Kahlenberg, V.

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  • Kahlenberg, V. (4)
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Author's Bibliography

Oxygen vacancy-induced microstructural changes of annealed CeO2-x nanocrystals

Askrabic, S.; Dohcevic-Mitrovic, Z.; Kremenović, Aleksandar S.; Lazarević, Nataša; Kahlenberg, V.; Popović, Zoran V.

(2012)

TY  - JOUR
AU  - Askrabic, S.
AU  - Dohcevic-Mitrovic, Z.
AU  - Kremenović, Aleksandar S.
AU  - Lazarević, Nataša
AU  - Kahlenberg, V.
AU  - Popović, Zoran V.
PY  - 2012
UR  - http://vinar.vin.bg.ac.rs/handle/123456789/4661
AB  - Nanocrystalline ceria (CeO2) is known for its ionic conductivity and oxygen storage properties, which depend on the presence of oxygen ion vacancies. The vacancies cause several important changes in CeO2 involving microstrain, electronic structure, magnetic properties, etc. In this article, we focus our attention to the microstructural changes of nanocrystalline CeO2-x annealed at different temperatures in the range 200500 degrees C. Structural and vibrational properties were investigated by X-ray diffraction and Raman spectroscopy. It was observed that the content of oxygen vacancies changed significantly with increasing annealing temperature, which plays an important role in the observed microstructural changes of the annealed samples. We demonstrate that the observed microstrain changes, because of variable defect content, dominate over the crystallite size effect. This finding is opposite to the conclusions made by several other authors. A new mode, classified as a probable surface mode, was observed in the Raman spectra at similar to 480 cm(1), the appearance of which can be explained by the large defective structure and disorder in the ceria lattice. Copyright (c) 2011 John Wiley and Sons, Ltd.
T2  - Journal of Raman Spectroscopy
T1  - Oxygen vacancy-induced microstructural changes of annealed CeO2-x nanocrystals
VL  - 43
IS  - 1
SP  - 76
EP  - 81
DO  - 10.1002/jrs.2987
ER  - 
@article{
author = "Askrabic, S. and Dohcevic-Mitrovic, Z. and Kremenović, Aleksandar S. and Lazarević, Nataša and Kahlenberg, V. and Popović, Zoran V.",
year = "2012",
abstract = "Nanocrystalline ceria (CeO2) is known for its ionic conductivity and oxygen storage properties, which depend on the presence of oxygen ion vacancies. The vacancies cause several important changes in CeO2 involving microstrain, electronic structure, magnetic properties, etc. In this article, we focus our attention to the microstructural changes of nanocrystalline CeO2-x annealed at different temperatures in the range 200500 degrees C. Structural and vibrational properties were investigated by X-ray diffraction and Raman spectroscopy. It was observed that the content of oxygen vacancies changed significantly with increasing annealing temperature, which plays an important role in the observed microstructural changes of the annealed samples. We demonstrate that the observed microstrain changes, because of variable defect content, dominate over the crystallite size effect. This finding is opposite to the conclusions made by several other authors. A new mode, classified as a probable surface mode, was observed in the Raman spectra at similar to 480 cm(1), the appearance of which can be explained by the large defective structure and disorder in the ceria lattice. Copyright (c) 2011 John Wiley and Sons, Ltd.",
journal = "Journal of Raman Spectroscopy",
title = "Oxygen vacancy-induced microstructural changes of annealed CeO2-x nanocrystals",
volume = "43",
number = "1",
pages = "76-81",
doi = "10.1002/jrs.2987"
}
Askrabic, S., Dohcevic-Mitrovic, Z., Kremenović, A. S., Lazarević, N., Kahlenberg, V.,& Popović, Z. V.. (2012). Oxygen vacancy-induced microstructural changes of annealed CeO2-x nanocrystals. in Journal of Raman Spectroscopy, 43(1), 76-81.
https://doi.org/10.1002/jrs.2987
Askrabic S, Dohcevic-Mitrovic Z, Kremenović AS, Lazarević N, Kahlenberg V, Popović ZV. Oxygen vacancy-induced microstructural changes of annealed CeO2-x nanocrystals. in Journal of Raman Spectroscopy. 2012;43(1):76-81.
doi:10.1002/jrs.2987 .
Askrabic, S., Dohcevic-Mitrovic, Z., Kremenović, Aleksandar S., Lazarević, Nataša, Kahlenberg, V., Popović, Zoran V., "Oxygen vacancy-induced microstructural changes of annealed CeO2-x nanocrystals" in Journal of Raman Spectroscopy, 43, no. 1 (2012):76-81,
https://doi.org/10.1002/jrs.2987 . .
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Influence of size/crystallinity effects on the cation ordering and magnetism of alpha-lithium ferrite nanoparticles

Jović, Nataša G.; Prekajski, Marija D.; Kremenović, Aleksandar S.; Jančar, Boštjan; Kahlenberg, V.; Antić, Bratislav

(2012)

TY  - JOUR
AU  - Jović, Nataša G.
AU  - Prekajski, Marija D.
AU  - Kremenović, Aleksandar S.
AU  - Jančar, Boštjan
AU  - Kahlenberg, V.
AU  - Antić, Bratislav
PY  - 2012
UR  - http://vinar.vin.bg.ac.rs/handle/123456789/4721
AB  - alpha-lithium ferrite (Li0.5Fe2.5O4) nanoparticles have been prepared using two synthesis routes: citrate gel decomposition as well as the Pechini method. Analysis of HRTEM images of the particles showed that they have a core/shell structure, an average size of similar to 10 nm and stacking faults parallel to the (110) planes. In both samples, the distribution of the Li and Fe cations was found to be partially ordered on the octahedral sites (Wyckoff positions 4b and 12d of space group P4(3)32). According to literature data, Li0.5Fe2.5O4 should adopt a disordered spinel structure (so called beta-phase, space group Fd (3) over barm) for crystallites of 10 nm or less in size. In this study it is shown that (a) the symmetry of the Li0.5Fe2.5O4 nanoparticles depends on the degree of their crystallinity and (b) the ordered crystal structures can be formed even for crystallites of 5-6 nm in size. By fitting the room temperature Mossbauer spectra it was obtained that the hyperfine field values are lower in the sample synthesized by the Pechini method. The Pechini process probably resulted in larger distortions of the cation environments than the citrate gel decomposition method. The saturation magnetization in turn was higher for the material obtained by the gel decomposition approach. (C) 2012 American Institute of Physics. [doi:10.1063/1.3684554]
T2  - Journal of Applied Physics
T1  - Influence of size/crystallinity effects on the cation ordering and magnetism of alpha-lithium ferrite nanoparticles
VL  - 111
IS  - 3
DO  - 10.1063/1.3684554
ER  - 
@article{
author = "Jović, Nataša G. and Prekajski, Marija D. and Kremenović, Aleksandar S. and Jančar, Boštjan and Kahlenberg, V. and Antić, Bratislav",
year = "2012",
abstract = "alpha-lithium ferrite (Li0.5Fe2.5O4) nanoparticles have been prepared using two synthesis routes: citrate gel decomposition as well as the Pechini method. Analysis of HRTEM images of the particles showed that they have a core/shell structure, an average size of similar to 10 nm and stacking faults parallel to the (110) planes. In both samples, the distribution of the Li and Fe cations was found to be partially ordered on the octahedral sites (Wyckoff positions 4b and 12d of space group P4(3)32). According to literature data, Li0.5Fe2.5O4 should adopt a disordered spinel structure (so called beta-phase, space group Fd (3) over barm) for crystallites of 10 nm or less in size. In this study it is shown that (a) the symmetry of the Li0.5Fe2.5O4 nanoparticles depends on the degree of their crystallinity and (b) the ordered crystal structures can be formed even for crystallites of 5-6 nm in size. By fitting the room temperature Mossbauer spectra it was obtained that the hyperfine field values are lower in the sample synthesized by the Pechini method. The Pechini process probably resulted in larger distortions of the cation environments than the citrate gel decomposition method. The saturation magnetization in turn was higher for the material obtained by the gel decomposition approach. (C) 2012 American Institute of Physics. [doi:10.1063/1.3684554]",
journal = "Journal of Applied Physics",
title = "Influence of size/crystallinity effects on the cation ordering and magnetism of alpha-lithium ferrite nanoparticles",
volume = "111",
number = "3",
doi = "10.1063/1.3684554"
}
Jović, N. G., Prekajski, M. D., Kremenović, A. S., Jančar, B., Kahlenberg, V.,& Antić, B.. (2012). Influence of size/crystallinity effects on the cation ordering and magnetism of alpha-lithium ferrite nanoparticles. in Journal of Applied Physics, 111(3).
https://doi.org/10.1063/1.3684554
Jović NG, Prekajski MD, Kremenović AS, Jančar B, Kahlenberg V, Antić B. Influence of size/crystallinity effects on the cation ordering and magnetism of alpha-lithium ferrite nanoparticles. in Journal of Applied Physics. 2012;111(3).
doi:10.1063/1.3684554 .
Jović, Nataša G., Prekajski, Marija D., Kremenović, Aleksandar S., Jančar, Boštjan, Kahlenberg, V., Antić, Bratislav, "Influence of size/crystallinity effects on the cation ordering and magnetism of alpha-lithium ferrite nanoparticles" in Journal of Applied Physics, 111, no. 3 (2012),
https://doi.org/10.1063/1.3684554 . .
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HEBM synthesis of nanocrystalline LiZn0.5Ti1.5O4 spinel and thermally induced order-disorder phase transition(P4(3)32 - GT Fd(3)over-barm)

Jović, Nataša G.; Vučinić-Vasić, Milica; Kremenović, Aleksandar S.; Antić, Bratislav; Jovalekic, Cedomir; Vulic, P.; Kahlenberg, V.; Kaindl, R.

(2009)

TY  - JOUR
AU  - Jović, Nataša G.
AU  - Vučinić-Vasić, Milica
AU  - Kremenović, Aleksandar S.
AU  - Antić, Bratislav
AU  - Jovalekic, Cedomir
AU  - Vulic, P.
AU  - Kahlenberg, V.
AU  - Kaindl, R.
PY  - 2009
UR  - http://vinar.vin.bg.ac.rs/handle/123456789/3753
AB  - Nanocrystalline LiZn0.5Ti1.5O4 disordered spinel (S.G. Fd (3) over barm) was synthesized by high energy ball milling (HEBM). TEM analysis of the sample has shown that the particle size distribution is broad ranging from 10 to 60 nm. By X-ray line broadening analysis, the average apparent size of the crystallites is found to be 19(1) nm, while the average apparent strain is 26(4) x 10(-4). The cation distribution was found to be metastable, with Zn in octahedral 16d and Ti in tetrahedral 8a position, against their known site preference. After annealing the sample at 650 degrees C for 3 h and slow cooling down to room temperature, superstructure reflections (110), (210), (211) have been observed, indicating a cation ordering in the octahedral sublattice and a combined symmetry reduction (S.G. P4(3)32). The reverse symmetry change P4(3)32 - GT Fd (3) over barm caused by increasing the temperature was studied by in situ XRPD, DSC/DTA, Landaus theory of phase transitions and Raman spectroscopy. An analysis of the topology of the order parameter vector space indicates a biquadratic or linear-quadratic coupling between the order parameters Q(1) and Q(2). In LiZn0.5Ti1.5O4 dilatation expansion of crystal lattice as well as spontaneous strain values are rather small (order of 10(-4)), comparing to e.g. Li1.33xCo2-2xTi1+0.67xO4. (C) 2009 Elsevier B.V. All rights reserved.
T2  - Materials Chemistry and Physics
T1  - HEBM synthesis of nanocrystalline LiZn0.5Ti1.5O4 spinel and thermally induced order-disorder phase transition(P4(3)32 - GT Fd(3)over-barm)
VL  - 116
IS  - 2-3
SP  - 542
EP  - 549
DO  - 10.1016/j.matchemphys.2009.04.033
ER  - 
@article{
author = "Jović, Nataša G. and Vučinić-Vasić, Milica and Kremenović, Aleksandar S. and Antić, Bratislav and Jovalekic, Cedomir and Vulic, P. and Kahlenberg, V. and Kaindl, R.",
year = "2009",
abstract = "Nanocrystalline LiZn0.5Ti1.5O4 disordered spinel (S.G. Fd (3) over barm) was synthesized by high energy ball milling (HEBM). TEM analysis of the sample has shown that the particle size distribution is broad ranging from 10 to 60 nm. By X-ray line broadening analysis, the average apparent size of the crystallites is found to be 19(1) nm, while the average apparent strain is 26(4) x 10(-4). The cation distribution was found to be metastable, with Zn in octahedral 16d and Ti in tetrahedral 8a position, against their known site preference. After annealing the sample at 650 degrees C for 3 h and slow cooling down to room temperature, superstructure reflections (110), (210), (211) have been observed, indicating a cation ordering in the octahedral sublattice and a combined symmetry reduction (S.G. P4(3)32). The reverse symmetry change P4(3)32 - GT Fd (3) over barm caused by increasing the temperature was studied by in situ XRPD, DSC/DTA, Landaus theory of phase transitions and Raman spectroscopy. An analysis of the topology of the order parameter vector space indicates a biquadratic or linear-quadratic coupling between the order parameters Q(1) and Q(2). In LiZn0.5Ti1.5O4 dilatation expansion of crystal lattice as well as spontaneous strain values are rather small (order of 10(-4)), comparing to e.g. Li1.33xCo2-2xTi1+0.67xO4. (C) 2009 Elsevier B.V. All rights reserved.",
journal = "Materials Chemistry and Physics",
title = "HEBM synthesis of nanocrystalline LiZn0.5Ti1.5O4 spinel and thermally induced order-disorder phase transition(P4(3)32 - GT Fd(3)over-barm)",
volume = "116",
number = "2-3",
pages = "542-549",
doi = "10.1016/j.matchemphys.2009.04.033"
}
Jović, N. G., Vučinić-Vasić, M., Kremenović, A. S., Antić, B., Jovalekic, C., Vulic, P., Kahlenberg, V.,& Kaindl, R.. (2009). HEBM synthesis of nanocrystalline LiZn0.5Ti1.5O4 spinel and thermally induced order-disorder phase transition(P4(3)32 - GT Fd(3)over-barm). in Materials Chemistry and Physics, 116(2-3), 542-549.
https://doi.org/10.1016/j.matchemphys.2009.04.033
Jović NG, Vučinić-Vasić M, Kremenović AS, Antić B, Jovalekic C, Vulic P, Kahlenberg V, Kaindl R. HEBM synthesis of nanocrystalline LiZn0.5Ti1.5O4 spinel and thermally induced order-disorder phase transition(P4(3)32 - GT Fd(3)over-barm). in Materials Chemistry and Physics. 2009;116(2-3):542-549.
doi:10.1016/j.matchemphys.2009.04.033 .
Jović, Nataša G., Vučinić-Vasić, Milica, Kremenović, Aleksandar S., Antić, Bratislav, Jovalekic, Cedomir, Vulic, P., Kahlenberg, V., Kaindl, R., "HEBM synthesis of nanocrystalline LiZn0.5Ti1.5O4 spinel and thermally induced order-disorder phase transition(P4(3)32 - GT Fd(3)over-barm)" in Materials Chemistry and Physics, 116, no. 2-3 (2009):542-549,
https://doi.org/10.1016/j.matchemphys.2009.04.033 . .
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A Y2O3 : Yb nanoscale magnet obtained by HEBM: C-3i/C-2 site occupancies, size/strain analysis and crystal field levels of Yb3+ ions

Kremenović, Aleksandar S.; Blanuša, Jovan; Antić, Bratislav; Colomban, Ph; Kahlenberg, V.; Jovalekic, Cedomir; Dukić, Jelena

(2007)

TY  - JOUR
AU  - Kremenović, Aleksandar S.
AU  - Blanuša, Jovan
AU  - Antić, Bratislav
AU  - Colomban, Ph
AU  - Kahlenberg, V.
AU  - Jovalekic, Cedomir
AU  - Dukić, Jelena
PY  - 2007
UR  - http://vinar.vin.bg.ac.rs/handle/123456789/3176
AB  - A Y2O3: Yb nanoscale magnet that belongs to the cubic C-type or bixbyite structure family was synthesized by high energy ball milling ( HEBM). An as-prepared sample ( S1) was annealed at 650 degrees C ( S2) and 950 degrees C ( S3). Cation populations were determined by the refinement of site occupancies. It was found that in S1 and S2 Yb3+ ions occupy exclusively the 8b ( or C-3i) position, whereas in S3 a small amount of Yb3+ is also located on Wyckoff-site 24d ( or C-2). X-ray powder diffraction line broadening analysis was done by using the Rietveld method using regular TCH-pV functions ( isotropic effects) and symmetrized cubic harmonics ( anisotropic effects) for the refinement. The line broadening anisotropy decreases due to strain effects from S1 to S3, while the crystallite size anisotropy increases from S1 to S3. Transmission electron microscopy ( TEM) and Raman spectroscopy were used to define the homogeneity, microstructure and to locally probe the structure of the samples S1-S3. Magnetic susceptibility results in the 2-300 K temperature regions were analysed by applying the first-order perturbation theory. The mean energy gap between ground and excited crystal field levels ( E-i), and their effective magnetic numbers M-ieff, were determined. The analysis of the paramagnetic temperature shows the absence of clusterization of the magnetic ions.
T2  - Nanotechnology
T1  - A Y2O3 : Yb nanoscale magnet obtained by HEBM: C-3i/C-2 site occupancies, size/strain analysis and crystal field levels of Yb3+ ions
VL  - 18
IS  - 14
DO  - 10.1088/0957-4484/18/14/145616
ER  - 
@article{
author = "Kremenović, Aleksandar S. and Blanuša, Jovan and Antić, Bratislav and Colomban, Ph and Kahlenberg, V. and Jovalekic, Cedomir and Dukić, Jelena",
year = "2007",
abstract = "A Y2O3: Yb nanoscale magnet that belongs to the cubic C-type or bixbyite structure family was synthesized by high energy ball milling ( HEBM). An as-prepared sample ( S1) was annealed at 650 degrees C ( S2) and 950 degrees C ( S3). Cation populations were determined by the refinement of site occupancies. It was found that in S1 and S2 Yb3+ ions occupy exclusively the 8b ( or C-3i) position, whereas in S3 a small amount of Yb3+ is also located on Wyckoff-site 24d ( or C-2). X-ray powder diffraction line broadening analysis was done by using the Rietveld method using regular TCH-pV functions ( isotropic effects) and symmetrized cubic harmonics ( anisotropic effects) for the refinement. The line broadening anisotropy decreases due to strain effects from S1 to S3, while the crystallite size anisotropy increases from S1 to S3. Transmission electron microscopy ( TEM) and Raman spectroscopy were used to define the homogeneity, microstructure and to locally probe the structure of the samples S1-S3. Magnetic susceptibility results in the 2-300 K temperature regions were analysed by applying the first-order perturbation theory. The mean energy gap between ground and excited crystal field levels ( E-i), and their effective magnetic numbers M-ieff, were determined. The analysis of the paramagnetic temperature shows the absence of clusterization of the magnetic ions.",
journal = "Nanotechnology",
title = "A Y2O3 : Yb nanoscale magnet obtained by HEBM: C-3i/C-2 site occupancies, size/strain analysis and crystal field levels of Yb3+ ions",
volume = "18",
number = "14",
doi = "10.1088/0957-4484/18/14/145616"
}
Kremenović, A. S., Blanuša, J., Antić, B., Colomban, P., Kahlenberg, V., Jovalekic, C.,& Dukić, J.. (2007). A Y2O3 : Yb nanoscale magnet obtained by HEBM: C-3i/C-2 site occupancies, size/strain analysis and crystal field levels of Yb3+ ions. in Nanotechnology, 18(14).
https://doi.org/10.1088/0957-4484/18/14/145616
Kremenović AS, Blanuša J, Antić B, Colomban P, Kahlenberg V, Jovalekic C, Dukić J. A Y2O3 : Yb nanoscale magnet obtained by HEBM: C-3i/C-2 site occupancies, size/strain analysis and crystal field levels of Yb3+ ions. in Nanotechnology. 2007;18(14).
doi:10.1088/0957-4484/18/14/145616 .
Kremenović, Aleksandar S., Blanuša, Jovan, Antić, Bratislav, Colomban, Ph, Kahlenberg, V., Jovalekic, Cedomir, Dukić, Jelena, "A Y2O3 : Yb nanoscale magnet obtained by HEBM: C-3i/C-2 site occupancies, size/strain analysis and crystal field levels of Yb3+ ions" in Nanotechnology, 18, no. 14 (2007),
https://doi.org/10.1088/0957-4484/18/14/145616 . .
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