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Preparation and Characterization of Nano Ferrites

100%
Lazarević Z., Jovalekić Č., Milutinović A., Romčević M., Romčević N.
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EN
Nickel ferrite (NiFe_2O_4) and manganese ferrite (MnFe_2O_4) have been prepared by a soft mechanochemical route from mixture of (1) Ni(OH)_2 and α-Fe_2O_3 and (2) Mn(OH)_2 and α-Fe_2O_3 powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the NiFe_2O_4 and MnFe_2O_4 spinel phases were followed by X-ray diffraction, Raman and infrared spectroscopy, scanning and transmission microscopy. The spinel phase formation was first observed after 4 h of milling (case 1) and after 3 h (case 2) and its formation was completed after 25 h in both cases. The synthesized NiFe_2O_4 and MnFe_2O_4 ferrites have a nanocrystalline structure with a crystallite size of about 30 and 40 nm for cases (1) and (2), respectively. There are five Raman and four IR active modes. In order to understand better the whole process of phase formation, the Mössbauer measurements were done.
2
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Characterization of Barium Titanate Ceramic Powders by Raman Spectroscopy

86%
Lazarević Z., Romčević N., Vijatović M., Paunović N., Romčević M., Stojanović B., Dohčević-Mitrović Z.
Acta Physica Polonica A
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2009
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vol. 115
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issue 4
808-810
EN
Barium titanate, BaTiO_3 ceramic powders were prepared by mechanochemical synthesis and by the Pechini method. A powder mixture of BaO and TiO_2 was treated in a planetary ball mill in an air atmosphere for up to 1 h, using zirconium oxide vial and zirconium oxide balls as the milling medium. After 60 min BaTiO_3 phase was formed. In both ways BaTiO_3 ceramics were sintered after 2 h on 1300°C without pre-calcinations step. The heating rate was 10°C min^{-1}. The formation of phase and crystal structure of BaTiO_3 was approved by X-ray diffraction analysis and the Raman spectroscopy. The morphology and microstructure of obtained powders were examined by scanning electron microscopy method. Sharp phase transition from ferroelectric to paraelectric state was observed. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials.
3
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Optical Properties of Plastically Deformed Copper

73%
Trajić J., Rudolf R., Anžel I., Romčević M., Lazarević N., Mirić M., Lazarević Z., Hadžić B., Romčević N.
Acta Physica Polonica A
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2010
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vol. 117
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issue 5
791-793
EN
Pure copper (99.99), prepared in the sample of square cross-section (10 × 10 mm^{2}) and length about 50 mm, was extremely plastically deformed with the repeated application of Equal Channel Angular Pressing (ECAP). ECAP was applied as an effective technique for producing bulk nano-scaled structures. Optical properties of the sample were investigated using Raman spectroscopy. Two types of lines: narrow (with width of ≈ 7 cm^{-1}) and wide ( ≈ 40 cm^{-1}) are registered. Existence of two types of lines indicates that in the specimen exists nano-sized crystal structures of both Cu and CuO related with three dimensional amorphous boundary spaces, which indicates that plastic deformation of the sample did not lead to total amorphisation of the specimen.
4
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Raman Spectroscopy of Multiphonon Emission Process in Ni-Doped PbTe

73%
Romčević N., Trajić J., Hadžić B., Romčević M., Stojanović D., Lazarević Z., Kuznetsova T., Khokhlov D., Rudolf R., Anžel I.
Acta Physica Polonica A
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2009
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vol. 116
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issue 1
91-92
EN
In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the sample used here was 1× 10^{19} at./cm^{3}. Well resolved peaks appear at about 126, 143, 181, 362 and 724 cm^{-1}. The modes at 126 and 143 cm^{-1}, which are also observed in other telluride compounds, originate from vibrations in TeO_2. We assume that the mode at about 181 cm^{-1} is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor Ni^{3+} state). Modes at about 362 cm^{-1} and 724 cm^{-1} are the second and fourth harmonic of a local phonon mode, registered here due to multiphonon emission.
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