Synthesis of LiCrxMn2-xO4 (x~0.18) by glycine-nitrate method

LiCr0.18Mn1.82O4 spinel has been successfully synthesized by glycine-nitrate method. As a cathode material for lithium batteries it shows initial discharge capacity of 107.1 mAh/g and capacity retention of 93.3% after ten cycles.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

Phonon Investigations in YVO4: Eu3+ Nanopowders

In this work two methods of preparation of yttrium orthovanadate nanopowders were presented: Solid State Reaction (top – down approach) and Solution Combustion Synthesis (bottom – up approach). For starting structural characterization, X – Ray Powder Diffraction (XPRD) and Field Emission Scanning Electron Microscopy (FESEM) were used. We report the change in reflection spectra in europium doped YVO4 nanopowders with comparison to its bulk analog. In UV – Vis reflection spectra we consider the change in values of band gap in these structures, after resizing it from bulk to nanomaterial. In Far – Infrared (FIR) reflection spectra, we registered the existence of Surface Optical Phonon (SOP) and different multi – phonon processes which alter the reflection spectra of bulk YVO4 . The influence of Eu ions is reflected through multi – phonon processes that occur and are connected with energy transfer from YVO4 lattice to Eu ions. All IR spectra were modeled using classical oscillator model with Drude part added which takes into account the free carrier contribution. Since our samples are distinctively inhomogeneous materials, we use Effective Medium theory in Maxwell Garnett approximation to model its effective dieletric function.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad

The structure and electrochemical properties of fayalite Fe2SiO4

Fayalite has been found various applications in many fields. Here is presented its use as anode material for lithium ion batteries. The syntheses of Fe2SiO4 and its composite with carbon are conducted through solid-state reaction at 850 °C under inert atmosphere of argon, using cheap and abundant precursors (Fe(NO3)3×9H2O and amorphous silica). Citric acid served as carbon source. The phase-purity of synthesized powders is checked by X-ray powder diffraction. The crystal structure of the powders is refined in orthorhombic Pbnm space group. Half-cell configuration, with lithium metal as counter electrode and fayalite as working electrode, is used for electrochemical measurements: galvanostatic cycling and electrochemical impedance spectroscopy

Structural and electrochemical study of lithium iron (II) pyrophosphate

Lithium iron(II) pyrophosphate, Li2FeP2O7, attracts attention of researchers for application as a cathode material in rechargeable lithium batteries. Li2FeP2O7 has somewhat higher voltage than commercial LiFePO4 (3.5 and 3.4 V, respectively), thus enables higher energy density, and also provides the possibility of two-electron reaction during intercalation. Within this study, pristine Li2FeP2O7 and its composite with carbon Li2FeP2O7/C were synthesized, with the carbon being formed by the pyrolysis of organic precursor in situ during formation of Li2FeP2O7 at high temperature. The polymer of methylcellulose was used as carbon source because of its ability to reversibly, depending on temperature, dissolve or gel in water. The structural, electrical and electrochemical characteristics of prepared powders were investigated by means of X-ray diffraction analysis, Mossbauer spectroscopy, impedance spectroscopy and galvanostatic charge/discharge testing. The results imply that in situ formation of carbon alters lattice parameters, decreases crystallite size, and facilitates lithium ion intercalation/deintercalation processes. The Ministry of Education, Science and Technological Development of the Republic of Serbia provided financial support for this study under Grant No. III 4500

Experimental Studies of The Evaporation of Pure Liquid Droplets in A Single-Axis Non-Resonant Levitator

Though a simple daily observation, evaporation of drops is still poorly understood due to the complex nature that involves hydrodynamic effects in the bulk fluids and transport phenomena at the liquid-vapor interface. This paper reports on the evaporation of single component droplets (water, ethanol, acetone, and glycerol) levitated in a single-axis non-resonant levitator. It was observed that the acetone and ethanol evaporated faster than water, although the acetone is the most volatile. The estimated lifetime of acetone is less than 5min, which is much shorter as compared to 56min for ethanol or about 90min for water droplets. On the other hand, glycerol showed no tendency to evaporate. With increasing the evaporation time, the ratio of large and small semi-axis decreases and tends to 1 corresponding to changes in drops shape from oblate ellipsoid to a sphere. Based on the classical D2-law, the surface regression rates have been estimated. © 2020 All Rights Reserved

Radiolytic synthesis and characterization of PVA/Au nanocomposites: The influence of pH values

Nanocomposites which consist of polymer matrix and nanoparticles of noble metal are a very important class of nanomaterials. The optical properties of these materials are strongly dependent on the nanoparticles size as well as on the synthesized procedure of nanocomposites preparation. In this work the Au nanoparticles were synthesized by the simple radiolytic procedure, using steady state gamma irradiation, under different pH values. PVA/Au nanocomposite films were obtained by solvent evaporation from Au colloids. UV-Vis absorption spectra of Au colloids show absorption in the range of 450 to 650 nm with the maximum around 520 nm, which is the typical plasmon band of Au nanoparticles. Absorption spectra of PVA/Au nanocomposites are red shifted compared to corresponding primary Au colloids. This red shift is not result of any change in particle size distribution and can be explained by the change of dielectric property of surrounding medium. IR spectra indicated anchoring the OH groups of PVA molecule at the cluster surface. This effect limits the growing of the metal clusters and confirmed that the PVA is a god matrix for in situ synthesis of Au nanoparticles. The size of Au nanoparticles is dependent on the experimental conditions. Obtained results indicated that the pH value of solution played an important role. The values of absorption maximum were not dependent on the concentration of Au3+ cations, but show strong dependence on the pH value of the initial solution. The increase of pH value reduced the mean diameters of nanoparticles. The lowest value of lambda(max) was obtained for colloid with pH 7, which theoretically corresponds to the nanoparticles with minimum dimension. These results are in agreement with the XRD measurement of PVA/Au nanocomposite films and theoretical calculations. According to obtained results of radiolytic synthesis of Au nanoparticles in PVA solution can be conclude that it is possible to control the particle size by tuning the pH value of solution.6th Conference of Young Researchers, Dec 24-26, 2007, Belgrade, Serbi

Electrochemical Behaviour of V2O5 Xerogel and V2O5 Xerogel/C Composite in an Aqueous LiNO3 and Mg(NO3)(2) Solutions

We synthesized both the V2O5 xerogel and the composite V2O5 xerogel/C starting from the solution of V2O5 in hydrogen peroxide. After the characterization by XRD, thermal (TCA-DTA), SEM methods and by particle size analysis, the investigation of Li+ and Mg2+ intercalation/deintercalation reactions in an aqueous solutions of LiNO3 and Mg(NO3)(2) were performed by cyclic voltammetry. The composite material V2O5 xerogel/C displayed relatively high intercalation capacity, amounting to 123 mA h g(-1) and 107 mA h g(-1), in lithium and magnesium salt solutions, respectively.11th Annual Conference of the Materials-Research-Society-of-Serbia (YUCOMAT 2009), Aug 31-Sep 04, 2009, Herceg Novi, Montenegr

Compaction pressure's influence on density and electrical properties of sintered cordierite-based ceramics

Mechanical activation is widely used for sample preparation before the sintering process. However, the influence of pressure, which is used for compaction, has not been completely investigated. Cordierite, 2MgO_2Al2O3_5SiO2, is a very attractive high-temperature ceramic material, due to its outstanding electrical characteristics, such as the low temperature expansion coefficient, low dielectric constant and good mechanical properties. Based on our previous investigation, the mechanical activation of the starting mixtures with 5.00 mass% TiO2 was performed in a high energy ball mill during 10 minutes. Compaction pressure varied from 0.5 to 6 t/cm2. Differential thermal analysis (DTA) was used in order to determine characteristic temperatures within the system during heating. Sintering process was performed at 1350 °C for 4 h in air atmosphere. The phase composition of activated and sintered samples was analyzed by the X-ray diffraction method. Scanning electron microscopy was performed to analyze both compacted and sintered sample microstructure. This paper deals with the influence of compaction pressure on the densities of green bodies as well as on the sintered samples, along with electrical propertie

A study of defect structures in Fe-alloyed ZnO: Morphology, magnetism, and hyperfine interactions

In order to study the effect of Fe cation substitution on the local structure, defect formation, and hyperfine interactions in ZnO, Mössbauer spectroscopy measurements of the microwave processed Zn1−xFexO (x=0.05, 0.10, 0.15, and 0.20) nanoparticles, together with ab initio calculations, were performed. Complementary information on the distribution of particle size and morphology, as well as magnetic properties, were obtained by X-ray diffraction, transmission electron microscopy, and squid-magnetometry. The selected model for analyzing the Mössbauer spectra of our samples is a distribution of quadrupole splittings. The fitting model with two Lorentz doublets was rejected due to its failure to include larger doublets. The Fe3+ ions do not yield magnetic ordering in the samples at room temperature. The results from first-principles calculations confirm that the major component of the Mössbauer spectra corresponds to the Fe-alloyed ZnO with Zn vacancy in the next nearest neighbor environment. The magnetic measurements are consistent with the description of the distribution of iron ions over the randomly formed clusters in the ZnO host lattice. While at room temperature all the samples are paramagnetic, magnetic interactions cause a transition into a cluster spin-glass state at low temperatures

Influence of one activated component on the sintering process of three phase system

According to its low temperature thermal expansion coefficient, low dielectric constant, also good mechanical properties, cordierite, 2MgO×2Al2O3×5SiO2, represents a very attractive hightemperature ceramic material. In this study, cordierite was prepared by solid state reaction of the MgO, Al2O3 and SiO2 mixture. One of the components from the mixture, SiO2, was mechanically activated in a high energy ball mill during 5 and 10 minutes. The applied pressure before the sintering process was 2 t/cm2. Sintering process of mixtures containing non-activated and activated SiO2 powder was performed at 1350 oC for 4h in the air atmosphere. The phase composition of starting oxides and sintered samples was analyzed by the X-ray diffraction method. Particle size analysis was performed to investigate the differences between starting components. Scanning electron microscopy was done to analyze the microstructure of both components and sintered samples. This paper investigates the influence of one mechanically activated SiO2 component on the densities of green bodies as well as on the sintered samples, along with electrical properties of cordierite ceramics