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3 Acta Physica Polonica A

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Characterization of Barium Titanate Ceramic Powders by Raman Spectroscopy

100%

Lazarević Z. , Romčević N. , Vijatović M. , Paunović N. , Romčević M. , Stojanović B. , Dohčević-Mitrović Z.

Acta Physica Polonica A

2009

tom 115

nr 4

808-810

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.

Optical Properties of Plastically Deformed Copper

84%

Trajić J. , Rudolf R. , Anžel I. , Romčević M. , Lazarević N. , Mirić M. , Lazarević Z. , Hadžić B. , Romčević N.

Acta Physica Polonica A

2010

tom 117

nr 5

791-793

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.

Raman Spectroscopy of Multiphonon Emission Process in Ni-Doped PbTe

84%

Romčević N. , Trajić J. , Hadžić B. , Romčević M. , Stojanović D. , Lazarević Z. , Kuznetsova T. , Khokhlov D. , Rudolf R. , Anžel I.

Acta Physica Polonica A

2009

tom 116

nr 1

91-92

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.