between naphthalene rings as well as a free methyl groups in the chains. An analysis of the “substitution pattern” region in the polymers spectra suggests that the polymer molecules were formed via mixed N–C(4), N–C(5) and N–C(7) linkages between repeated units. The ratio of between the 1645 and 1620 cm− 1 peak areas decreases with increased temperature during synthesis, indicating that 25°C is the best temperature to obtain higher molecular weights.

A study on the kinetics and mechanism of silver-cluster formation in zeolite Ag-X by diffuse reflectance spectroscopy

Abstract The kinetics of silver-cluster formation was investigated using diffuse reflectance spectroscopy (DRS), by following the intensity changes of the absorption band at 410 nm that appears under the thermal dehydration of zeolite Ag-X. Using the theoretical model of diffusion into a sphere, it was shown that the diffusion of Ag + is the rate determining step in the silver-cluster formation. This model also enabled the calculation of some kinetic parameters.

Comparison between Different LiFePO4 Synthesis Routes

Olivine-type lithium iron phosphate (LiFePO4) powders were synthesized applying three different methods: solid state reaction at high temperature, ultrasonic spray pyrolysis, and sonochemical treatment. The samples were characterized by X-ray powder diffraction (XRPD). Particle morphologies of the obtained powders were determined by scanning electron microscopy (SEM). It was found that structural and microstructural parameters of this material were strongly dependent on the synthesis conditions. We present here the results obtained upon optimization of each procedure for designing this cathode material.

Properties of LiMn2O4 Powders Obtained by Ultrasonic Spray Pyrolysis

LiMn2O4 powders were synthesized by ultrasonic spray pyrolysis. By varying the cooling conditions, two samples of powders were obtained: quenched in water (Q) and spontaneously cooled to room temperature (SC). The crystal structure of the as-prepared powders was revealed by X-ray powder diffraction. Structure refinements confirm that SC sample crystallizes in Fd3m space group, while Q sample crystallizes in I4l/amd space group. Particle morphology was determined by scanning electron microscopy. Electrochemical intercalation and deintercalation were examined in galvanostatic regime.

Raman spectroscopic study of lithium and sodium perchlorate association in propylene carbonate-water mixed solvents

Raman spectra of 1 M solutions of LiClO4 and NaClO4 in propylene carbonate (PC) with different amounts of water added (H2O/cation mole ratio = 0–55.5) were recorded in the spectral region 880–980 cm−1. Principal component analysis, a statistical method and deconvolution were applied in investigating the association in these solutions. The results indicate the existence of a band at the high-wavenumber side of the ν1 band of free perchlorate anion. As established by deconvolution, the position of the band is at 938–940 cm−1. This band is attributed to monodentate contact ion pairs and is present in the solutions of perchlorates in pure PC and with a minimum amount of water added. The presence of monodentate contact ion pairs was established by deconvolution of the Raman spectrum of a 1 M solution of Mg(ClO4)2 in pure PC, but at very low concentration. Copyright

Screen Printed BaTi1-xSnxO3 Multilayer Materials

BaTi1-xSnxO3 (BTS) piezoceramics with multilayer structure were prepared. The Sn concentration in the layers was changed from x=0.025 to 0.15. Thick films were screen-printed on alumina substrates electroded with Ag/Pd. The BTS piezoceramics were sintered at 850C for 10 minutes. The thickness was 45-150 μm depending on the number of layers. The microstructure of piezoceramic materials and the compatibility of BTS layers with substrates were investigated by SEM and EDX. The dielectric properties were measured and the results reported.