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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.
2
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Optical Characterization of Graphene and Highly Oriented Pyrolytic Graphite

100%
Kostić R., Mirić M., Radić T., Radović M., Gajić R., Popović Z.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
718-721
EN
We present a symmetry analysis of allowed infrared and Raman modes in graphene and highly oriented pyrolytic graphite. Surface structure for highly oriented pyrolytic graphite is examined using atomic force microscopy. As experimental tools, we used infrared spectroscopic ellipsometry in order to investigate the pseudodielectric function of highly oriented pyrolytic graphite in the mid-infrared range (500-7000 cm^{-1}) and Raman spectroscopy to investigate the influence of layers number decrease. As a result, we propose a method for an experimental verification of graphene.
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Effect of Fe^{2+} (Fe^{3+}) Doping on Structural Properties οf CeO_2 Nanocrystals

100%
Radović M., Dohčević-Mitrović Z., Paunović N., Šćepanović M., Matović B., Popović Z.
Acta Physica Polonica A
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2009
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vol. 116
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issue 1
84-87
EN
We have measured the Raman scattering and magnetization of pure and Fe^{2+}(Fe^{3+}) doped CeO_2 nanopowders at room temperature. The Raman scattering spectra revealed the existence of CeO_2 fluorite cubic structure for all investigated samples. The Raman active mode at about 600 cm^{-1}, seen in all samples, can be ascribed to the CeO_2 intrinsic oxygen vacancies. Additional Raman modes at 720 cm^{-1}, 1320 cm^{-1} and 1600 cm^{-1}, which appear in the spectra of doped samples, can be assigned to maghemite (γ-Fe_2O_3) cation deficient structure, to 2ω_{LO} IR-allowed overtone and two magnon structure, respectively. This implies that our powders are composed of mixed valence states and have defective structure. Presence of oxygen defect states and magnetic ions can be responsible for the observed ferromagnetism at room temperature in both pure and Fe doped samples.
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