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Characterization of La-Doped TiO_2 Nanopowders by Raman Spectroscopy

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Šćepanović M., Aškrabić S., Berec V., Golubović A., Dohčević-Mitrović Z., Kremenović A., Popović Z.
Acta Physica Polonica A
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2009
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vol. 115
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issue 4
771-774
EN
Titanium dioxide (TiO_2) nanopowders doped with 0.65, 1, 2, 3 and 4 wt.% of lanthanum ions (La^{3+}) were synthesized by sol-gel technology. Dependence of structural and morphological characteristics of nanopowders on La^{3+} content and synthesis conditions is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of TiO_2. Additional Raman modes of extremely low intensity can be related to the presence of certain amount of highly disordered brookite phase in nanopowders. Dependence of the intensity ratio of the Raman modes which originate from anatase and brookite on doping conditions is specially analyzed. In order to estimate the variation of nanocrystallite size with dopant content, shift and asymmetrical broadening of the most intensive E_g Raman mode of anatase are analyzed by phonon confinement model. The obtained results are compared with the results of X-ray diffraction spectroscopy. Special attention is dedicated to the changes in the Raman spectra of pure and La-doped TiO_2 nanopowders observed after high temperature treatment.
2
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Hydrothermal Synthesis of CeO_{2} and Ce_{0.9}Fe_{0.1}O_{2} Nanocrystals

100%
Radović M., Dohčević-Mitrović Z., Golubović A., Matović B., Šćepanović M., Popović Z.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
614-617
EN
Pure and 10 mol% Fe^{3+} doped CeO_2 nanocrystals were synthesized by hydrothermal method using two different basic solutions (NH_4OH and NaOH). All the samples were calcinated at 140°C and 200°C. The characterization of crystalline structure, vibrational and optical properties was performed using X-ray diffraction, Raman spectroscopy and spectroscopic ellipsometry. The obtained results showed that the Fe-doped samples are solid solutions with different size of nanocrystals, very dependent on the synthesis temperature and type of basic solution. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas doping provokes a small decrease of optical absorption edge in comparison with pure ceria.
3
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Low-Frequency Raman Spectroscopy of Pure and La-Doped TiO_2 Nanopowders Synthesized by Sol-Gel Method

100%
Šćepanović M., Aškrabić S., Grujić-Brojčin M., Golubović A., Dohčević-Mitrović Z., Kremenović A., Popović Z.
Acta Physica Polonica A
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2009
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vol. 116
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issue 1
99-102
EN
Pure and La-doped titania (TiO_2) nanopowders are synthesized by sol-gel technology. The crystallite sizes determined by X-ray diffraction measurements range from 10 to 15 nm. Dependence of structural and morphological characteristics of nanopowders on synthesis conditions and La^{3+} content is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of TiO_2. Additional Raman modes of extremely low intensity can be related to the presence of a small amount of brookite amorphous phase in nanopowders, which is in accordance with the results of X-ray diffraction analysis. The particle size distribution in TiO_2 nanopowders was estimated from the low frequency Raman spectra, using the fact that the phonon modes in nanosized TiO_2 observed in the low frequency region (ω <40 cm^{-1}) can be well described by the elastic continuum model, assuming that nanoparticles are of perfect spherical shape and isotropic. The nanosized particle distribution obtained by this method is used for the calculation of the frequency and shape of the most intensive E_g Raman mode in anatase TiO_2 by the phonon confinement model. The calculated broadening of this mode, associated with the particle size distribution, coincides well with the characteristics of E_g mode observed in measured Raman spectra of TiO_2 nanopowders. This confirms the Raman spectroscopy method as a powerful tool for determination of particle size distribution in nanosized materials.
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